In the human body, the work of all its organs is closely interconnected, and therefore the body functions as a whole. The coordination of the functions of the internal organs is provided by the nervous system. In addition, the nervous system communicates between the external environment and the regulatory body, responding to external stimuli with appropriate reactions.

The perception of changes occurring in the external and internal environment occurs through nerve endings - receptors.

Any irritation (mechanical, light, sound, chemical, electrical, temperature) perceived by the receptor is converted (transformed) into the process of excitation. Excitation is transmitted along sensitive - centripetal nerve fibers to the central nervous system, where an urgent process of processing nerve impulses takes place. From here, impulses are sent along the fibers of centrifugal neurons (motor) to the executive organs that implement the response - the corresponding adaptive act.

This is how a reflex is performed (from the Latin "reflexus" - reflection) - a natural reaction of the body to changes in the external or internal environment, carried out through the central nervous system in response to irritation of receptors.

Reflex reactions are diverse: this is the narrowing of the pupil in bright light, the release of saliva when food enters the oral cavity, etc.

The path along which nerve impulses (excitation) pass from receptors to the executive organ during the implementation of any reflex is called reflex arc.

The arcs of the reflexes close in the segmental apparatus of the spinal cord and brainstem, but they can also close higher, for example, in the subcortical ganglia or in the cortex.

Based on the foregoing, there are:

central nervous system (brain and spinal cord) and
peripheral nervous system, represented by nerves extending from the brain and spinal cord and other elements that lie outside the spinal cord and brain.

The peripheral nervous system is divided into somatic (animal) and autonomic (or autonomic).

The somatic nervous system mainly carries out the connection of the organism with the external environment: the perception of stimuli, the regulation of movements of the striated muscles of the skeleton, etc.
vegetative - regulates metabolism and the functioning of internal organs: heartbeat, peristaltic contractions of the intestines, secretion of various glands, etc.

The autonomic nervous system, in turn, based on the segmental principle of structure, is divided into two levels:

segmental - includes sympathetic, anatomically associated with the spinal cord, and parasympathetic, formed by accumulations of nerve cells in the midbrain and medulla oblongata, nervous systems
suprasegmental level - includes the reticular formation of the brain stem, hypothalamus, thalamus, amygdala and hippocampus - limbic-reticular complex

The somatic and autonomic nervous systems function in close interaction, however, the autonomic nervous system has some independence (autonomy), controlling many involuntary functions.

CENTRAL NERVOUS SYSTEM

Represented by the brain and spinal cord. The brain is made up of gray and white matter.

Gray matter is a collection of neurons and their short processes. In the spinal cord, it is located in the center, surrounding the spinal canal. In the brain, on the contrary, gray matter is located on its surface, forming a cortex (cloak) and separate clusters, called nuclei, concentrated in white matter.

The white matter is under the gray and is composed of sheathed nerve fibers. Nerve fibers, connecting, compose nerve bundles, and several such bundles form individual nerves.

The nerves through which excitation is transmitted from the central nervous system to the organs are called centrifugal, and the nerves that conduct excitation from the periphery to the central nervous system are called centripetal.

The brain and spinal cord are surrounded by three membranes: hard, arachnoid and vascular.

Solid - external, connective tissue, lines the internal cavity of the skull and spinal canal.
The arachnoid is located under the solid - it is a thin shell with a small number of nerves and blood vessels.
The choroid is fused with the brain, enters the furrows and contains many blood vessels.

Cavities filled with cerebral fluid form between the vascular and arachnoid membranes.

Spinal cord located in the spinal canal and has the appearance of a white cord, stretching from the occipital foramen to the lower back. Longitudinal grooves are located along the anterior and posterior surfaces of the spinal cord, in the center there is a spinal canal, around which gray matter is concentrated - an accumulation of a huge number of nerve cells that form the contour of a butterfly. On the outer surface of the cord of the spinal cord is white matter - an accumulation of bundles of long processes of nerve cells.

The gray matter is divided into anterior, posterior and lateral horns. In the anterior horns lie motor neurons, in the posterior - intercalary, which carry out the connection between sensory and motor neurons. Sensory neurons lie outside the cord, in the spinal nodes along the sensory nerves.

Long processes depart from the motor neurons of the anterior horns - the anterior roots, which form the motor nerve fibers. The axons of sensitive neurons approach the posterior horns, forming the posterior roots, which enter the spinal cord and transmit excitation from the periphery to the spinal cord. Here, excitation switches to the intercalary neuron, and from it to short processes of the motor neuron, from which it is then transmitted along the axon to the working organ.

In the intervertebral foramina, the motor and sensory roots join to form mixed nerves, which then split into anterior and posterior branches. Each of them consists of sensory and motor nerve fibers. Thus, at the level of each vertebra, only 31 pairs of spinal nerves of a mixed type depart from the spinal cord in both directions.

The white matter of the spinal cord forms pathways that stretch along the spinal cord, connecting both its individual segments to each other, and the spinal cord to the brain. Some pathways are called ascending or sensitive, transmitting excitation to the brain, others are descending or motor, which conduct impulses from the brain to certain segments of the spinal cord.

The function of the spinal cord. The spinal cord has two functions:

reflex [show] .
Each reflex is carried out by a strictly defined part of the central nervous system - the nerve center. The nerve center is a collection of nerve cells located in one of the parts of the brain and regulating the activity of any organ or system. For example, the center of the knee-jerk reflex is located in the lumbar spinal cord, the center of urination is in the sacral, and the center of pupil dilation is in the upper thoracic segment of the spinal cord. The vital motor center of the diaphragm is localized in the III-IV cervical segments. Other centers - respiratory, vasomotor - are located in the medulla oblongata.
The nerve center consists of many intercalary neurons. It processes the information that comes from the corresponding receptors, and generates impulses that are transmitted to the executive organs - the heart, blood vessels, skeletal muscles, glands, etc. As a result, their functional state changes. To regulate the reflex, its accuracy, the participation of the higher parts of the central nervous system, including the cerebral cortex, is also necessary.
The nerve centers of the spinal cord are directly connected with the receptors and executive organs of the body. The motor neurons of the spinal cord provide contraction of the muscles of the trunk and limbs, as well as the respiratory muscles - the diaphragm and intercostals. In addition to the motor centers of skeletal muscles, there are a number of autonomic centers in the spinal cord.
conductive [show] .

The bundles of nerve fibers that form the white matter connect the various parts of the spinal cord to each other and the brain to the spinal cord. There are ascending pathways, carrying impulses to the brain, and descending, carrying impulses from the brain to the spinal cord. According to the first, excitation that occurs in the receptors of the skin, muscles, and internal organs is carried along the spinal nerves to the posterior roots of the spinal cord, is perceived by the sensitive neurons of the spinal ganglions, and from here it is sent either to the posterior horns of the spinal cord, or as part of the white matter reaches the trunk, and then the cerebral cortex.

Descending pathways conduct excitation from the brain to the motor neurons of the spinal cord. From here, the excitation is transmitted along the spinal nerves to the executive organs. The activity of the spinal cord is under the control of the brain, which regulates spinal reflexes.

Brain is located in cerebral region skulls. Its average weight is 1300 - 1400 g. After the birth of a person, brain growth continues up to 20 years. It consists of five sections: the anterior (large hemispheres), intermediate, middle, hindbrain and medulla oblongata. Inside the brain there are four interconnected cavities - cerebral ventricles. They are filled with cerebrospinal fluid. I and II ventricles are located in the cerebral hemispheres, III - in the diencephalon, and IV - in the medulla oblongata.

The hemispheres (the newest part in evolutionary terms) reach high development in humans, accounting for 80% of the mass of the brain. The phylogenetically older part is the brain stem. The trunk includes the medulla oblongata, the medullary (varoli) bridge, the midbrain and the diencephalon.

Numerous nuclei of gray matter lie in the white matter of the trunk. The nuclei of 12 pairs of cranial nerves also lie in the brainstem. The brain stem is covered by the cerebral hemispheres.

Medulla- a continuation of the dorsal and repeats its structure: furrows also lie on the anterior and posterior surfaces. It consists of white matter (conducting bundles), where clusters of gray matter are scattered - the nuclei from which cranial nerves originate - from IX to XII pairs, including glossopharyngeal (IX pair), vagus (X pair), innervating organs respiration, circulation, digestion and other systems, sublingual (XII pair). At the top, the medulla oblongata continues into a thickening - the pons varolii, and from the sides the lower legs of the cerebellum depart from it. From above and from the sides, almost the entire medulla oblongata is covered by the cerebral hemispheres and the cerebellum.

In the gray matter of the medulla oblongata lie vital centers that regulate cardiac activity, breathing, swallowing, carrying out protective reflexes (sneezing, coughing, vomiting, tearing), secretion of saliva, gastric and pancreatic juice, etc. Damage to the medulla oblongata can be the cause of death due to the cessation heart activity and respiration.

Hind brain includes the pons and cerebellum. The pons of Varolii is limited from below by the medulla oblongata, from above it passes into the legs of the brain, its lateral sections form the middle legs of the cerebellum. In the substance of the pons, there are nuclei from the V to VIII pair of cranial nerves (trigeminal, abducent, facial, auditory).

The cerebellum is located posterior to the pons and medulla oblongata. Its surface consists of gray matter (bark). Under the cerebellar cortex is white matter, in which there are accumulations of gray matter - the nucleus. The entire cerebellum is represented by two hemispheres, the middle part is a worm and three pairs of legs formed by nerve fibers, through which it is connected with other parts of the brain. The main function of the cerebellum is the unconditional reflex coordination of movements, which determines their clarity, smoothness and maintaining body balance, as well as maintaining muscle tone. Through the spinal cord along the pathways, impulses from the cerebellum arrive at the muscles. The activity of the cerebellum is controlled by the cerebral cortex.

midbrain located in front of the pons, it is represented by the quadrigemina and the legs of the brain. In the center of it is a narrow canal (aqueduct of the brain), which connects the III and IV ventricles. The cerebral aqueduct is surrounded by gray matter, which contains the nuclei of the III and IV pairs of cranial nerves. In the legs of the brain, pathways continue from the medulla oblongata and the pons to the cerebral hemispheres. The midbrain plays an important role in the regulation of tone and in the implementation of reflexes, due to which standing and walking are possible. The sensitive nuclei of the midbrain are located in the tubercles of the quadrigemina: the nuclei associated with the organs of vision are enclosed in the upper ones, and the nuclei associated with the organs of hearing are in the lower ones. With their participation, orienting reflexes to light and sound are carried out.

diencephalon occupies the highest position in the trunk and lies anterior to the legs of the brain. It consists of two visual hillocks, supratuberous, hypothalamic region and geniculate bodies. On the periphery of the diencephalon is white matter, and in its thickness - the nuclei of gray matter. Visual hillocks are the main subcortical centers of sensitivity: impulses from all receptors of the body arrive here along ascending paths, and from here to the cerebral cortex. In the hypothalamic part (hypothalamus) there are centers, the totality of which is the highest subcortical center of the autonomic nervous system, which regulates the metabolism in the body, heat transfer, and the constancy of the internal environment. Parasympathetic centers are located in the anterior hypothalamus, and sympathetic centers in the posterior. The subcortical visual and auditory centers are concentrated in the nuclei of the geniculate bodies.

The 2nd pair of cranial nerves - optic nerves - goes to the geniculate bodies. The brain stem is connected to the environment and to the organs of the body by cranial nerves. By their nature, they can be sensitive (I, II, VIII pairs), motor (III, IV, VI, XI, XII pairs) and mixed (V, VII, IX, X pairs).

forebrain consists of strongly developed hemispheres and the middle part connecting them. The right and left hemispheres are separated from each other by a deep fissure, at the bottom of which lies the corpus callosum. The corpus callosum connects both hemispheres through long processes of neurons that form pathways.

The cavities of the hemispheres are represented by the lateral ventricles (I and II). The surface of the hemispheres is formed by gray matter or the cerebral cortex, represented by neurons and their processes, under the cortex lies white matter - pathways. Pathways connect individual centers within the same hemisphere, or the right and left halves of the brain and spinal cord, or different floors of the central nervous system. In the white matter there are also clusters of nerve cells that form the subcortical nuclei of the gray matter. Part of the cerebral hemispheres is the olfactory brain with a pair of olfactory nerves extending from it (I pair).

The total surface of the cerebral cortex is 2000-2500 cm 2, its thickness is 1.5-4 mm. Despite its small thickness, the cerebral cortex has a very complex structure.

The cortex includes more than 14 billion nerve cells, arranged in six layers that differ in shape, size of neurons and connections. The microscopic structure of the cortex was first studied by V. A. Betz. He discovered pyramidal neurons, which were later given his name (Betz cells).

In a three-month-old embryo, the surface of the hemispheres is smooth, but the cortex grows faster than the brain box, so the cortex forms folds - convolutions limited by furrows; they contain about 70% of the surface of the cortex. Furrows divide the surface of the hemispheres into lobes.

There are four lobes in each hemisphere:

frontal
parietal
temporal
occipital.

The deepest furrows are the central one, which runs across both hemispheres, and the temporal one, which separates the temporal lobe of the brain from the rest; the parieto-occipital sulcus separates the parietal lobe from the occipital lobe.

Anterior to the central sulcus (Roland sulcus) in the frontal lobe is the anterior central gyrus, behind it is the posterior central gyrus. The lower surface of the hemispheres and the brain stem is called the base of the brain.

Based on experiments with partial removal of different parts of the cortex in animals and observations on people with affected cortex, it was possible to establish the functions of different parts of the cortex. So, in the cortex of the occipital lobe of the hemispheres is the visual center, in the upper part of the temporal lobe - the auditory. The musculocutaneous zone, which perceives irritations from the skin of all parts of the body and controls the voluntary movements of the skeletal muscles, occupies a portion of the cortex on both sides of the central sulcus.

Each part of the body corresponds to its own section of the cortex, and the representation of the palms and fingers, lips and tongue, as the most mobile and sensitive parts of the body, occupies in a person almost the same area of the cortex as the representation of all other parts of the body combined.

In the cortex there are centers of all sensitive (receptor) systems, representations of all organs and parts of the body. In this regard, centripetal nerve impulses from all internal organs or parts of the body are suitable for the corresponding sensitive areas of the cerebral cortex, where analysis is carried out and a specific sensation is formed - visual, olfactory, etc., and it can control their work.

A functional system consisting of a receptor, a sensitive pathway and a cortical zone where this type of sensitivity is projected, I. P. Pavlov called the analyzer.

The analysis and synthesis of the received information is carried out in a strictly defined area - the zone of the cerebral cortex. The most important areas of the cortex are motor, sensory, visual, auditory, olfactory. The motor zone is located in the anterior central gyrus in front of the central sulcus of the frontal lobe, the zone of skin-muscular sensitivity is located behind the central sulcus, in the posterior central gyrus of the parietal lobe. The visual zone is concentrated in the occipital lobe, the auditory zone is in the superior temporal gyrus of the temporal lobe, and the olfactory and gustatory zones are in the anterior temporal lobe.

In the cerebral cortex, many nervous processes are carried out. Their purpose is twofold: the interaction of the body with the external environment (behavioral reactions) and the unification of body functions, the nervous regulation of all organs. The activity of the cerebral cortex of humans and higher animals was defined by I.P. Pavlov as the highest nervous activity, which is a conditioned reflex function of the cerebral cortex.

Nervous system	Central nervous system
	brain			spinal cord
	large hemispheres	cerebellum	trunk	spinal cord
Composition and structure	Lobes: frontal, parietal, occipital, two temporal. The cortex is formed by gray matter - the bodies of nerve cells. The thickness of the bark is 1.5-3 mm. The area of the cortex is 2-2.5 thousand cm 2, it consists of 14 billion bodies of neurons. White matter is made up of nerve fibers	The gray matter forms the cortex and nuclei within the cerebellum. Consists of two hemispheres connected by a bridge	Educated: diencephalon midbrain bridge medulla oblongata It consists of white matter, in the thickness are the nuclei of gray matter. The trunk passes into the spinal cord	Cylindrical cord 42-45 cm long and about 1 cm in diameter. Passes in the spinal canal. Inside it is the spinal canal filled with fluid. Gray matter is located inside, white - outside. Passes into the brain stem, forming a single system
Functions	Carries out the highest nervous activity(thinking, speech, second signaling system, memory, imagination, ability to write, read). Communication with the external environment occurs with the help of analyzers located in the occipital lobe (visual zone), in the temporal lobe (auditory zone), along the central sulcus (musculoskeletal zone) and on the inner surface of the cortex (gustatory and olfactory zones). Regulates the work of the whole organism through the peripheral nervous system	Regulates and coordinates body movements muscle tone. Carries out unconditioned reflex activity (centers of innate reflexes)	Connects the brain with the spinal cord into a single central nervous system. In the medulla oblongata there are centers: respiratory, digestive, cardiovascular. The bridge connects both halves of the cerebellum. The midbrain controls reactions to external stimuli, muscle tone (tension). The diencephalon regulates metabolism, body temperature, connects body receptors with the cerebral cortex	Operates under the control of the brain. Arcs of unconditioned (innate) reflexes pass through it, excitation and inhibition during movement. Pathways - white matter connecting the brain to the spinal cord; is a conductor of nerve impulses. Regulates the work of internal organs through the peripheral nervous system Through the spinal nerves, voluntary movements of the body are controlled

PERIPHERAL NERVOUS SYSTEM

The peripheral nervous system is formed by nerves emerging from the central nervous system, and nerve nodes and plexuses located mainly near the brain and spinal cord, as well as next to various internal organs or in the wall of these organs. In the peripheral nervous system, somatic and autonomic divisions are distinguished.

somatic nervous system

This system is formed by sensory nerve fibers that go to the central nervous system from various receptors, and motor nerve fibers that innervate skeletal muscles. Characteristic features fibers of the somatic nervous system is that they are not interrupted anywhere from the central nervous system to the receptor or skeletal muscle, they have a relatively large diameter and a high speed of excitation. These fibers make up most of the nerves that emerge from the CNS and form the peripheral nervous system.

There are 12 pairs of cranial nerves that emerge from the brain. The characteristics of these nerves are given in Table 1. [show] .

Table 1. Cranial nerves

Pair	Name and composition of the nerve	The exit point of the nerve from the brain	Function
I	Olfactory	Large hemispheres of the forebrain	Transmits excitation (sensory) from the olfactory receptors to the olfactory center
II	visual (sensory)	diencephalon	Transmits excitation from retinal receptors to the visual center
III	Oculomotor (motor)	midbrain	Innervates the eye muscles, provides eye movements
IV	Block (motor)	Same	Same
V	Trinity (mixed)	Bridge and medulla oblongata	Transmits excitation from the receptors of the skin of the face, mucous membranes of the lips, mouth and teeth, innervates the masticatory muscles
VI	Abductor (motor)	Medulla	Innervates the rectus lateral muscle of the eye, causes eye movement to the side
VII	Facial (mixed)	Same	Transmits excitation from the taste buds of the tongue and oral mucosa to the brain, innervates the mimic muscles and salivary glands
VIII	auditory (sensitive)	Same	Transmits stimulation from inner ear receptors
IX	Glossopharyngeal (mixed)	Same	Transmits excitation from taste buds and pharyngeal receptors, innervates the muscles of the pharynx and salivary glands
X	Wandering (mixed)	Same	Innervates the heart, lungs, most of the abdominal organs, transmits excitation from the receptors of these organs to the brain and centrifugal impulses to reverse direction
XI	Additional (motor)	Same	Innervates the muscles of the neck and neck, regulates their contractions
XII	Hyoid (motor)	Same	Innervates the muscles of the tongue and neck, causes their contraction

Each segment of the spinal cord gives off one pair of nerves containing sensory and motor fibers. All sensory, or centripetal, fibers enter the spinal cord through the posterior roots, on which there are thickenings - nerve nodes. In these nodes are the bodies of centripetal neurons.

The fibers of the motor, or centrifugal, neurons exit the spinal cord through the anterior roots. Each segment of the spinal cord corresponds to a certain part of the body - metamere. However, the innervation of the metameres occurs in such a way that each pair of spinal nerves innervates three adjacent metameres, and each metamere is innervated by three adjacent segments of the spinal cord. Therefore, in order to completely denervate any metamere of the body, it is necessary to cut the nerves of three neighboring segments of the spinal cord.

The autonomic nervous system is a section of the peripheral nervous system that innervates internal organs: the heart, stomach, intestines, kidneys, liver, etc. It does not have its own special sensitive pathways. Sensitive impulses from organs are transmitted through sensory fibers, which also pass through the peripheral nerves, are common to the somatic and autonomic nervous systems, but make up a smaller part of them.

Unlike the somatic nervous system, autonomic nerve fibers are thinner and conduct excitation much more slowly. On the way from the central nervous system to the innervated organ, they are necessarily interrupted with the formation of a synapse.

Thus, the centrifugal pathway in the autonomic nervous system includes two neurons - preganglionic and postganglionic. The body of the first neuron is located in the central nervous system, and the body of the second is outside it, in the nerve nodes (ganglia). There are many more postganglionic neurons than preganglionic ones. As a result, each preganglionic fiber in the ganglion fits and transmits its excitation to many (10 or more) postganglionic neurons. This phenomenon is called animation.

According to a number of signs, the sympathetic and parasympathetic divisions are distinguished in the autonomic nervous system.

Sympathetic department The autonomic nervous system is formed by two sympathetic chains of nerve nodes (paired border trunk - vertebral ganglia), located on both sides of the spine, and nerve branches that depart from these nodes and go to all organs and tissues as part of mixed nerves. The nuclei of the sympathetic nervous system are located in the lateral horns of the spinal cord, from the 1st thoracic to the 3rd lumbar segments.

The impulses coming through the sympathetic fibers to the organs provide reflex regulation of their activity. In addition to the internal organs, sympathetic fibers innervate blood vessels in them, as well as in the skin and skeletal muscles. They increase and speed up heart contractions, cause a rapid redistribution of blood by constricting some vessels and expanding others.

Parasympathetic department represented by a number of nerves, among which the vagus nerve is the largest. It innervates almost all organs of the chest and abdominal cavity.

The nuclei of the parasympathetic nerves lie in the middle, oblong sections of the brain and sacral spinal cord. Unlike the sympathetic nervous system, all parasympathetic nerves reach the peripheral nerve nodes located in the internal organs or on the outskirts of them. The impulses carried out by these nerves cause weakening and slowing of cardiac activity, narrowing of the coronary vessels of the heart and brain vessels, dilation of the vessels of the salivary and other digestive glands, which stimulates the secretion of these glands, and increases the contraction of the muscles of the stomach and intestines.

The main differences between the sympathetic and parasympathetic divisions of the autonomic nervous system are given in Table. 2. [show] .

Table 2. Autonomic nervous system

Index	Sympathetic nervous system	parasympathetic nervous system
Location of the pregangloonic neuron	Thoracic and lumbar spinal cord	Brain stem and sacral spinal cord
Location of switch to postganglionic neuron	Nerve nodes of the sympathetic chain	Nerves in internal organs or near organs
Postganglionic neuron mediator	Norepinephrine	Acetylcholine
Physiological action	Stimulates the work of the heart, constricts blood vessels, enhances the performance of skeletal muscles and metabolism, inhibits the secretory and motor activity of the digestive tract, relaxes the walls of the bladder	It slows down the work of the heart, dilates some blood vessels, enhances the secretion of juice and motor activity of the digestive tract, causes contraction of the walls of the bladder

Most of the internal organs receive a double autonomic innervation, that is, both sympathetic and parasympathetic nerve fibers approach them, which function in close interaction, having the opposite effect on the organs. It has great importance in the adaptation of the body to constantly changing environmental conditions.

A significant contribution to the study of the autonomic nervous system was made by L. A. Orbeli [show] .

Orbeli Leon Abgarovich (1882-1958) - Soviet physiologist, student of I.P. Pavlov. Acad. Academy of Sciences of the USSR, Academy of Sciences of the ArmSSR and the Academy of Medical Sciences of the USSR. Head of the Military Medical Academy, Institute of Physiology. I, P. Pavlov of the USSR Academy of Sciences, Institute of Evolutionary Physiology, Vice-President of the USSR Academy of Sciences.

The main direction of research is the physiology of the autonomic nervous system.

L. A. Orbeli created and developed the doctrine of the adaptive-trophic function of the sympathetic nervous system. He also carried out research on the coordination of the activity of the spinal cord, on the physiology of the cerebellum, and on higher nervous activity.

Nervous system	Peripheral nervous system
	somatic (nerve fibers are not interrupted; impulse conduction speed is 30-120 m/s)		vegetative (nerve fibers are interrupted by nodes: the speed of the impulse is 1-3 m / s)
	cranial nerves (12 pairs)	spinal nerves (31 pairs)	sympathetic nerves	parasympathetic nerves
Composition and structure	Depart from various parts of the brain in the form of nerve fibers. Subdivided into centripetal, centrifugal. Innervate the sense organs, internal organs, skeletal muscles	They depart in symmetrical pairs on both sides of the spinal cord. The processes of centripetal neurons enter through the posterior roots; processes of centrifugal neurons exit through the anterior roots. The processes join to form a nerve	They depart in symmetrical pairs on both sides of the spinal cord in the thoracic and lumbar regions. The prenodal fiber is short, as the nodes lie along the spinal cord; the post-nodal fiber is long, as it goes from the node to the innervated organ	Depart from the brain stem and sacral spinal cord. Nerve nodes lie in the walls of or near the innervated organs. The prenodal fiber is long, as it passes from the brain to the organ, the postnodal fiber is short, as it is located in the innervated organ
Functions	They provide communication of the body with the external environment, quick reactions to its change, orientation in space, body movements (purposeful), sensitivity, vision, hearing, smell, touch, taste, facial expressions, speech. Activities are controlled by the brain	Carry out movements of all parts of the body, limbs, determine the sensitivity of the skin. They innervate skeletal muscles, causing voluntary and involuntary movements. Voluntary movements are carried out under the control of the brain, involuntary under the control of the spinal cord (spinal reflexes)	Innervate internal organs. Post-nodal fibers leave the spinal cord as part of the mixed nerve and pass to the internal organs. Nerves form plexuses - solar, pulmonary, cardiac. Stimulate the work of the heart, sweat glands, metabolism. They hinder the activity of the digestive tract, constrict blood vessels, relax the walls of the bladder, dilate the pupils, etc.	They innervate the internal organs, exerting an influence on them opposite to the action of the sympathetic nervous system. The largest nerve is the vagus. Its branches are located in many internal organs - the heart, blood vessels, stomach, since the nodes of this nerve are located there.
			The activity of the autonomic nervous system regulates the work of all internal organs, adapting them to the needs of the whole organism.

CNS - central nervous system- the main part of the nervous system of all animals, including humans, consisting of an accumulation of nerve cells (neurons) and their processes; in invertebrates it is represented by a system of closely interconnected nerve nodes (ganglia), in vertebrates - by the spinal cord and brain.

central nervous system(CNS), when considered in detail, consists of the forebrain, midbrain, hindbrain and spinal cord. In these main sections of the central nervous system, in turn, the most important structures are distinguished that are directly related to mental processes, states and properties of a person: the thalamus, hypothalamus, bridge, cerebellum and medulla oblongata.

Main and specific function CNS- the implementation of simple and complex highly differentiated reflective reactions, called reflexes. In higher animals and humans, the lower and middle sections of the central nervous system - the spinal cord, medulla oblongata, midbrain, diencephalon and cerebellum - regulate the activity of individual organs and systems of a highly developed organism, communicate and interact between them, ensure the unity of the organism and the integrity of its activity. Superior department CNS- the cerebral cortex and the nearest subcortical formations - mainly regulates the connection and relationship of the body as a whole with the environment.
Almost all departments of the central and peripheral nervous system are involved in the processing of information coming through external and internal receptors located on the periphery of the body and in the organs themselves. The work of the cerebral cortex and subcortical structures included in the forebrain is associated with higher mental functions, with thinking and consciousness of a person.

The central nervous system is connected to all organs and tissues of the body through nerves that come out of the brain and spinal cord. They carry information that enters the brain from the external environment and conduct it in the opposite direction to individual parts and organs of the body. Nerve fibers entering the brain from the periphery are called afferent, and those that conduct impulses from the center to the periphery are called efferent.
central nervous system is a collection of nerve cells - neurons. CNS neurons form many circuits that perform two main functions: they provide reflex activity, as well as complex information processing in higher brain centers. These higher centers, such as the visual cortex ( visual cortex), receive incoming information, process it and transmit a response signal along the axons.
Tree-like processes extending from the bodies of nerve cells are called dendrites. One of these processes is elongated and connects the bodies of some neurons with the bodies or dendrites of other neurons. It's called an axon. Part of the axons is covered with a special myelin sheath, which contributes to faster conduction of the impulse along the nerve.
The places where nerve cells meet each other are called synapses. Through them, nerve impulses are transmitted from one cell to another. The mechanism of synaptic impulse transmission, which operates on the basis of biochemical metabolic processes, can facilitate or hinder the passage of nerve impulses through the central nervous system and thereby participate in the regulation of many mental processes and conditions of the body.

CNS connected with all organs and tissues through the peripheral nervous system, which in vertebrates includes cranial nerves extending from the brain, and spinal nerves - from the spinal cord, intervertebral nerve nodes, as well as the peripheral part of the autonomic nervous system - nerve nodes, with suitable to them (preganglionic) and outgoing from them (postganglionic) nerve fibers. Sensitive, or afferent, nerve adductor fibers carry excitation to the central nervous system from peripheral receptors; along the efferent efferent (motor and autonomic) nerve fibers, excitation from the central nervous system is directed to the cells of the executive working apparatus (muscles, glands, blood vessels, etc.). In all departments CNS there are afferent neurons that perceive stimuli coming from the periphery, and efferent neurons that send nerve impulses to the periphery to various executive effector organs. Afferent and efferent cells, with their processes, can contact each other and form a two-neuron reflex arc that performs elementary reflexes (for example, tendon reflexes of the spinal cord). But, as a rule, interneurons, or interneurons, are located in the reflex arc between the afferent and efferent neurons. Communication between different parts of the CNS is also carried out with the help of many processes of afferent, efferent and intercalary neurons of these parts, which form intracentral short and long pathways. Part CNS also includes neuroglial cells that perform a supporting function in it, and also participate in the metabolism of nerve cells.

NERVOUS SYSTEM, a very complex network of structures that permeates the entire body and provides self-regulation of its vital activity due to the ability to respond to external and internal influences (stimuli). The main functions of the nervous system are the receipt, storage and processing of information from the external and internal environment, the regulation and coordination of the activities of all organs and organ systems. In humans, as in mammals, the nervous system includes three main components: 1) nerve cells (neurons); 2) glial cells associated with them, in particular neuroglial cells, as well as cells that form neurilemma; 3) connective tissue. Neurons provide the conduction of nerve impulses; neuroglia performs supporting, protective and trophic functions both in the brain and spinal cord, and neurilemma, which consists mainly of specialized, so-called. Schwann cells, participates in the formation of sheaths of peripheral nerve fibers; connective tissue supports and links together the various parts of the nervous system.

The human nervous system is divided in different ways. Anatomically, it consists of the central nervous system ( CNS) and the peripheral nervous system (PNS). CNS includes the brain and spinal cord, and the PNS, which provides communication between the CNS and various parts bodies - cranial and spinal nerves, as well as nerve nodes (ganglia) and nerve plexuses that lie outside the spinal cord and brain.
Neuron. The structural and functional unit of the nervous system is a nerve cell - a neuron. It is estimated that there are more than 100 billion neurons in the human nervous system. A typical neuron consists of a body (i.e., a nuclear part) and processes, one usually non-branching process, an axon, and several branching ones, dendrites. The axon carries impulses from the cell body to the muscles, glands, or other neurons, while the dendrites carry them to the cell body.
In a neuron, as in other cells, there is a nucleus and a number of tiny structures - organelles (see also

SOCIO-TECHNOLOGICAL INSTITUTE OF MOSCOW STATE SERVICE UNIVERSITY

ANATOMY OF THE CENTRAL NERVOUS SYSTEM

(Tutorial)

O.O. Yakymenko

Moscow - 2002

The manual on the anatomy of the nervous system is intended for students of the Socio-Technological Institute of the Faculty of Psychology. The content includes the main issues related to the morphological organization of the nervous system. In addition to anatomical data on the structure of the nervous system, the work includes histological cytological characteristics of the nervous tissue. As well as questions of information about the growth and development of the nervous system from embryonic to late postnatal ontogenesis.

For clarity of the material presented in the text, illustrations are included. For independent work students are given a list of educational and scientific literature, as well as anatomical atlases.

Classical scientific data on the anatomy of the nervous system are the foundation for studying the neurophysiology of the brain. Knowledge of the morphological characteristics of the nervous system at each stage of ontogenesis is necessary for understanding the age-related dynamics of behavior and the human psyche.

SECTION I. CYTOLOGICAL AND HISTOLOGICAL CHARACTERISTICS OF THE NERVOUS SYSTEM

General plan of the structure of the nervous system

The main function of the nervous system is to quickly and accurately transmit information, ensuring the relationship of the body with the outside world. Receptors respond to any signals from the external and internal environment, converting them into streams of nerve impulses that enter the central nervous system. Based on the analysis of the flow of nerve impulses, the brain forms an adequate response.

Together with the endocrine glands, the nervous system regulates the work of all organs. This regulation is carried out due to the fact that the spinal cord and brain are connected by nerves with all organs, bilateral connections. From the organs to the central nervous system, signals about their functional state are received, and the nervous system, in turn, sends signals to the organs, correcting their functions and providing all life processes - movement, nutrition, excretion, and others. In addition, the nervous system provides coordination of the activities of cells, tissues, organs and organ systems, while the body functions as a whole.

The nervous system is the material basis of mental processes: attention, memory, speech, thinking, etc., with the help of which a person not only cognizes the environment, but can also actively change it.

Thus, the nervous system is that part of the living system that specializes in the transmission of information and in the integration of reactions in response to environmental influences.

Central and peripheral nervous system

The nervous system is divided topographically into the central nervous system, which includes the brain and spinal cord, and the peripheral, which consists of nerves and ganglia.

Nervous system

According to the functional classification, the nervous system is divided into somatic (sections of the nervous system that regulate the work of skeletal muscles) and autonomous (vegetative), which regulates the work of internal organs. The autonomic nervous system is divided into two divisions: sympathetic and parasympathetic.

Nervous system

somatic autonomous

sympathetic parasympathetic

Both the somatic and autonomic nervous systems include a central and peripheral divisions.

nervous tissue

The main tissue from which the nervous system is formed is nervous tissue. It differs from other types of tissue in that it lacks intercellular substance.

Nervous tissue is made up of two types of cells: neurons and glial cells. Neurons play a major role in providing all the functions of the central nervous system. Glial cells are of auxiliary importance, performing supporting, protective, trophic functions, etc. On average, the number of glial cells exceeds the number of neurons by a ratio of 10:1, respectively.

The shells of the brain are formed by connective tissue, and the cavities of the brain are formed by a special type of epithelial tissue (epindymal lining).

Neuron - structural and functional unit of the nervous system

The neuron has features common to all cells: it has a shell-plasmatic membrane, a nucleus and cytoplasm. The membrane is a three-layer structure containing lipid and protein components. In addition, there is a thin layer on the surface of the cell called the glycocalys. The plasma membrane regulates the exchange of substances between the cell and the environment. For a nerve cell, this is especially important, since the membrane regulates the movement of substances that are directly related to nerve signaling. The membrane also serves as the site of electrical activity underlying rapid neural signaling and the site of action for peptides and hormones. Finally, its sections form synapses - the place of contact of cells.

Each nerve cell has a nucleus that contains genetic material in the form of chromosomes. The nucleus performs two important functions - it controls the differentiation of the cell into its final form, determining the types of connections and regulates protein synthesis throughout the cell, controlling the growth and development of the cell.

In the cytoplasm of a neuron there are organelles (endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, ribosomes, etc.).

Ribosomes synthesize proteins, some of which remain in the cell, the other part is intended for removal from the cell. In addition, ribosomes produce elements of the molecular apparatus for most cellular functions: enzymes, carrier proteins, receptors, membrane proteins, etc.

The endoplasmic reticulum is a system of channels and spaces surrounded by a membrane (large, flat, called cisterns, and small, called vesicles or vesicles). A smooth and rough endoplasmic reticulum is distinguished. The latter contains ribosomes

The function of the Golgi apparatus is to store, concentrate and package secretory proteins.

In addition to systems that produce and transfer different substances, the cell has an internal digestive system, consisting of lysosomes that do not have a specific shape. They contain a variety of hydrolytic enzymes that break down and digest many compounds that occur both inside and outside the cell.

Mitochondria are the most complex cell organelle after the nucleus. Its function is the production and delivery of energy necessary for the vital activity of cells.

Most of the body's cells are able to absorb various sugars, while energy is either released or stored in the cell in the form of glycogen. However, nerve cells in the brain use only glucose, since all other substances are trapped by the blood-brain barrier. Most of them lack the ability to store glycogen, which increases their dependence on blood glucose and oxygen for energy. Therefore, nerve cells have the largest number of mitochondria.

The neuroplasm contains special-purpose organelles: microtubules and neurofilaments, which differ in size and structure. Neurofilaments are found only in nerve cells and represent the inner skeleton of the neuroplasm. Microtubules stretch along the axon along the internal cavities from the soma to the end of the axon. These organelles distribute biologically active substances (Fig. 1 A and B). Intracellular transport between the cell body and outgoing processes can be retrograde - from the nerve endings to the cell body and orthograde - from the cell body to the endings.

Rice. 1 A. Internal structure of a neuron

A distinctive feature of neurons is the presence of mitochondria in the axon as an additional source of energy and neurofibrils. Adult neurons are incapable of dividing.

Each neuron has an extended central part of the body - the soma and processes - dendrites and an axon. The cell body is enclosed in a cell membrane and contains the nucleus and nucleolus, maintaining the integrity of the membranes of the cell body and its processes, which ensure the conduction of nerve impulses. In relation to the processes, the soma performs a trophic function, regulating the metabolism of the cell. Through dendrites (afferent processes) impulses arrive to the body of the nerve cell, and through axons (efferent processes) from the body of the nerve cell to other neurons or organs

Most of the dendrites (dendron - tree) are short, strongly branching processes. Their surface is significantly increased due to small outgrowths - spines. Axon (axis - process) is often a long, slightly branching process.

Each neuron has only one axon, the length of which can reach several tens of centimeters. Sometimes lateral processes - collaterals - depart from the axon. The endings of the axon, as a rule, branch and are called terminals. The place where the axon departs from the cell soma is called the axonal hillock.

Rice. 1 B. External structure of a neuron

There are several classifications of neurons based on different characteristics: the shape of the soma, the number of processes, the functions and effects that a neuron has on other cells.

Depending on the shape of the soma, granular (ganglion) neurons are distinguished, in which the soma has a rounded shape; pyramidal neurons of different sizes - large and small pyramids; stellate neurons; spindle-shaped neurons (Fig. 2 A).

According to the number of processes, unipolar neurons are distinguished, having one process extending from the cell soma; pseudounipolar neurons (such neurons have a T-shaped branching process); bipolar neurons, which have one dendrite and one axon; and multipolar neurons, which have several dendrites and one axon (Fig. 2B).

Rice. 2. Classification of neurons according to the shape of the soma, according to the number of processes

Unipolar neurons are located in sensory nodes (for example, spinal, trigeminal) and are associated with such types of sensitivity as pain, temperature, tactile, pressure, vibration, etc.

These cells, although called unipolar, actually have two processes that fuse near the cell body.

Bipolar cells are characteristic of the visual, auditory and olfactory systems

Multipolar cells have a variety of body shapes - spindle-shaped, basket-shaped, stellate, pyramidal - small and large.

According to the functions performed, neurons are: afferent, efferent and intercalary (contact).

Afferent neurons are sensory (pseudo-unipolar), their somas are located outside the central nervous system in the ganglia (spinal or cranial). The shape of the soma is granular. Afferent neurons have one dendrite that fits to receptors (skin, muscles, tendons, etc.). Through dendrites, information about the properties of stimuli is transmitted to the soma of the neuron and along the axon to the central nervous system.

Efferent (motor) neurons regulate the work of effectors (muscles, glands, tissues, etc.). These are multipolar neurons, their somas are stellate or pyramidal in shape, lying in the spinal cord or brain or in the ganglia of the autonomic nervous system. Short, abundantly branching dendrites receive impulses from other neurons, and long axons go beyond the central nervous system and, as part of the nerve, go to effectors (working organs), for example, to the skeletal muscle.

Intercalary neurons (interneurons, contact) make up the bulk of the brain. They carry out communication between afferent and efferent neurons, process information coming from receptors to the central nervous system. Basically, these are multipolar stellate neurons.

Among the intercalary neurons, there are neurons with long and short axons (Fig. 3 A, B).

As sensory neurons are shown: a neuron, the process of which is part of the auditory fibers of the vestibulocochlear nerve (VIII pair), a neuron that responds to skin stimulation (SN). Interneurons are represented by amacrine (AmN) and bipolar (BN) retinal cells, olfactory bulb neuron (OBN), locus coeruleus neuron (PCN), pyramidal cell of the cerebral cortex (PN), and stellate neuron (SN) of the cerebellum. The motoneuron of the spinal cord is shown as a motor neuron.

Rice. 3 A. Classification of neurons according to their functions

Sensory neuron:

1 - bipolar, 2 - pseudo-bipolar, 3 - pseudo-unipolar, 4 - pyramidal cell, 5 - neuron of the spinal cord, 6 - neuron of n. ambiguus, 7 - neuron of the nucleus of the hypoglossal nerve. Sympathetic neurons: 8 - from the stellate ganglion, 9 - from the superior cervical ganglion, 10 - from the intermediolateral column of the lateral horn of the spinal cord. Parasympathetic neurons: 11 - from the node of the muscular plexus of the intestinal wall, 12 - from the dorsal nucleus of the vagus nerve, 13 - from the ciliary node.

According to the effect that neurons have on other cells, excitatory neurons and inhibitory neurons are distinguished. Excitatory neurons have an activating effect, increasing the excitability of the cells with which they are associated. Inhibitory neurons, on the contrary, reduce the excitability of cells, causing a depressant effect.

The space between neurons is filled with cells called neuroglia (the term glia means glue, the cells “glue” the components of the central nervous system into a single whole). Unlike neurons, neuroglial cells divide throughout a person's life. There are a lot of neuroglial cells; in some parts of the nervous system there are 10 times more of them than nerve cells. Macroglial cells and microglial cells are isolated (Fig. 4).

Four main types of glial cells.

A neuron surrounded by various glia elements

1 - macroglia astrocytes

2 - macroglia oligodendrocytes

3 - microglia macroglia

Rice. 4. Macroglial and microglial cells

Macroglia include astrocytes and oligodendrocytes. Astrocytes have many processes that radiate from the cell body in all directions, giving the appearance of a star. In the central nervous system, some processes terminate in a terminal stalk on the surface of blood vessels. Astrocytes lying in the white matter of the brain are called fibrous astrocytes due to the presence of many fibrils in the cytoplasm of their bodies and branches. In the gray matter, astrocytes contain fewer fibrils and are called protoplasmic astrocytes. They serve as a support for nerve cells, provide repair of nerves after damage, isolate and unite nerve fibers and endings, participate in metabolic processes that simulate the ionic composition, mediators. The assumptions that they are involved in the transport of substances from blood vessels to nerve cells and form part of the blood-brain barrier have now been rejected.

1. Oligodendrocytes are smaller than astrocytes, contain small nuclei, are more common in the white matter, and are responsible for the formation of myelin sheaths around long axons. They act as an insulator and increase the speed of nerve impulses along the processes. The myelin sheath is segmental, the space between the segments is called the node of Ranvier (Fig. 5). Each of its segments, as a rule, is formed by one oligodendrocyte (Schwann cell), which, becoming thinner, twists around the axon. The myelin sheath has a white color (white matter), since the composition of the membranes of oligodendrocytes includes a fat-like substance - myelin. Sometimes one glial cell, forming outgrowths, takes part in the formation of segments of several processes. It is assumed that oligodendrocytes carry out a complex metabolic exchange with nerve cells.

1 - oligodendrocyte, 2 - connection between the glial cell body and the myelin sheath, 4 - cytoplasm, 5 - plasma membrane, 6 - interception of Ranvier, 7 - loop of the plasma membrane, 8 - mesaxon, 9 - scallop

Rice. 5A. Participation of the oligodendrocyte in the formation of the myelin sheath

Four stages of "envelopment" of the axon (2) by the Schwann cell (1) and its wrapping by several double layers of the membrane are presented, which, after compression, form a dense myelin sheath.

Rice. 5 B. Diagram of the formation of the myelin sheath.

The neuron's soma and dendrites are covered with thin sheaths that do not form myelin and constitute gray matter.

2. Microglia are represented by small cells capable of amoeboid locomotion. The function of microglia is to protect neurons from inflammation and infections (according to the mechanism of phagocytosis - the capture and digestion of genetically alien substances). Microglial cells deliver oxygen and glucose to neurons. In addition, they are part of the blood-brain barrier, which is formed by them and endothelial cells that form the walls of blood capillaries. The blood-brain barrier traps macromolecules, limiting their access to neurons.

Nerve fibers and nerves

Long processes of nerve cells are called nerve fibers. Through them, nerve impulses can be transmitted over long distances up to 1 meter.

The classification of nerve fibers is based on morphological and functional features.

Nerve fibers that have a myelin sheath are called myelinated (pulp), and fibers that do not have a myelin sheath are called unmyelinated (pulpless).

According to functional features, afferent (sensory) and efferent (motor) nerve fibers are distinguished.

Nerve fibers that extend beyond the nervous system form nerves. A nerve is a collection of nerve fibers. Each nerve has a sheath and blood supply (Fig. 6).

1 - common nerve trunk, 2 - nerve fiber ramifications, 3 - nerve sheath, 4 - bundles of nerve fibers, 5 - myelin sheath, 6 - Schwan cell membrane, 7 - Ranvier intercept, 8 - Schwan cell nucleus, 9 - axolemma.

Rice. 6 Structure of a nerve (A) and nerve fiber (B).

There are spinal nerves associated with the spinal cord (31 pairs) and cranial nerves (12 pairs) associated with the brain. Depending on the quantitative ratio of afferent and efferent fibers in one nerve, sensory, motor and mixed nerves are distinguished. Afferent fibers predominate in sensory nerves, efferent fibers predominate in motor nerves, and the quantitative ratio of afferent and efferent fibers is approximately equal in mixed nerves. All spinal nerves are mixed nerves. Among the cranial nerves, there are three types of nerves listed above. I pair - olfactory nerves (sensory), II pair - optic nerves (sensory), III pair - oculomotor (motor), IV pair - trochlear nerves (motor), V pair - trigeminal nerves (mixed), VI pair - abducens nerves ( motor), VII pair - facial nerves (mixed), VIII pair - vestibulo-cochlear nerves (mixed), IX pair - glossopharyngeal nerves (mixed), X pair - vagus nerves (mixed), XI pair - accessory nerves (motor), XII pair - hypoglossal nerves (motor) (Fig. 7).

I - pair - olfactory nerves,

II - para-optic nerves,

III - para-oculomotor nerves,

IV - paratrochlear nerves,

V - pair - trigeminal nerves,

VI - para-abducens nerves,

VII - parafacial nerves,

VIII - para-cochlear nerves,

IX - para-glossopharyngeal nerves,

X - pair - vagus nerves,

XI - para-accessory nerves,

XII - pair-1,2,3,4 - roots of the upper spinal nerves.

Rice. 7, Diagram of location of cranial and spinal nerves

Gray and white matter of the nervous system

Fresh sections of the brain show that some structures are darker - this is the gray matter of the nervous system, while other structures are lighter - the white matter of the nervous system. The white matter of the nervous system is formed by myelinated nerve fibers, the gray matter is formed by unmyelinated parts of the neuron - soma and dendrites.

The white matter of the nervous system is represented by central tracts and peripheral nerves. The function of white matter is the transmission of information from receptors to the central nervous system and from one part of the nervous system to another.

The gray matter of the central nervous system is formed by the cerebellar cortex and the cortex of the cerebral hemispheres, nuclei, ganglia and some nerves.

The nuclei are accumulations of gray matter in the thickness of the white matter. They are located in different parts of the central nervous system: in the white matter of the cerebral hemispheres - subcortical nuclei, in the white matter of the cerebellum - cerebellar nuclei, some nuclei are located in the intermediate, middle and medulla oblongata. Most of the nuclei are nerve centers that regulate one or another function of the body.

Ganglia are a collection of neurons located outside the central nervous system. There are spinal, cranial ganglia and ganglia of the autonomic nervous system. Ganglia are formed mainly by afferent neurons, but they may include intercalary and efferent neurons.

Interaction of neurons

The place of functional interaction or contact of two cells (the place where one cell influences another cell) was called the synapse by the English physiologist C. Sherrington.

Synapses are either peripheral or central. An example of a peripheral synapse is the neuromuscular junction when a neuron makes contact with a muscle fiber. Synapses in the nervous system are called central when two neurons are in contact. Five types of synapses are distinguished, depending on which parts the neurons contact: 1) axo-dendritic (the axon of one cell contacts the dendrite of another); 2) axo-somatic (the axon of one cell contacts the soma of another cell); 3) axo-axonal (the axon of one cell contacts the axon of another cell); 4) dendro-dendritic (the dendrite of one cell is in contact with the dendrite of another cell); 5) somo-somatic (somes of two cells contact). The bulk of the contacts are axo-dendritic and axo-somatic.

Synaptic contacts can be between two excitatory neurons, two inhibitory neurons, or between excitatory and inhibitory neurons. In this case, the neurons that have an effect are called presynaptic, and the neurons that are affected are called postsynaptic. The presynaptic excitatory neuron increases the excitability of the postsynaptic neuron. In this case, the synapse is called excitatory. The presynaptic inhibitory neuron has the opposite effect - it reduces the excitability of the postsynaptic neuron. Such a synapse is called inhibitory. Each of the five types of central synapses has its own morphological features, although the general scheme of their structure is the same.

The structure of the synapse

Consider the structure of the synapse on the example of axo-somatic. The synapse consists of three parts: the presynaptic ending, the synaptic cleft and the postsynaptic membrane (Fig. 8 A, B).

A- Synaptic inputs of the neuron. Synaptic plaques of the endings of presynaptic axons form connections on the dendrites and body (some) of the postsynaptic neuron.

Rice. 8 A. The structure of synapses

The presynaptic ending is an extended part of the axon terminal. The synaptic cleft is the space between two contacting neurons. The diameter of the synaptic cleft is 10-20 nm. The membrane of the presynaptic ending facing the synaptic cleft is called the presynaptic membrane. The third part of the synapse is the postsynaptic membrane, which is located opposite the presynaptic membrane.

The presynaptic ending is filled with vesicles (vesicles) and mitochondria. Vesicles contain biologically active substances - mediators. Mediators are synthesized in the soma and transported via microtubules to the presynaptic ending. Most often, adrenaline, noradrenaline, acetylcholine, serotonin, gamma-aminobutyric acid (GABA), glycine and others act as a mediator. Usually, the synapse contains one of the mediators in a larger amount compared to other mediators. According to the type of mediator, it is customary to designate synapses: adrenoergic, cholinergic, serotonergic, etc.

The postsynaptic membrane contains special protein molecules- receptors that can attach molecules of mediators.

The synaptic cleft is filled with intercellular fluid, which contains enzymes that contribute to the destruction of neurotransmitters.

On one postsynaptic neuron there can be up to 20,000 synapses, some of which are excitatory, and some are inhibitory (Fig. 8 B).

B. Diagram of neurotransmitter release and processes occurring in a hypothetical central synapse.

Rice. 8 B. The structure of synapses

Apart from chemical synapses, in which mediators participate in the interaction of neurons, electrical synapses are found in the nervous system. In electrical synapses, the interaction of two neurons is carried out through biocurrents. Chemical stimuli predominate in the central nervous system.

In some interneurons, synapses, electrical and chemical transmission occurs simultaneously - this is a mixed type of synapses.

The influence of excitatory and inhibitory synapses on the excitability of the postsynaptic neuron is summed up and the effect depends on the location of the synapse. The closer the synapses are to the axonal hillock, the more efficient they are. On the contrary, the farther the synapses are located from the axonal hillock (for example, at the end of the dendrites), the less effective they are. Thus, synapses located on the soma and axonal hillock affect neuron excitability quickly and efficiently, while the influence of distant synapses is slow and smooth.

Neural networks

Thanks to synaptic connections, neurons are combined into functional units - neural networks. Neural networks can be formed by neurons located at a short distance. Such a neural network is called local. In addition, neurons remote from each other, from different areas of the brain, can be combined into a network. The highest level of organization of neuron connections reflects the connection of several areas of the central nervous system. This neural network is called through or system. There are descending and ascending paths. Information is transmitted along ascending pathways from the underlying areas of the brain to the overlying ones (for example, from the spinal cord to the cerebral cortex). Descending tracts connect the cerebral cortex with the spinal cord.

The most complex networks are called distribution systems. They are formed by neurons of different parts of the brain that control behavior, in which the body participates as a whole.

Some neural networks provide convergence (convergence) of impulses on a limited number of neurons. Neural networks can also be built according to the type of divergence (divergence). Such networks cause the transmission of information over considerable distances. In addition, neural networks provide integration (summation or generalization) of various kinds of information (Fig. 9).

Rice. 9. Nervous tissue.

A large neuron with many dendrites receives information through synaptic contact with another neuron (upper left). The myelinated axon forms a synaptic contact with the third neuron (below). Neuronal surfaces are shown without glial cells that surround the process directed towards the capillary (upper right).

Reflex as the basic principle of the nervous system

One example of a neural network would be the reflex arc needed to carry out the reflex. THEM. Sechenov in 1863 in his work “Reflexes of the Brain” developed the idea that the reflex is the basic principle of operation not only of the spinal cord, but also of the brain.

A reflex is a response of the body to irritation with the participation of the central nervous system. Each reflex has its own reflex arc - the path along which excitation passes from the receptor to the effector (executive organ). Any reflex arc consists of five components: 1) a receptor - a specialized cell designed to perceive a stimulus (sound, light, chemical, etc.), 2) an afferent path, which is represented by afferent neurons, 3) a section of the central nervous system , represented by the spinal cord or brain; 4) the efferent pathway consists of axons of efferent neurons that extend beyond the central nervous system; 5) effector - a working organ (muscle or gland, etc.).

The simplest reflex arc includes two neurons and is called monosynaptic (according to the number of synapses). A more complex reflex arc is represented by three neurons (afferent, intercalary and efferent) and is called three-neuron or disynaptic. However, most reflex arcs include a large number of intercalary neurons, and are called polysynaptic (Fig. 10 A, B).

Reflex arcs can pass only through the spinal cord (withdrawal of the hand when touching a hot object), or only the brain (closing of the eyelids with a jet of air directed at the face), or both through the spinal cord and through the brain.

Rice. 10A. 1 - intercalary neuron; 2 - dendrite; 3 - neuron body; 4 - axon; 5 - synapse between sensitive and intercalary neurons; 6 - axon of a sensitive neuron; 7 - body of a sensitive neuron; 8 - axon of a sensitive neuron; 9 - axon of a motor neuron; 10 - body of a motor neuron; 11 - synapse between intercalary and motor neurons; 12 - receptor in the skin; 13 - muscle; 14 - sympathetic gaglia; 15 - gut.

Rice. 10B. 1 - monosynaptic reflex arc, 2 - polysynaptic reflex arc, 3K - posterior spinal root, PC - anterior spinal root.

Rice. 10. Scheme of the structure of the reflex arc

Reflex arcs are closed in reflex rings with the help of feedback. concept feedback and its functional role were indicated by Bell in 1826. Bell wrote that two-way connections are established between the muscle and the central nervous system. With the help of feedback, signals about the functional state of the effector are sent to the central nervous system.

The morphological basis of the feedback is the receptors located in the effector and the afferent neurons associated with them. Thanks to feedback afferent connections, fine regulation of the effector and an adequate response of the body to changes in the environment is carried out.

Shells of the brain

The central nervous system (spinal cord and brain) has three connective tissue membranes: hard, arachnoid and soft. The outermost of them is the dura mater (it grows together with the periosteum lining the surface of the skull). The arachnoid lies under the hard shell. It is tightly pressed against the solid and there is no free space between them.

Directly adjacent to the surface of the brain is the pia mater, in which there are many blood vessels that feed the brain. Between the arachnoid and soft shells there is a space filled with liquid - liquor. The composition of the cerebrospinal fluid is close to blood plasma and intercellular fluid and plays a shockproof role. In addition, the cerebrospinal fluid contains lymphocytes that provide protection from foreign substances. He is also involved in the metabolism between the cells of the spinal cord, brain and blood (Fig. 11 A).

1 - dentate ligament, the process of which passes through the arachnoid membrane located laterally, 1a - dentate ligament attached to the dura mater of the spinal cord, 2 - arachnoid membrane, 3 - posterior root, passing in the canal formed by the soft and arachnoid membranes, Za - posterior root passing through a hole in the dura mater of the spinal cord, 36 - dorsal branches of the spinal nerve passing through the arachnoid, 4 - spinal nerve, 5 - spinal ganglion, 6 - hard shell spinal cord, 6a - dura mater turned to the side, 7 - pia mater of the spinal cord with the posterior spinal artery.

Rice. 11A. Meninges of the spinal cord

Cavities of the brain

Inside the spinal cord is the spinal canal, which, passing into the brain, expands in the medulla oblongata and forms the fourth ventricle. At the level of the midbrain, the ventricle passes into a narrow canal - the aqueduct of Sylvius. In the diencephalon, the aqueduct of Sylvius expands, forming a cavity of the third ventricle, which smoothly passes at the level of the cerebral hemispheres into the lateral ventricles (I and II). All of these cavities are also filled with CSF (Fig. 11 B)

Fig 11B. Scheme of the ventricles of the brain and their relationship to the surface structures of the cerebral hemispheres.

a - cerebellum, b - occipital pole, c - parietal pole, d - frontal pole, e - temporal pole, e - medulla oblongata.

1 - lateral opening of the fourth ventricle (Lushka's opening), 2 - lower horn of the lateral ventricle, 3 - plumbing, 4 - recessusinfundibularis, 5 - recrssusopticus, 6 - interventricular opening, 7 - anterior horn of the lateral ventricle, 8 - central part lateral ventricle, 9 - fusion of visual tubercles (massainter-melia), 10 - third ventricle, 11 -recessus pinealis, 12 - entrance to the lateral ventricle, 13 - posterior pro lateral ventricle, 14 - fourth ventricle.

Rice. 11. Shells (A) and cavities of the brain (B)

SECTION II. STRUCTURE OF THE CENTRAL NERVOUS SYSTEM

Spinal cord

The external structure of the spinal cord

The spinal cord is a flattened cord located in the spinal canal. Depending on the parameters of the human body, its length is 41–45 cm, its average diameter is 0.48–0.84 cm, and its weight is about 28–32 g. left half.

In front, the spinal cord passes into the brain, and behind it ends with a cerebral cone at the level of the 2nd vertebra of the lumbar spine. From the brain cone departs the connective tissue terminal thread (continuation of the terminal shells), which attaches the spinal cord to the coccyx. The terminal thread is surrounded by nerve fibers (cauda equina) (Fig. 12).

Two thickenings stand out on the spinal cord - cervical and lumbar, from which nerves depart, innervating, respectively, the skeletal muscles of the arms and legs.

In the spinal cord, cervical, thoracic, lumbar and sacral sections are distinguished, each of which is divided into segments: cervical - 8 segments, thoracic - 12, lumbar - 5, sacral 5-6 and 1 - coccygeal. Thus, the total number of segments is 31 (Fig. 13). Each segment of the spinal cord has paired spinal roots - anterior and posterior. Information from the receptors of the skin, muscles, tendons, ligaments, joints comes to the spinal cord through the posterior roots, therefore the posterior roots are called sensory (sensitive). Transection of the posterior roots turns off tactile sensitivity, but does not lead to loss of movement.

Rice. 12. Spinal cord.

a - front view (its ventral surface);

b - rear view (its dorsal surface).

The hard and arachnoid membranes are cut. The vascular membrane has been removed. Roman numerals indicate the order of the cervical (c), thoracic (th), lumbar (t)

and sacral(s) spinal nerves.

1 - cervical thickening

2 - spinal ganglion

3 - hard shell

4 - lumbar thickening

5 - cerebral cone

6 - terminal thread

Rice. 13. Spinal cord and spinal nerves (31 pairs).

Through the anterior roots of the spinal cord, nerve impulses enter the skeletal muscles of the body (with the exception of the muscles of the head), causing them to contract, therefore the anterior roots are called motor or motor. After transection of the anterior roots on one side, there is a complete shutdown of motor reactions, while sensitivity to touch or pressure is preserved.

The anterior and posterior roots of each side of the spinal cord unite to form the spinal nerves. The spinal nerves are called segmental, their number corresponds to the number of segments and is 31 pairs (Fig. 14)

The distribution of zones of the spinal nerves by segments was determined by determining the size and boundaries of the skin areas (dermatomes) innervated by each nerve. Dermatomes are located on the surface of the body according to the segmental principle. Cervical dermatomes include the back of the head, neck, shoulders, and anterior forearms. Thoracic sensory neurons innervate the remaining surface of the forearm, chest, and most of the abdomen. Sensory fibers from the lumbar, sacral, and coccygeal segments fit into the rest of the abdomen and legs.

Rice. 14. Scheme of dermatomes. Innervation of the body surface by 31 pairs of spinal nerves (C - cervical, T - thoracic, L - lumbar, S - sacral).

Internal structure of the spinal cord

The spinal cord is built according to the nuclear type. Around the spinal canal is gray matter, on the periphery - white. Gray matter is formed by soma of neurons and branching dendrites that do not have myelin sheaths. White matter is a collection of nerve fibers covered with myelin sheaths.

In the gray matter, the anterior and posterior horns are distinguished, between which lies the interstitial zone. There are lateral horns in the thoracic and lumbar regions of the spinal cord.

The gray matter of the spinal cord is formed by two groups of neurons: efferent and intercalary. The bulk of the gray matter is made up of intercalary neurons (up to 97%) and only 3% are efferent neurons or motor neurons. Motor neurons are located in the anterior horns of the spinal cord. Among them, a- and g-motor neurons are distinguished: a-motor neurons innervate skeletal muscle fibers and are large cells with relatively long dendrites; g-motor neurons are represented by small cells and innervate muscle receptors, increasing their excitability.

Intercalary neurons are involved in information processing, ensuring the coordinated work of sensory and motor neurons, and also connect the right and left halves of the spinal cord and its various segments (Fig. 15 A, B, C)

Rice. 15A. 1 - white matter of the brain; 2 - spinal canal; 3 - posterior longitudinal furrow; 4 - posterior root of the spinal nerve; 5 - spinal node; 6 - spinal nerve; 7 - gray matter of the brain; 8 - anterior root of the spinal nerve; 9 - anterior longitudinal furrow

Rice. 15B. Gray matter nuclei in the thoracic region

1,2,3 - sensitive nuclei of the posterior horn; 4, 5 - intercalary nuclei of the lateral horn; 6,7, 8,9,10 - motor nuclei of the anterior horn; I, II, III - anterior, lateral and posterior cords of the white matter.

The contacts between sensory, intercalary and motor neurons in the gray matter of the spinal cord are shown.

Rice. 15. Cross section of the spinal cord

Pathways of the spinal cord

The white matter of the spinal cord surrounds the gray matter and forms the columns of the spinal cord. Distinguish front, rear and side pillars. Pillars are tracts of the spinal cord formed by long axons of neurons going up towards the brain (ascending paths) or down from the brain to the lower segments of the spinal cord (descending paths).

The ascending pathways of the spinal cord carry information from receptors in the muscles, tendons, ligaments, joints, and skin to the brain. Ascending paths are also conductors of temperature and pain sensitivity. All ascending pathways cross at the level of the spinal (or brain) cord. Thus, the left half of the brain (the cerebral cortex and cerebellum) receive information from the receptors of the right half of the body and vice versa.

Main ascending paths: from mechanoreceptors of the skin and receptors of the musculoskeletal system - these are muscles, tendons, ligaments, joints - the bundles of Gaulle and Burdach, or, respectively, they are the same - tender and wedge-shaped bundles are represented by the posterior columns of the spinal cord.

From the same receptors, information enters the cerebellum along two pathways represented by the lateral columns, which are called the anterior and posterior spinal tracts. In addition, two more paths pass in the lateral columns - these are the lateral and anterior spinal thalamic paths, which transmit information from temperature and pain sensitivity receptors.

The posterior columns provide faster information about the localization of irritations than the lateral and anterior spinal thalamic pathways (Fig. 16 A).

1 - Gaulle's bundle, 2 - Burdach's bundle, 3 - dorsal spinal cerebellar tract, 4 - ventral spinal cerebellar tract. Neurons of group I-IV.

Rice. 16A. Ascending tracts of the spinal cord

descending paths, passing as part of the anterior and lateral columns of the spinal cord, are motor, as they affect the functional state of the skeletal muscles of the body. The pyramidal path begins mainly in the motor cortex of the hemispheres and passes to the medulla oblongata, where most of the fibers cross and pass to the opposite side. After that, the pyramidal path is divided into lateral and anterior bundles: respectively, the anterior and lateral pyramidal paths. Most of the pyramidal tract fibers terminate on interneurons, and about 20% form synapses on motor neurons. The pyramidal influence is exciting. Reticulo-spinal path, rubrospinal way and vestibulospinal the path (extrapyramidal system) begins, respectively, from the nuclei of the reticular formation, the brain stem, the red nuclei of the midbrain and the vestibular nuclei of the medulla oblongata. These pathways run in the lateral columns of the spinal cord, are involved in the coordination of movements and the provision of muscle tone. Extrapyramidal paths, as well as pyramidal ones, are crossed (Fig. 16 B).

The main descending spinal tracts of the pyramidal (lateral and anterior corticospinal tracts) and extra pyramidal (rubrospinal, reticulospinal and vestibulospinal tracts) systems.

Rice. 16 B. Scheme of pathways

Thus, the spinal cord performs two important functions: reflex and conduction. The reflex function is carried out due to the motor centers of the spinal cord: the motor neurons of the anterior horns ensure the work of the skeletal muscles of the body. At the same time, maintaining muscle tone, coordinating the work of the flexor-extensor muscles underlying movements and maintaining the constancy of the posture of the body and its parts is maintained (Fig. 17 A, B, C). Motoneurons located in the lateral horns of the thoracic segments of the spinal cord provide respiratory movements (inhale-exhale, regulating the work of the intercostal muscles). Motoneurons of the lateral horns of the lumbar and sacral segments represent the motor centers of smooth muscles that make up the internal organs. These are the centers of urination, defecation, and the work of the genital organs.

Rice. 17A. The arc of the tendon reflex.

Rice. 17B. Arcs of the flexion and cross extensor reflex.

Rice. 17V. Elementary scheme of unconditioned reflex.

Nerve impulses that occur when the receptor (p) is stimulated along afferent fibers (afferent nerve, only one such fiber is shown) go to the spinal cord (1), where they are transmitted through the intercalary neuron to efferent fibers (eff. nerve), through which they reach effector. Dashed lines - the spread of excitation from the lower parts of the central nervous system to its higher parts (2, 3,4) up to the cerebral cortex (5) inclusive. The resulting change in the state of the higher parts of the brain, in turn, affects (see arrows) the efferent neuron, affecting the final result of the reflex response.

Rice. 17. Reflex function of the spinal cord

The conduction function is performed by the spinal tracts (Fig. 18 A, B, C, D, E).

Rice. 18A. Back poles. This circuit, formed by three neurons, transmits information from pressure and touch receptors to the somatosensory cortex.

Rice. 18B. Lateral spinal thalamic tract. Along this path, information from temperature and pain receptors enters vast areas of the thoracic medulla.

Rice. 18V. Anterior dorsal thalamic tract. Along this path, information from pressure and touch receptors, as well as from pain and temperature receptors, enters the somatosensory cortex.

Rice. 18G. extrapyramidal system. Rubrospinal and reticulospinal pathways, which are part of the multineuronal extrapyramidal pathway that runs from the cerebral cortex to the spinal cord.

Rice. 18D. Pyramidal, or corticospinal, path

Rice. 18. Conduction function of the spinal cord

SECTION III. BRAIN.

General scheme of the structure of the brain (Fig. 19)

Brain

Figure 19A. Brain

1. Frontal cortex (cognitive area)

2. Motor cortex

3. Visual cortex

4. Cerebellum 5. Auditory cortex

Fig 19B. Side view

Figure 19B. The main formations of the medal surface of the brain on the mid-sagittal section.

Fig 19D. Inferior surface of the brain

Rice. 19. The structure of the brain

Hind brain

The hindbrain, including the medulla oblongata and the pons Varolii, is a phylogenetically ancient region of the central nervous system, retaining the features of a segmental structure. In the hindbrain, nuclei and ascending and descending pathways are localized. Afferent fibers from the vestibular and auditory receptors, from the receptors of the skin and muscles of the head, from the receptors of the internal organs, as well as from the higher structures of the brain, enter the hindbrain along the conducting paths. The nuclei of the V-XII pairs of cranial nerves are located in the hindbrain, some of which innervates the facial and oculomotor muscles.

Medulla

The medulla oblongata is located between the spinal cord, the pons and the cerebellum (Fig. 20). On the ventral surface of the medulla oblongata middle line the anterior median sulcus passes, on its sides there are two strands - pyramids, olives lie on the side of the pyramids (Fig. 20 A-B).

Rice. 20A. 1 - cerebellum 2 - cerebellar peduncles 3 - pons 4 - medulla oblongata

Rice. 20V. 1 - bridge 2 - pyramid 3 - olive 4 - anterior median fissure 5 - anterior lateral groove 6 - cross of the anterior funiculus 7 - anterior funiculus 8 - lateral funiculus

Rice. 20. Medulla oblongata

On the back side of the medulla oblongata stretches the posterior medial sulcus. On its sides lie the posterior cords, which go to the cerebellum as part of the hind legs.

Gray matter of the medulla oblongata

The nuclei of the four pairs of cranial nerves are located in the medulla oblongata. These include the nuclei of the glossopharyngeal, vagus, accessory, and hypoglossal nerves. In addition, the tender, sphenoid nuclei and cochlear nuclei of the auditory system, the nuclei of the lower olives and the nuclei of the reticular formation (giant cell, small cell and lateral), as well as the respiratory nuclei are isolated.

The nuclei of the hyoid (XII pair) and accessory (XI pair) nerves are motor, they innervate the muscles of the tongue and the muscles that move the head. The nuclei of the vagus (X pair) and glossopharyngeal (IX pair) nerves are mixed, they innervate the muscles of the pharynx, larynx, thyroid gland, and regulate swallowing and chewing. These nerves consist of afferent fibers coming from the receptors of the tongue, larynx, trachea and from the receptors of the internal organs of the chest and abdominal cavity. Efferent nerve fibers innervate the intestines, heart and blood vessels.

The nuclei of the reticular formation not only activate the cerebral cortex, supporting consciousness, but also form a respiratory center that provides respiratory movements.

Thus, part of the nuclei of the medulla oblongata regulates vital functions (these are the nuclei of the reticular formation and the nuclei of the cranial nerves). Another part of the nuclei is part of the ascending and descending tracts (tender and sphenoid nuclei, cochlear nuclei of the auditory system) (Fig. 21).

1-thin core;

2 - wedge-shaped nucleus;

3 - the end of the fibers of the posterior cords of the spinal cord;

4 - internal arcuate fibers - the second neuron of the cortical pathway;

5 - the intersection of the loops is located in the inter-shedding loop layer;

6 - medial loop - continuation of the internal arcuate ox

7 - a seam formed by a cross of loops;

8 - the core of the olive - the intermediate core of equilibrium;

9 - pyramidal paths;

10 - central channel.

Rice. 21. Internal structure of the medulla oblongata

White matter of the medulla oblongata

The white matter of the medulla oblongata is formed by long and short nerve fibers.

Long nerve fibers are part of the descending and ascending pathways. Short nerve fibers ensure the coordinated work of the right and left halves of the medulla oblongata.

pyramids medulla oblongata - part descending pyramidal tract, going to the spinal cord and ending in intercalary neurons and motor neurons. In addition, the rubro-spinal path passes through the medulla oblongata. The descending vestibulospinal and reticulospinal tracts originate in the medulla oblongata, respectively, from the vestibular and reticular nuclei.

The ascending spinal tracts pass through olives medulla oblongata and through the legs of the brain and transmit information from the receptors of the musculoskeletal system to the cerebellum.

gentle And wedge-shaped nuclei medulla oblongata are part of the spinal cord pathways of the same name, going through the visual tubercles of the diencephalon to the somatosensory cortex.

Through cochlear auditory nuclei and through vestibular nuclei ascending sensory pathways from the auditory and vestibular receptors. In the projection zone of the temporal cortex.

Thus, the medulla oblongata regulates the activity of many vital functions of the body. Therefore, the slightest damage to the medulla oblongata (trauma, edema, hemorrhage, tumors), as a rule, leads to death.

Pons

The bridge is a thick roller that borders the medulla oblongata and cerebellar peduncles. The ascending and descending paths of the medulla oblongata pass through the bridge without interruption. The vestibulocochlear nerve (VIII pair) exits at the junction of the pons and the medulla oblongata. The vestibulocochlear nerve is sensitive and transmits information from auditory and vestibular receptors in the inner ear. In addition, mixed nerves, nuclei of the trigeminal nerve (V pair), abducens nerve (VI pair), and facial nerve (VII pair) are located in the pons Varolii. These nerves innervate the muscles of the face, scalp, tongue, and lateral rectus muscles of the eye.

On the transverse section, the bridge consists of the ventral and dorsal parts - between them the border is a trapezoid body, the fibers of which are attributed to the auditory pathway. In the region of the trapezius body there is a medial parabranchial nucleus, which is associated with the dentate nucleus of the cerebellum. The pons proper nucleus connects the cerebellum with the cerebral cortex. In the dorsal part of the bridge lie the nuclei of the reticular formation and continue the ascending and descending paths of the medulla oblongata.

The bridge performs complex and diverse functions aimed at maintaining the posture and maintaining the balance of the body in space when changing the speed of movement.

Vestibular reflexes are very important, the reflex arcs of which pass through the bridge. They provide the tone of the neck muscles, excitation of the vegetative centers, respiration, heart rate, and activity of the gastrointestinal tract.

The nuclei of the trigeminal, glossopharyngeal, vagus, and pons are involved in grasping, chewing, and swallowing food.

Neurons of the pontine reticular formation play a special role in activating the cerebral cortex and limiting the sensory influx of nerve impulses during sleep (Fig. 22, 23)

Rice. 22. Medulla oblongata and pons.

A. Top view (from the dorsal side).

B. Side view.

B. View from below (from the ventral side).

1 - tongue, 2 - anterior cerebral sail, 3 - median eminence, 4 - superior fossa, 5 - superior cerebellar peduncle, 6 - middle cerebellar peduncle, 7 - facial tubercle, 8 - inferior cerebellar peduncle, 9 - auditory tubercle, 10 - brain stripes, 11 - tape of the fourth ventricle, 12 - triangle of the hypoglossal nerve, 13 - triangle of the vagus nerve, 14 - areapos-terma, 15 - obex, 16 - tubercle of the sphenoid nucleus, 17 - tubercle of the tender nucleus, 18 - lateral funiculus, 19 - posterior lateral sulcus, 19 a - anterior lateral sulcus, 20 - sphenoid funiculus, 21 - posterior intermediate sulcus, 22 - tender cord, 23 - posterior median sulcus, 23 a - bridge - base), 23 b - pyramid of the medulla oblongata, 23 c - olive, 23 g - cross of the pyramids, 24 - leg of the brain, 25 - lower tubercle, 25 a - handle of the lower tubercle, 256 - upper tubercle

1 - trapezoid body 2 - core of the superior olive 3 - dorsal contains nuclei of VIII, VII, VI, V pairs of cranial nerves 4 - medal part of the bridge 5 - ventral part of the bridge contains its own nuclei and bridge 7 - transverse nuclei of the bridge 8 - pyramidal pathways 9 - middle cerebellar peduncle.

Rice. 23. Scheme of the internal structure of the bridge on the frontal section

Cerebellum

The cerebellum is a region of the brain located behind the cerebral hemispheres above the medulla oblongata and the pons.

Anatomically, in the cerebellum, the middle part is distinguished - the worm, and two hemispheres. With the help of three pairs of legs (lower, middle and upper), the cerebellum is connected to the brain stem. The lower legs connect the cerebellum with the medulla oblongata and spinal cord, the middle ones with the bridge, and the upper ones with the middle and diencephalon (Fig. 24).

1 - vermis 2 - central lobule 3 - uvula of the vermis 4 - anterior cerebellar velum 5 - superior hemisphere 6 - anterior cerebellar peduncle 8 - peduncle of the tuft 9 - tuft 10 - superior semilunar lobule 11 - inferior lunate lobule 12 - inferior hemisphere 13 - digastric lobule 14 - cerebellar lobule 15 - cerebellar tonsil 16 - pyramid of the vermis 17 - wing of the central lobule 18 - nodule 19 - apex 20 - groove 21 - worm socket 22 - worm tubercle 23 - quadrangular lobule.

Rice. 24. Internal structure of the cerebellum

The cerebellum is built according to the nuclear type - the surface of the hemispheres is represented by gray matter, which makes up the new cortex. The bark forms convolutions, which are separated from each other by furrows. Under the cerebellar cortex there is a white matter, in the thickness of which the paired nuclei of the cerebellum are isolated (Fig. 25). These include the kernels of the tent, the spherical nucleus, the cork nucleus, the dentate nucleus. The nuclei of the tent are associated with the vestibular apparatus, the spherical and cork nuclei with the movement of the body, the dentate nucleus with the movement of the limbs.

1- anterior legs of the cerebellum; 2 - the core of the tent; 3 - dentate nucleus; 4 - cork-like nucleus; 5 - white substance; 6 - hemispheres of the cerebellum; 7 - worm; 8 globular nucleus

Rice. 25. Cerebellar nuclei

The cerebellar cortex is of the same type and consists of three layers: molecular, ganglionic and granular, in which there are 5 types of cells: Purkinje cells, basket cells, stellate cells, granular cells and Golgi cells (Fig. 26). In the surface, molecular layer, there are dendritic branches of Purkinje cells, which are one of the most complex neurons in the brain. The dendritic processes are abundantly covered with spines, indicating a large number of synapses. In addition to Purkinje cells, this layer contains many axons of parallel nerve fibers (T-shaped branching axons of granule cells). In the lower part of the molecular layer are the bodies of basket cells, the axons of which form synaptic contacts in the region of the axon mounds of Purkinje cells. There are also stellate cells in the molecular layer.

A. Purkinje cell. B. Grain cells.

B. Golgi cell.

Rice. 26. Types of cerebellar neurons.

Beneath the molecular layer is the ganglionic layer, which houses the Purkinje cell bodies.

The third layer - granular - is represented by the bodies of intercalary neurons (grain cells or granule cells). In the granular layer there are also Golgi cells, the axons of which rise into the molecular layer.

Only two types of afferent fibers enter the cerebellar cortex: climbing and mossy, through which nerve impulses arrive in the cerebellum. Each climbing fiber has contact with one Purkinje cell. The ramifications of the mossy fiber form contacts mainly with granular neurons, but do not contact with Purkinje cells. The synapses of the mossy fiber are excitatory (Fig. 27).

The cortex and nuclei of the cerebellum receive excitatory impulses through both climbing and bryophyte fibers. From the cerebellum, the signals come only from Purkinje cells (P), which inhibit the activity of neurons in the nuclei of the 1st cerebellum (I). The intrinsic neurons of the cerebellar cortex include excitatory granule cells (3) and inhibitory basket neurons (K), Golgi neurons (G) and stellate neurons (Sv). Arrows indicate the direction of movement of nerve impulses. There are both exciting (+) and; inhibitory (-) synapses.

Rice. 27. Neural circuit of the cerebellum.

Thus, two types of afferent fibers enter the cerebellar cortex: climbing and mossy. Information is transmitted through these fibers from tactile receptors and receptors of the musculoskeletal system, as well as from all brain structures that regulate the motor function of the body.

The efferent influence of the cerebellum is carried out through the axons of Purkinje cells, which are inhibitory. The axons of Purkinje cells exert their influence either directly on the motor neurons of the spinal cord, or indirectly through the neurons of the cerebellar nuclei or other motor centers.

In humans, due to upright posture and labor activity the cerebellum and its hemispheres reach greatest development and size.

With damage to the cerebellum, imbalance and muscle tone are observed. The nature of the damage depends on the location of the damage. So, when the nuclei of the tent are damaged, the balance of the body is disturbed. This is manifested in a staggering gait. If the worm, cork and spherical nuclei are damaged, the work of the muscles of the neck and torso is disrupted. The patient has difficulty eating. With damage to the hemispheres and the dentate nucleus - the work of the muscles of the limbs (tremor), its professional activity is hampered.

In addition, in all patients with damage to the cerebellum due to impaired coordination of movements and tremor (trembling), fatigue quickly occurs.

midbrain

The midbrain, like the medulla oblongata and the pons Varolii, belongs to the stem structures (Fig. 28).

1 - komisura leashes

2 - leash

3 - pineal gland

4 - superior colliculus of the midbrain

5 - medial geniculate body

6 - lateral geniculate body

7 - lower colliculus of the midbrain

8 - upper legs of the cerebellum

9 - middle legs of the cerebellum

10 - lower legs of the cerebellum

11- medulla oblongata

Rice. 28. Hind brain

The midbrain consists of two parts: the roof of the brain and the legs of the brain. The roof of the midbrain is represented by the quadrigemina, in which the upper and lower tubercles are distinguished. In the thickness of the legs of the brain, paired clusters of nuclei are distinguished, called the black substance and the red nucleus. Through the midbrain, ascending paths pass to the diencephalon and cerebellum and descending paths - from the cerebral cortex, subcortical nuclei and diencephalon to the nuclei of the medulla oblongata and spinal cord.

In the lower colliculus of the quadrigemina are neurons that receive afferent signals from auditory receptors. Therefore, the lower tubercles of the quadrigemina are called the primary auditory center. The reflex arc of the orienting auditory reflex passes through the primary auditory center, which manifests itself in turning the head towards the acoustic signal.

The superior tubercles of the quadrigemina are the primary visual center. The neurons of the primary visual center receive afferent impulses from photoreceptors. The superior tubercles of the quadrigemina provide an orienting visual reflex - turning the head in the direction of the visual stimulus.

In the implementation of the orienting reflexes, the nuclei of the lateral and oculomotor nerves take part, which innervate the muscles of the eyeball, ensuring its movement.

The red nucleus contains neurons of different sizes. From the large neurons of the red nucleus, the descending rubro-spinal tract begins, which has an effect on motor neurons and finely regulates muscle tone.

The neurons of the substantia nigra contain the pigment melanin and give this nucleus its dark color. The substantia nigra, in turn, sends signals to the neurons of the reticular nuclei of the brain stem and subcortical nuclei.

The substantia nigra is involved in complex coordination of movements. It contains dopaminergic neurons, i.e. releasing dopamine as a mediator. One part of these neurons regulates emotional behavior, while the other part plays an important role in the control of complex motor acts. Damage to the substantia nigra, leading to degeneration of dopaminergic fibers, causes the inability to start performing voluntary movements of the head and hands when the patient is sitting quietly (Parkinson's disease) (Fig. 29 A, B).

Rice. 29A. 1 - hillock 2 - cerebral aqueduct 3 - central gray matter 4 - substantia nigra 5 - medial sulcus of the cerebral peduncle

Rice. 29B. Scheme of the internal structure of the midbrain at the level of the inferior colliculi (frontal section)

1 - nucleus of the inferior colliculus, 2 - motor pathway of the extrapyramidal system, 3 - dorsal decussation of the tegmentum, 4 - red nucleus, 5 - red nuclear - spinal tract, 6 - ventral decussation of the tegmentum, 7 - medial loop, 8 - lateral loop, 9 - reticular formation, 10 - medial longitudinal bundle, 11 - nucleus of the mesencephalic tract of the trigeminal nerve, 12 - nucleus of the lateral nerve, I-V - descending motor pathways of the brain stem

Rice. 29. Scheme of the internal structure of the midbrain

diencephalon

The diencephalon forms the walls of the third ventricle. Its main structures are the visual tubercles (thalamus) and the hypothalamic region (hypothalamus), as well as the suprathalamic region (epithalamus) (Fig. 30 A, B).

Rice. 30 A. 1 - thalamus (visual tubercle) - the subcortical center of all types of sensitivity, the "sensory" of the brain; 2 - epithalamus (supratuberous region); 3 - metathalamus (foreign region).

Rice. 30 B. Diagrams of the visual brain ( thalamencephalon ): a - top view b - rear and bottom view.

Thalamus (thalamus) 1 - anterior burf of the thalamus, 2 - pillow 3 - intertubercular fusion 4 - brain strip of the thalamus

Epithalamus (supratuberous region) 5 - triangle of the leash, 6 - leash, 7 - commissure of the leash, 8 - pineal body (pineal gland)

Metathalamus (foreign region) 9 - lateral geniculate body, 10 - medial geniculate body, 11 - III ventricle, 12 - roof of the midbrain

Rice. 30. Visual Brain

In the depths of the brain tissue of the diencephalon are the nuclei of the external and internal geniculate bodies. The outer border is formed by white matter separating the diencephalon from the final.

Thalamus (optical tubercles)

The neurons of the thalamus form 40 nuclei. Topographically, the nuclei of the thalamus are divided into anterior, median and posterior. Functionally, these nuclei can be divided into two groups: specific and nonspecific.

Specific nuclei are part of specific pathways. These are ascending pathways that transmit information from the receptors of the sense organs to the projection zones of the cerebral cortex.

The most important of the specific nuclei are the lateral geniculate body, which is involved in the transmission of signals from photoreceptors, and the medial geniculate body, which transmits signals from auditory receptors.

Nonspecific thalamic ridges are referred to as the reticular formation. They play the role of integrative centers and have a predominantly activating ascending effect on the cortex of the cerebral hemispheres (Fig. 31 A, B)

1 - front group (olfactory); 2 - rear group (visual); 3 - lateral group (general sensitivity); 4 - medial group (extrapyramidal system; 5 - central group (reticular formation).

Rice. 31B. Frontal section of the brain at the level of the middle of the thalamus. 1a - anterior nucleus of the thalamus. 16 - medial nucleus of the thalamus, 1c - lateral nucleus of the thalamus, 2 - lateral ventricle, 3 - fornix, 4 - caudate nucleus, 5 - internal capsule, 6 - external capsule, 7 - external capsule (capsulaextrema), 8 - ventral nucleus visual mound, 9 - subthalamic nucleus, 10 - third ventricle, 11 - brain stem. 12 - bridge, 13 - interpeduncular fossa, 14 - hippocampal stalk, 15 - lower horn of the lateral ventricle. 16 - black substance, 17 - island. 18 - pale ball, 19 - shell, 20 - Trout H fields; and b. 21 - interthalamic fusion, 22 - corpus callosum, 23 - tail of the caudate nucleus.

Fig 31. Scheme of groups of nuclei of the thalamus

Activation of neurons of nonspecific nuclei of the thalamus is especially effectively caused by pain signals (thalamus is the highest center of pain sensitivity).

Damage to the nonspecific nuclei of the thalamus also leads to impaired consciousness: loss active communication organism with the environment.

hypothalamus (hypothalamus)

The hypothalamus is formed by a group of nuclei located at the base of the brain. The nuclei of the hypothalamus are the subcortical centers of the autonomic nervous system of all vital body functions.

Topographically, the hypothalamus is divided into the preoptic region, the regions of the anterior, middle and posterior hypothalamus. All nuclei of the hypothalamus are paired (Figure 32 A-D).

1 - plumbing 2 - red core 3 - tire 4 - black substance 5 - brain stem 6 - mastoid bodies 7 - anterior perforated substance 8 - olfactory triangle 9 - funnel 10 - optic chiasm 11. optic nerve 12 - gray tubercle 13 - posterior perforated substance 14 - lateral geniculate body 15 - medial geniculate body 16 - pillow 17 - optic tract

Rice. 32A. Metathalamus and hypothalamus

a - bottom view; b - median sagittal section.

Visual part (parsoptica): 1 - end plate; 2 - optic chiasm; 3 - visual tract; 4 - gray tubercle; 5 - funnel; 6 - pituitary gland;

Olfactory part: 7 - mammillary bodies - subcortical olfactory centers; 8 - the hypothalamic region in the narrow sense of the word is a continuation of the legs of the brain, contains a black substance, a red nucleus and a Lewis body, which is a link in the extrapyramidal system and a vegetative center; 9 - hypotuberous Monroe's furrow; 10 - Turkish saddle, in the fossa of which is the pituitary gland.

Rice. 32B. Hypodermic area (hypothalamus)

Rice. 32V. Major nuclei of the hypothalamus

1 - nucleus supraopticus; 2 - nucleuspreopticus; 3 - nuclius paraventricularis; 4 - nucleusinfundibularus; 5 - nucleuscorporismamillaris; 6 - optic chiasm; 7 - pituitary gland; 8 - gray tubercle; 9 - mastoid body; 10 bridge.

Rice. 32G. Diagram of the neurosecretory nuclei of the hypothalamic region (Hypothalamus)

The preoptic region includes the periventricular, medial, and lateral preoptic nuclei.

The anterior hypothalamus includes the supraoptic, suprachiasmatic, and paraventricular nuclei.

The middle hypothalamus makes up the ventromedial and dorsomedial nuclei.

In the posterior hypothalamus, the posterior hypothalamic, perifornical, and mamillary nuclei are distinguished.

The connections of the hypothalamus are extensive and complex. Afferent signals to the hypothalamus come from the cerebral cortex, subcortical nuclei and from the thalamus. The main efferent pathways reach the midbrain, thalamus and subcortical nuclei.

The hypothalamus is the highest center of regulation of the cardiovascular system, water-salt, protein, fat, carbohydrate metabolism. In this area of the brain are centers associated with the regulation of eating behavior. An important role of the hypothalamus is regulation. Electrical stimulation of the posterior nuclei of the hypothalamus leads to hyperthermia, as a result of an increase in metabolism.

The hypothalamus is also involved in maintaining the sleep-wake biorhythm.

The nuclei of the anterior hypothalamus are associated with the pituitary gland and transport biologically active substances produced by the neurons of these nuclei. The neurons of the preoptic nucleus produce releasing factors (statins and liberins) that control the synthesis and release of pituitary hormones.

The neurons of the preoptic, supraoptic, paraventricular nuclei produce true hormones - vasopressin and oxytocin, which descend along the axons of the neurons to the neurohypophysis, where they are stored until they are released into the blood.

Neurons of the anterior pituitary gland produce 4 types of hormones: 1) somatotropic hormone that regulates growth; 2) a gonadotropic hormone that promotes the growth of germ cells, the corpus luteum, enhances milk production; 3) thyroid-stimulating hormone - stimulates the function of the thyroid gland; 4) adrenocorticotropic hormone - enhances the synthesis of hormones of the adrenal cortex.

The intermediate lobe of the pituitary gland secretes the hormone intermedin, which affects skin pigmentation.

The posterior pituitary gland secretes two hormones - vasopressin, which affects the smooth muscles of arterioles, and oxytocin - acts on the smooth muscles of the uterus and stimulates the release of milk.

The hypothalamus also plays an important role in emotional and sexual behavior.

The pineal gland is part of the epithalamus (pineal gland). Pineal hormone - melatonin - inhibits the formation of gonadotropic hormones in the pituitary gland, and this in turn delays sexual development.

forebrain

The forebrain consists of three anatomically separate parts - the cerebral cortex, white matter and subcortical nuclei.

In accordance with the phylogeny of the cerebral cortex, the ancient cortex (archicortex), the old cortex (paleocortex) and the new cortex (neocortex) are distinguished. The ancient cortex includes olfactory bulbs, which receive afferent fibers from the olfactory epithelium, olfactory tracts - located on the lower surface of the frontal lobe and olfactory tubercles - secondary olfactory centers.

The old cortex includes the cingulate cortex, the hippocampal cortex, and the amygdala.

All other areas of the cortex are new cortex. The ancient and old cortex is called the olfactory brain (Fig. 33).

The olfactory brain, in addition to the functions associated with smell, provides reactions of alertness and attention, takes part in the regulation of the autonomic functions of the body. This system also plays an important role in the implementation of instinctive forms of behavior (food, sexual, defensive) and the formation of emotions.

a - bottom view; b - on the sagittal section of the brain

Peripheral department: 1 - bulbusolfactorius (olfactory bulb; 2 - tractusolfactories (olfactory pathway); 3 - trigonumolfactorium (olfactory triangle); 4 - substantiaperforateanterior (anterior perforated substance).

The central section is the gyrus of the brain: 5 - vaulted gyrus; 6 - hippocampus is located in the cavity of the lower horn of the lateral ventricle; 7 - continuation of the gray vestment of the corpus callosum; 8 - vault; 9 - transparent septum conducting paths of the olfactory brain.

Figure 33. Olfactory brain

Irritation of the structures of the old cortex affects the cardiovascular system and respiration, causes hypersexuality, and changes emotional behavior.

With electrical stimulation of the tonsils, effects associated with the activity of the digestive tract are observed: licking, chewing, swallowing, changes in intestinal motility. Irritation of the tonsil also affects the activity of internal organs - the kidneys, bladder, uterus.

Thus, there is a connection between the structures of the old cortex and the autonomic nervous system, with processes aimed at maintaining the homeostasis of the internal environment of the body.

telencephalon

The structure of the telencephalon includes: the cerebral cortex, white matter and subcortical nuclei located in its thickness.

The surface of the cerebral hemispheres is folded. Furrows - depressions divide it into shares.

The central (Roland) sulcus separates the frontal lobe from the parietal lobe. The lateral (Sylviian) sulcus separates the temporal lobe from the parietal and frontal lobes. The occipital-parietal sulcus forms the border between the parietal, occipital and temporal lobes (Fig. 34 A, B, Fig. 35)

1 - superior frontal gyrus; 2 - middle frontal gyrus; 3 - precentral gyrus; 4 - postcentral gyrus; 5 - lower parietal gyrus; 6 - superior parietal gyrus; 7 - occipital gyrus; 8 - occipital groove; 9 - intraparietal groove; 10 - central furrow; 11 - precentral gyrus; 12 - lower frontal groove; 13 - upper frontal groove; 14 - vertical slot.

Rice. 34A. The brain from the dorsal surface

1 - olfactory groove; 2 - anterior perforated substance; 3 - hook; 4 - middle temporal sulcus; 5 - lower temporal sulcus; 6 - furrow of a seahorse; 7 - circumferential furrow; 8 - spur furrow; 9 - wedge; 10 - parahippocampal gyrus; 11 - occipital-temporal groove; 12 - lower parietal gyrus; 13 - olfactory triangle; 14 - direct gyrus; 15 - olfactory tract; 16 - olfactory bulb; 17 - vertical slot.

Rice. 34B. The brain from the ventral surface

1 - central furrow (Roland); 2 - lateral furrow (Sylvian furrow); 3 - precentral furrow; 4 - upper frontal groove; 5 - lower frontal furrow; 6 - ascending branch; 7 - front branch; 8 - transcentral furrow; 9 - intraparietal groove; 10- superior temporal sulcus; 11 - lower temporal sulcus; 12 - transverse occipital sulcus; 13 - occipital sulcus.

Rice. 35. Furrows of the upper lateral surface of the hemisphere (left side)

Thus, the furrows divide the hemispheres of the telencephalon into five lobes: the frontal, parietal, temporal, occipital and insular lobes, which are located under the temporal lobes (Fig. 36).

Rice. 36. Projection (marked with dots) and associative (light) areas of the cerebral cortex. The projection areas include the motor area (frontal lobe), the somatosensory area (parietal lobe), the visual area (occipital lobe), and the auditory area (temporal lobe).

Furrows are also located on the surface of each lobe.

There are three orders of furrows: primary, secondary and tertiary. The primary furrows are relatively stable and the deepest. These are the boundaries of large morphological parts of the brain. The secondary furrows depart from the primary, and the tertiary from the secondary.

Between the furrows there are folds - convolutions, the shape of which is determined by the configuration of the furrows.

In the frontal lobe, the superior, middle, and inferior frontal gyri are distinguished. The temporal lobe contains the superior, middle, and inferior temporal gyri. The anterior central gyrus (precentral) is located in front of the central sulcus. The posterior central gyrus (postcentral) lies behind the central sulcus.

In humans, there is a large variability of the furrows and convolutions of the telencephalon. Despite this individual variability in the external structure of the hemispheres, this does not affect the structure of personality and consciousness.

Cytoarchitectonics and myeloarchitectonics of the neocortex

In accordance with the division of the hemispheres into five lobes, five main areas are distinguished - frontal, parietal, temporal, occipital and insular, which have differences in structure and perform different functions. However, the general plan of the structure of the new crust is the same. New bark- this is a layered structure (Fig. 37). I - molecular layer, formed mainly by nerve fibers running parallel to the surface. A small number of granular cells are located among the parallel fibers. Under the molecular layer is layer II - the outer granular one. Layer III - external pyramidal, IV layer, internal granular, V layer - internal pyramidal and VI layer - multiform. The names of the layers are given by the name of the neurons. Accordingly, in layers II and IV, the soma of neurons have a rounded shape (grain cells) (outer and inner granular layers), and in layers III and IV, the somas have a pyramidal shape (in the outer pyramidal - small pyramids, and in the inner pyramid - large pyramids or Betz cells). Layer VI is characterized by the presence of neurons various forms(fusiform, triangular, etc.).

The main afferent inputs to the cerebral cortex are nerve fibers coming from the thalamus. Cortical neurons that perceive afferent impulses going through these fibers are called sensory, and the area where sensory neurons are located is called projection cortical zones.

The main efferent outputs from the cortex are the axons of the layer V pyramids. These are efferent, motor neurons involved in the regulation of motor functions. Most cortical neurons are intercalary, involved in information processing and providing intercortical connections.

Typical cortical neurons

Roman numerals denote cell layers. I - molecular structure; II - outer granular layer; III - outer pyramidal layer; IV - inner granular layer; V - inner amide layer; VI-multiform layer.

a - afferent fibers; b - cell types detected on preparations impregnated by the Goldbzhi method; c - cytoarchitectonics revealed by Nissl staining. 1 - horizontal cells, 2 - Kes's strip, 3 - pyramidal cells, 4 - stellate cells, 5 - external Bellarge's strip, 6 - internal Bellarge's strip, 7 - modified pyramidal cell.

Rice. 37. Cytoarchitectonics (A) and myeloarchitectonics (B) of the cerebral cortex.

While maintaining the general plan of the structure, it was found that different parts of the bark (within the same area) differ in the thickness of the layers. In some layers, several sublayers can be distinguished. In addition, there are differences in cellular composition (diversity of neurons, density and their location). Taking into account all these differences, Brodman identified 52 areas, which he called cytoarchitectonic fields and designated with Arabic numerals from 1 to 52 (Fig. 38 A, B).

A side view. B mid-sagittal; cut.

Rice. 38. The layout of the fields according to Boardman

Each cytoarchitectonic field differs not only cellular structure, but also by the location of nerve fibers, which can go both in vertical and horizontal directions. The accumulation of nerve fibers within the cytoarchitectonic field is called myeloarchitectonics.

At present, the "columnar principle" of the organization of the projection zones of the cortex is gaining more and more recognition.

According to this principle, each projection zone consists of a large number vertically oriented columns, approximately 1 mm in diameter. Each column unites about 100 neurons, among which there are sensory, intercalary and efferent neurons interconnected by synaptic connections. A single “cortical column” is involved in the processing of information from a limited number of receptors, i.e. performs a specific function.

Hemispheric fiber system

Both hemispheres have three types of fibers. Through projection fibers, excitation enters the cortex from receptors along specific pathways. Associative fibers connect different areas of the same hemisphere. For example, the occipital region with the temporal region, the occipital region with the frontal region, the frontal region with the parietal region. Commissural fibers connect symmetrical regions of both hemispheres. Among the commissural fibers, there are: anterior, posterior cerebral commissures and the corpus callosum (Fig. 39 A.B).

Rice. 39A. a - medial surface of the hemisphere;

b - upper lateral surface of the hemisphere;

A - frontal pole;

B - occipital pole;

C - corpus callosum;

1 - arcuate fibers of the cerebrum connect adjacent gyri;

2 - belt - a bundle of the olfactory brain lies under the vaulted gyrus, extends from the region of the olfactory triangle to the hook;

3 - the lower longitudinal bundle connects the occipital and temporal region;

4 - the upper longitudinal bundle connects the frontal, occipital, temporal lobe and lower parietal lobule;

5 - a hook-shaped bundle is located at the anterior edge of the island and connects the frontal pole with the temporal.

Rice. 39B. The cerebral cortex in cross section. Both hemispheres are connected by bundles of white matter, forming the corpus callosum (commissural fibers).

Rice. 39. Scheme of associative fibers

Reticular formation

The reticular formation (the reticulum of the brain) was described by anatomists at the end of the last century.

The reticular formation begins in the spinal cord, where it is represented by the gelatinous substance of the base of the hindbrain. Its main part is located in the central brain stem and in the diencephalon. It consists of neurons of various shapes and sizes, which have extensive branching processes going in different directions. Among the processes, short and long nerve fibers are distinguished. Short processes provide local connections, long processes form ascending and descending paths of the reticular formation.

Accumulations of neurons form nuclei that are located at different levels of the brain (spinal, oblong, middle, intermediate). Most of the nuclei of the reticular formation do not have clear morphological boundaries and the neurons of these nuclei are combined only according to a functional feature (respiratory, cardiovascular center, etc.). However, at the level of the medulla oblongata, nuclei with clearly defined boundaries are isolated - reticular giant cell, reticular small cell and lateral nuclei. The nuclei of the reticular formation of the bridge are essentially a continuation of the nuclei of the reticular formation of the medulla oblongata. The largest of them are the caudal, medial and oral nuclei. The latter passes into the cellular group of nuclei of the reticular formation of the midbrain and the reticular nucleus of the tegmentum. The cells of the reticular formation are the beginning of both ascending and descending pathways, giving numerous collaterals (endings) that form synapses on neurons of different nuclei of the central nervous system.

Fibers of reticular cells traveling to the spinal cord form the reticulospinal tract. The fibers of the ascending tracts, starting in the spinal cord, connect the reticular formation with the cerebellum, midbrain, diencephalon, and cerebral cortex.

Allocate specific and non-specific reticular formation. For example, some of the ascending pathways of the reticular formation receive collaterals from specific pathways (visual, auditory, etc.) through which afferent impulses are transmitted to the projection zones of the cortex.

Nonspecific ascending and descending pathways of the reticular formation affect the excitability of various parts of the brain, primarily the cerebral cortex and the spinal cord. These influences according to their functional value can be both activating and inhibitory, therefore, they distinguish: 1) ascending activating influence, 2) ascending inhibitory influence, 3) descending activating influence, 4) descending inhibitory influence. Based on these factors, the reticular formation is considered as a non-specific regulatory system of the brain.

The most studied activating effect of the reticular formation on the cerebral cortex. Most of the ascending fibers of the reticular formation diffusely terminate in the cortex of the hemispheres and maintain its tone and provide attention. An example of inhibitory descending influences of the reticular formation is a decrease in the tone of human skeletal muscles during certain stages of sleep.

Neurons of the reticular formation are extremely sensitive to humoral substances. This is an indirect mechanism of the influence of various humoral factors and the endocrine system on the higher parts of the brain. Consequently, the tonic effects of the reticular formation depend on the state of the whole organism (Fig. 40).

Rice. 40. The activating reticular system (ARS) is a nervous network through which sensory excitation is transmitted from the reticular formation of the brain stem to the nonspecific nuclei of the thalamus. Fibers from these nuclei regulate the activity level of the cortex.

Subcortical nuclei

The subcortical nuclei are part of the telencephalon and are located inside the white matter of the cerebral hemispheres. These include the caudate body and the shell, united under the general name "striated body" (striatum) and the pale ball, consisting of the lenticular body, husk and tonsil. The subcortical nuclei and nuclei of the midbrain (red nucleus and black substance) make up the system of basal ganglia (nuclei) (Fig. 41). The basal ganglia receive impulses from the motor cortex and cerebellum. In turn, signals from the basal ganglia are sent to the motor cortex, cerebellum and reticular formation, i.e. there are two neural loops: one connects the basal ganglia with the motor cortex, the other with the cerebellum.

Rice. 41. Basal ganglia system

Subcortical nuclei are involved in the regulation motor activity, regulating complex movements when walking, maintaining a posture, while eating. They organize slow movements (stepping over obstacles, threading a needle, etc.).

There is evidence that the striatum is involved in the processes of memorizing motor programs, since irritation of this structure leads to impaired learning and memory. The striatum has an inhibitory effect on various manifestations of motor activity and on the emotional components of motor behavior, in particular, on aggressive reactions.

The main mediators of the basal ganglia are: dopamine (especially in the substantia nigra) and acetylcholine. The defeat of the basal ganglia causes slow writhing involuntary movements, against which sharp muscle contractions occur. Involuntary jerky movements of the head and limbs. Parkinson's disease, the main symptoms of which are tremor (trembling) and muscle rigidity (a sharp increase in the tone of the extensor muscles). Due to rigidity, the patient can hardly start moving. Constant tremor interferes with small movements. Parkinson's disease occurs when the substantia nigra is damaged. Normally, the substantia nigra has an inhibitory effect on the caudate nucleus, putamen, and globus pallidus. When it is destroyed, the inhibitory influences are eliminated, as a result of which the excitatory basal ganglia increase on the cerebral cortex and reticular formation, which causes the characteristic symptoms of the disease.

limbic system

The limbic system is represented by the divisions of the new cortex (neocortex) and the diencephalon located on the border. It combines complexes of structures of different phylogenetic age, some of which are cortical, and some are nuclear.

The cortical structures of the limbic system include the hippocampal, parahippocampal, and cingulate gyrus (old cortex). The ancient cortex is represented by the olfactory bulb and olfactory tubercles. The neocortex is part of the frontal, insular, and temporal cortices.

The nuclear structures of the limbic system combine the amygdala and septal nuclei and the anterior thalamic nuclei. Many anatomists classify the preoptic region of the hypothalamus and the mammillary bodies as part of the limbic system. The structures of the limbic system form 2-way connections and are connected with other parts of the brain.

The limbic system controls emotional behavior and regulates the endogenous factors that provide motivation. Positive emotions are associated predominantly with excitation of adrenergic neurons, while negative emotions, as well as fear and anxiety, are associated with a lack of excitation of noradrenergic neurons.

The limbic system is involved in the organization of orienting-exploratory behavior. Thus, “novelty” neurons were found in the hippocampus, which change their impulse activity when new stimuli appear. The hippocampus plays an essential role in maintaining the internal environment of the body, is involved in the processes of learning and memory.

Consequently, the limbic system organizes the processes of self-regulation of behavior, emotions, motivation and memory (Fig. 42).

Rice. 42. Limbic system

autonomic nervous system

The autonomic (vegetative) nervous system provides regulation of internal organs, strengthening or weakening their activity, performs an adaptive-trophic function, regulates the level of metabolism (metabolism) in organs and tissues (Fig. 43, 44).

1 - sympathetic trunk; 2 - cervicothoracic (star-shaped) node; 3 - middle cervical node; 4 - upper cervical knot; 5 - internal carotid artery; 6 - celiac plexus; 7 - superior mesenteric plexus; 8 - inferior mesenteric plexus

Rice. 43. Sympathetic part of the autonomic nervous system,

III - oculomotor nerve; YII - facial nerve; IX - glossopharyngeal nerve; X - vagus nerve.

1 - ciliary knot; 2 - pterygopalatine node; 3 - ear knot; 4 - submandibular node; 5 - sublingual node; 6 - parasympathetic sacral nucleus; 7 - extramural pelvic node.

Rice. 44. Parasympathetic part of the autonomic nervous system.

The autonomic nervous system includes parts of both the central and peripheral nervous systems. Unlike the somatic, in the autonomic nervous system, the efferent part consists of two neurons: preganglionic and postganglionic. Preganglionic neurons are located in the central nervous system. Postganglionic neurons are involved in the formation of autonomic ganglia.

The autonomic nervous system is divided into sympathetic and parasympathetic divisions.

In the sympathetic division, preganglionic neurons are located in the lateral horns of the spinal cord. The axons of these cells (preganglionic fibers) approach the sympathetic ganglia of the nervous system, located on both sides of the spine in the form of a sympathetic nerve chain.

Postganglionic neurons are located in the sympathetic ganglia. Their axons exit as part of the spinal nerves and form synapses on the smooth muscles of the internal organs, glands, vessel walls, skin and other organs.

In the parasympathetic nervous system, preganglionic neurons are located in the nuclei of the brainstem. Axons of preganglionic neurons are part of the oculomotor, facial, glossopharyngeal and vagus nerves. In addition, preganglionic neurons are also found in the sacral spinal cord. Their axons go to the rectum, bladder, to the walls of blood vessels that supply blood to the organs located in the pelvic area. Preganglionic fibers form synapses on postganglionic neurons of parasympathetic ganglia located near the effector or inside it (in the latter case, the parasympathetic ganglion is called intramural).

All parts of the autonomic nervous system are subordinate to the higher parts of the central nervous system.

Functional antagonism of the sympathetic and parasympathetic nervous systems was noted, which is of great adaptive importance (see Table 1).

SECTION I V . DEVELOPMENT OF THE NERVOUS SYSTEM

The nervous system begins to develop at the 3rd week of intrauterine development from the ectoderm (outer germ layer).

The ectoderm thickens on the dorsal (dorsal) side of the embryo. This forms the neural plate. Then the neural plate bends deep into the embryo and a neural groove is formed. The edges of the neural groove close to form the neural tube. A long hollow neural tube, lying first on the surface of the ectoderm, separates from it and plunges inward, under the ectoderm. The neural tube expands at the anterior end, from which the brain is later formed. The rest of the neural tube is transformed into the brain (Fig. 45).

Rice. 45. Stages of embryogenesis of the nervous system in a transverse schematic section, a - medullary plate; b and c - medullary groove; d and e - brain tube. 1 - horny leaf (epidermis); 2 - ganglion roller.

From the cells migrating from the side walls of the neural tube, two neural crests are laid - nerve cords. Subsequently, spinal and autonomic ganglia and Schwann cells are formed from the nerve cords, which form the myelin sheaths of nerve fibers. In addition, neural crest cells are involved in the formation of the pia mater and arachnoid. In the inner word of the neural tube, increased cell division occurs. These cells differentiate into 2 types: neuroblasts (progenitors of neurons) and spongioblasts (progenitors of glial cells). Simultaneously with cell division, the head end of the neural tube is divided into three sections - the primary cerebral vesicles. Accordingly, they are called the anterior (I bladder), middle (II bladder) and posterior (III bladder) brain. In subsequent development, the brain is divided into the terminal (large hemispheres) and diencephalon. The midbrain is preserved as a whole, and the hindbrain is divided into two sections, including the cerebellum with the bridge and the medulla oblongata. This is the 5-bladder stage of brain development (Fig. 46,47).

a - five brain pathways: 1 - first bubble (telencephalon); 2 - the second bubble (the diencephalon); 3 - third bubble (midbrain); 4- fourth bubble (medulla oblongata); between the third and fourth bubble - isthmus; b - development of the brain (according to R. Sinelnikov).

Rice. 46. Development of the brain (diagram)

A - formation of primary blisters (up to the 4th week embryonic development). B - F - formation of secondary bubbles. B, C - the end of the 4th week; G - the sixth week; D - 8-9th weeks, ending with the formation of the main parts of the brain (E) - by the 14th week.

3a - isthmus of the rhomboid brain; 7 end plate.

Stage A: 1, 2, 3 - primary cerebral vesicles

1 - forebrain,

2 - midbrain,

3 - hindbrain.

Stage B: the forebrain is divided into hemispheres and basal ganglia (5) and diencephalon (6)

Stage B: The rhomboid brain (3a) is subdivided into the hindbrain, including the cerebellum (8), the pons (9) stage E, and the medulla oblongata (10) stage E

Stage E: the spinal cord is formed (4)

Rice. 47. Developing brain.

The formation of nerve bubbles is accompanied by the appearance of bends due to different rates of maturation of parts of the neural tube. By the 4th week of intrauterine development, the parietal and occipital flexures are formed, and during the 5th week, the pontine flexure is formed. By the time of birth, only the curvature of the brain stem is preserved almost at a right angle in the region of the junction of the midbrain and diencephalon (Fig. 48).

Lateral view illustrating the flexures in the midbrain (A), cervical (B) regions of the brain, as well as in the region of the bridge (C).

1 - eye bubble, 2 - forebrain, 3 - midbrain; 4 - hindbrain; 5 - auditory vesicle; 6 - spinal cord; 7 - diencephalon; 8 - telencephalon; 9 - rhombic lip. Roman numerals indicate the origin of the cranial nerves.

Rice. 48. Developing brain (from the 3rd to the 7th week of development).

At the beginning, the surface of the cerebral hemispheres is smooth. First, at 11-12 weeks of intrauterine development, the lateral sulcus (Sylvius) is laid, then the central (Rolland's) sulcus. Quite quickly, furrows are formed within the lobes of the hemispheres, due to the formation of furrows and convolutions, the area of the cortex increases (Fig. 49).

Rice. 49. Side view of the developing hemispheres of the brain.

A- 11th week. B- 16_ 17 weeks. B- 24-26 weeks. G- 32-34 weeks. D is a newborn. The formation of a lateral fissure (5), a central sulcus (7) and other furrows and convolutions is shown.

I - telencephalon; 2 - midbrain; 3 - cerebellum; 4 - medulla oblongata; 7 - central furrow; 8 - bridge; 9 - furrows of the parietal region; 10 - furrows of the occipital region;

II - furrows of the frontal region.

By migration, neuroblasts form clusters - the nuclei that form the gray matter of the spinal cord, and in the brain stem - some nuclei of the cranial nerves.

Soma neuroblasts have a rounded shape. The development of a neuron is manifested in the appearance, growth and branching of processes (Fig. 50). A small short protrusion is formed on the neuron membrane at the site of the future axon - a growth cone. The axon is extended and nutrients are delivered to the growth cone along it. At the beginning of development, a neuron develops more processes compared to the finite number of processes of a mature neuron. Part of the processes is drawn into the soma of the neuron, and the remaining ones grow towards other neurons, with which they form synapses.

Rice. 50. Development of the spindle cell in human ontogenesis. The last two sketches show the difference in the structure of these cells in a child at the age of two years and an adult.

In the spinal cord, axons are short and form intersegmental connections. Longer projection fibers are formed later. A little later than the axon, the growth of dendrites begins. All branches of each dendrite are formed from one trunk. The number of branches and the length of the dendrites does not end in the prenatal period.

The increase in brain mass in the prenatal period occurs mainly due to an increase in the number of neurons and the number of glial cells.

The development of the cortex is associated with the formation of cell layers (in the cortex of the cerebellum - three layers, and in the cortex of the cerebral hemispheres - six layers).

The so-called glial cells play an important role in the formation of the cortical layers. These cells take a radial position and form two vertically oriented long processes. Migration of neurons occurs along the processes of these radial glial cells. First, more superficial layers of the crust are formed. Glial cells also take part in the formation of the myelin sheath. Sometimes one glial cell is involved in the formation of the myelin sheaths of several axons.

Table 2 reflects the main stages in the development of the nervous system of the embryo and fetus.

Table 2.

The main stages of development of the nervous system in the prenatal period.

*Age of fetus (weeks)*	*Development of the nervous system*
2,5	There is a neural groove
3.5	Formation of the neural tube and nerve cords
4	3 brain bubbles are formed; nerves and ganglia are formed
5	5 brain bubbles form
6	The meninges are outlined
7	Hemispheres of the brain reach a large size
8	Typical neurons appear in the cortex
10	The internal structure of the spinal cord is formed
12	Common structural features of the brain are formed; neuroglial cell differentiation begins
16	Distinguishable lobes of the brain
20-40	Myelination of the spinal cord begins (20 weeks), layers of the cortex appear (25 weeks), furrows and convolutions form (28-30 weeks), myelination of the brain begins (36-40 weeks)

Thus, the development of the brain in the prenatal period occurs continuously and in parallel, but is characterized by heterochrony: the rate of growth and development of phylogenetically older formations is greater than that of phylogenetically younger formations.

The leading role in the growth and development of the nervous system in the prenatal period is played by genetic factors. The average brain weight of a newborn is approximately 350 g.

Morpho-functional maturation of the nervous system continues in the postnatal period. By the end of the first year of life, the weight of the brain reaches 1000 g, while in an adult the weight of the brain is on average 1400 g. Consequently, the main increase in brain mass occurs in the first year of a child's life.

The increase in brain mass in the postnatal period occurs mainly due to an increase in the number of glial cells. The number of neurons does not increase, as they lose the ability to divide already in the prenatal period. The total density of neurons (the number of cells per unit volume) decreases due to the growth of the soma and processes. The number of branches increases in dendrites.

In the postnatal period, myelination of nerve fibers also continues both in the central nervous system and the nerve fibers that make up the peripheral nerves (cranial and spinal.).

The growth of the spinal nerves is associated with the development of the musculoskeletal system and the formation of neuromuscular synapses, and the growth of the cranial nerves with the maturation of the sense organs.

Thus, if in the prenatal period the development of the nervous system occurs under the control of the genotype and practically does not depend on the influence of the external environment, then in the postnatal period, external stimuli become increasingly important. Irritation of receptors causes afferent streams of impulses that stimulate the morpho-functional maturation of the brain.

Under the influence of afferent impulses, spines are formed on the dendrites of cortical neurons - outgrowths, which are special postsynaptic membranes. The more spines, the more synapses and the more involved the neuron is in information processing.

Throughout the entire postnatal ontogenesis up to the pubertal period, as well as in the prenatal period, the development of the brain occurs heterochronously. So, the final maturation of the spinal cord occurs earlier than the brain. The development of stem and subcortical structures, earlier than cortical ones, the growth and development of excitatory neurons overtakes the growth and development of inhibitory neurons. These are general biological patterns of growth and development of the nervous system.

Morphological maturation of the nervous system correlates with the features of its functioning at each stage of ontogenesis. Thus, earlier differentiation of excitatory neurons compared to inhibitory neurons ensures the predominance of flexor muscle tone over extensor tone. The arms and legs of the fetus are in a bent position - this causes a posture that provides minimal volume, so that the fetus takes up less space in the uterus.

Improving the coordination of movements associated with the formation of nerve fibers occurs throughout the entire preschool and school periods, which is manifested in the consistent mastering of the posture of sitting, standing, walking, writing, etc.

An increase in the speed of movements is mainly due to the processes of myelination of peripheral nerve fibers and an increase in the speed of conduction of excitation of nerve impulses.

The earlier maturation of subcortical structures compared to cortical ones, many of which are part of the limbic structure, determine the features emotional development children (great intensity of emotions, inability to restrain them is associated with the immaturity of the cortex and its weak inhibitory effect).

In the elderly and senile age, anatomical and histological changes in the brain occur. Often there is atrophy of the cortex of the frontal and upper parietal lobes. The furrows become wider, the ventricles of the brain increase, the volume of white matter decreases. There is a thickening of the meninges.

With age, neurons decrease in size, while the number of nuclei in cells may increase. In neurons, the content of RNA, which is necessary for the synthesis of proteins and enzymes, also decreases. This impairs the trophic functions of neurons. It is suggested that such neurons tire faster.

In old age, the blood supply to the brain is also disturbed, the walls of blood vessels thicken and cholesterol plaques (atherosclerosis) are deposited on them. It also impairs the activity of the nervous system.

LITERATURE

Atlas “Human Nervous System”. Comp. V.M. Astashev. M., 1997.

Blum F., Leyzerson A., Hofstadter L. Brain, mind and behavior. M.: Mir, 1988.

Borzyak E.I., Bocharov V.Ya., Sapina M.R. Human anatomy. - M.: Medicine, 1993. V.2. 2nd ed., revised. and additional

Zagorskaya V.N., Popova N.P. Anatomy of the nervous system. Course program. MOSU, M., 1995.

Kishsh-Sentagothai. Anatomical atlas of the human body. - Budapest, 1972. 45th ed. T. 3.

Kurepina M.M., Vokken G.G. Human anatomy. - M.: Enlightenment, 1997. Atlas. 2nd edition.

Krylova N.V., Iskrenko I.A. Brain and pathways (Human anatomy in diagrams and drawings). M.: Publishing House of the Peoples' Friendship University of Russia, 1998.

Brain. Per. from English. Ed. Simonova P.V. - M.: Mir, 1982.

Human morphology. Ed. B.A. Nikityuk, V.P. Chtetsov. - M.: Publishing House of Moscow State University, 1990. S. 252-290.

Prives M.G., Lysenkov N.K., Bushkovich V.I. Human anatomy. - L .: Medicine, 1968. S. 573-731.

Saveliev S.V. Stereoscopic atlas of the human brain. M., 1996.

Sapin M.R., Bilich G.L. Human anatomy. - M.: Higher school, 1989.

Sinelnikov R.D. Atlas of human anatomy. - M.: Medicine, 1996. 6th ed. T. 4.

Sade J., Ford D. Fundamentals of neurology. - M.: Mir, 1982.

Tissue is a collection of cells and intercellular substance similar in structure, origin and functions.

Some anatomists do not include the medulla oblongata in the hindbrain, but distinguish it as an independent department.

Subject. Structure and functions of the human nervous system

1 What is the nervous system

2 Central nervous system

Brain

Spinal cord

CNS

3 Autonomic nervous system

4 Development of the nervous system in ontogeny. Characteristics of the three-bubble and five-bubble stages of brain formation

What is the nervous system

Nervous system is a system that regulates the activity of all human organs and systems. This system causes:

1) the functional unity of all human organs and systems;

2) the connection of the whole organism with the environment.

Nervous system controls the activity of various organs, systems and apparatuses that make up the body. It regulates the functions of movement, digestion, respiration, blood supply, metabolic processes, etc. The nervous system establishes the relationship of the body with the external environment, unites all parts of the body into a single whole.

The nervous system according to the topographic principle is divided into central and peripheral ( rice. 1).

central nervous system(CNS) includes the brain and spinal cord.

TO peripheral part of the nervoussystems include spinal and cranial nerves with their roots and branches, nerve plexuses, nerve nodes, nerve endings.

In addition, the nervous system containstwo special parts : somatic (animal) and vegetative (autonomous).

somatic nervous system innervates mainly the organs of the soma (body): striated (skeletal) muscles (face, trunk, limbs), skin and some internal organs (tongue, larynx, pharynx). The somatic nervous system primarily performs the functions of connecting the body with the external environment, providing sensitivity and movement, causing contraction of the skeletal muscles. Since the functions of movement and feeling are characteristic of animals and distinguish them from plants, this part of the nervous system is calledanimal(animal). The actions of the somatic nervous system are controlled by human consciousness.

autonomic nervous system innervates the viscera, glands, smooth muscles of organs and skin, blood vessels and the heart, regulates metabolic processes in tissues. The autonomic nervous system influences the processes of the so-called plant life, common to animals and plants(metabolism, respiration, excretion, etc.), which is why its name comes from ( vegetative- vegetable).

Both systems are closely related, but the autonomic nervous system has some degree of autonomy and does not depend on our will, as a result of which it is also called autonomic nervous system.

She is being divided into two parts sympathetic And parasympathetic. The allocation of these departments is based both on the anatomical principle (differences in the location of the centers and the structure of the peripheral part of the sympathetic and parasympathetic nervous system), and on functional differences.

Excitation of the sympathetic nervous system contributes to the intensive activity of the body; excitation of the parasympathetic On the contrary, it helps to restore the resources expended by the body.

The sympathetic and parasympathetic systems have opposite influence on many organs, being functional antagonists. Yes, under influence of impulses coming along the sympathetic nerves, heart contractions become more frequent and intensified, blood pressure in the arteries rises, glycogen in the liver and muscles breaks down, blood glucose increases, pupils dilate, sensitivity of the sense organs and the efficiency of the central nervous system increase, bronchi narrow, contractions of the stomach and intestines are inhibited, secretion decreases gastric juice and pancreatic juice, the bladder relaxes and its emptying is delayed. Under the influence of impulses coming through the parasympathetic nerves, heart contractions slow down and weaken, blood pressure decreases, blood glucose decreases, contractions of the stomach and intestines are stimulated, secretion of gastric juice and pancreatic juice increases, etc.

central nervous system

Central nervous system (CNS)- the main part of the nervous system of animals and humans, consisting of a cluster of nerve cells (neurons) and their processes.

central nervous system consists of the brain and spinal cord and their protective membranes.

The outermost is dura mater , below it is located arachnoid (arachnoid ), and then pia mater fused to the surface of the brain. Between the soft and arachnoid membranes is subarachnoid (subarachnoid) space , containing cerebrospinal (cerebrospinal) fluid, in which both the brain and spinal cord literally float. The action of the buoyancy force of the fluid leads to the fact that, for example, the adult brain, which has an average weight of 1500 g, actually weighs 50–100 g inside the skull. The meninges and cerebrospinal fluid also play the role of shock absorbers, softening all kinds of shocks and shocks that experiences the body and which could cause damage to the nervous system.

CNS formed from gray and white matter .

Gray matter make up cell bodies, dendrites and unmyelinated axons, organized into complexes that include countless synapses and serve as information processing centers for many of the functions of the nervous system.

white matter consists of myelinated and unmyelinated axons that act as conductors that transmit impulses from one center to another. The gray and white matter also contain glial cells.

CNS neurons form many circuits that perform two main functions: provide reflex activity, as well as complex information processing in higher brain centers. These higher centers, such as the visual cortex (visual cortex), receive incoming information, process it, and transmit a response signal along the axons.

The result of the activity of the nervous system- this or that activity, which is based on the contraction or relaxation of muscles or the secretion or cessation of secretion of glands. It is with the work of muscles and glands that any way of our self-expression is connected. Incoming sensory information is processed by passing through a sequence of centers connected by long axons, which form specific pathways, such as pain, visual, auditory. sensitive (ascending) pathways go in an upward direction to the centers of the brain. Motor (descending)) paths connect the brain with the motor neurons of the cranial and spinal nerves. Pathways are usually organized in such a way that information (for example, pain or tactile) from the right side of the body goes to the left side of the brain and vice versa. This rule also applies to descending motor pathways: the right half of the brain controls the movements of the left half of the body, and the left half controls the right. From this general rule however, there are a few exceptions.

Brain

consists of three main structures: the cerebral hemispheres, the cerebellum and the trunk.

Large hemispheres - the largest part of the brain - contain higher nerve centers that form the basis of consciousness, intellect, personality, speech, understanding. In each of the large hemispheres, the following formations are distinguished: isolated accumulations (nuclei) of gray matter lying in the depths, which contain many important centers; a large array of white matter located above them; covering the hemispheres from the outside, a thick layer of gray matter with numerous convolutions, constituting the cerebral cortex.

Cerebellum also consists of a gray matter located in the depths, an intermediate array of white matter and an outer thick layer of gray matter, forming many convolutions. The cerebellum provides mainly coordination of movements.

Trunk The brain is formed by a mass of gray and white matter, not divided into layers. The trunk is closely connected with the cerebral hemispheres, cerebellum and spinal cord and contains numerous centers of sensory and motor pathways. The first two pairs of cranial nerves depart from the cerebral hemispheres, while the remaining ten pairs from the trunk. The trunk regulates such vital functions as breathing and blood circulation.

Scientists have calculated that the brain of a man is heavier than the brain of a woman by an average of 100 gm. They explain this by the fact that most men are much larger than women in terms of their physical parameters, that is, all parts of a man's body are larger than parts of a woman's body. The brain actively begins to grow even when the child is still in the womb. The brain reaches its "real" size only when a person reaches the age of twenty. At the very end of a person's life, his brain becomes a little lighter.

There are five main divisions in the brain:

1) telencephalon;

2) diencephalon;

3) midbrain;

4) hindbrain;

5) medulla oblongata.

If a person has suffered a traumatic brain injury, then this always negatively affects both his central nervous system and his mental state.

The "drawing" of the brain is very complex. The complexity of this "pattern" is predetermined by the fact that furrows and ridges go along the hemispheres, which form a kind of "gyrus". Despite the fact that this "drawing" is strictly individual, there are several common furrows. Thanks to these common furrows, biologists and anatomists have identified 5 lobes of the hemispheres:

1) frontal lobe;

2) parietal lobe;

3) occipital lobe;

4) temporal lobe;

5) hidden share.

Despite the fact that hundreds of works have been written on the study of the functions of the brain, its nature has not been fully elucidated. One of the most important mysteries that the brain “guesses” is vision. Rather, how and with what help we see. Many mistakenly assume that vision is the prerogative of the eyes. This is wrong. Scientists are more inclined to believe that the eyes simply perceive the signals that our environment sends us. Eyes pass them on "by authority". The brain, having received this signal, builds a picture, i.e. we see what our brain “shows” to us. Similarly, the issue with hearing should be resolved: it is not the ears that hear. Rather, they also receive certain signals that the environment sends us.

Spinal cord.

The spinal cord looks like a cord, it is somewhat flattened from front to back. Its size in an adult is approximately 41 to 45 cm, and its weight is about 30 gm. It is "surrounded" by the meninges and is located in the brain canal. Throughout its length, the thickness of the spinal cord is the same. But it has only two thickenings:

1) cervical thickening;

2) lumbar thickening.

It is in these thickenings that the so-called innervation nerves of the upper and lower extremities are formed. Dorsal brainis divided into several departments:

1) cervical;

2) thoracic region;

3) lumbar;

4) sacral department.

Located inside the spinal column and protected by its bone tissue, the spinal cord has a cylindrical shape and is covered with three membranes. On a transverse section, the gray matter has the shape of the letter H or a butterfly. Gray matter is surrounded by white matter. The sensory fibers of the spinal nerves end in the dorsal (posterior) sections of the gray matter - the posterior horns (at the ends of H facing the back). The bodies of motor neurons of the spinal nerves are located in the ventral (anterior) sections of the gray matter - the anterior horns (at the ends of H, remote from the back). In the white matter, there are ascending sensory pathways ending in the gray matter of the spinal cord, and descending motor pathways coming from the gray matter. In addition, many fibers in the white matter connect the different parts of the gray matter of the spinal cord.

Main and specific CNS function- the implementation of simple and complex highly differentiated reflective reactions, called reflexes. In higher animals and humans, the lower and middle sections of the central nervous system - the spinal cord, medulla oblongata, midbrain, diencephalon and cerebellum - regulate the activity of individual organs and systems of a highly developed organism, communicate and interact between them, ensure the unity of the organism and the integrity of its activity. The highest department of the central nervous system - the cerebral cortex and the nearest subcortical formations - mainly regulates the connection and relationship of the body as a whole with the environment.

The main features of the structure and function CNS

connected with all organs and tissues through the peripheral nervous system, which in vertebrates includes cranial nerves from the brain, and spinal nerves- from the spinal cord, intervertebral nerve nodes, as well as the peripheral part of the autonomic nervous system - nerve nodes, with nerve fibers approaching them (preganglionic) and departing from them (postganglionic) nerve fibers.

Sensory, or afferent, nervous adductor fibers carry excitation to the central nervous system from peripheral receptors; by diverting efferent (motor and autonomic) nerve fibers excitation from the central nervous system is sent to the cells of the executive working apparatus (muscles, glands, blood vessels, etc.). In all parts of the CNS there are afferent neurons that perceive stimuli coming from the periphery, and efferent neurons that send nerve impulses to the periphery to various executive organs.

Afferent and efferent cells with their processes can contact each other and make up two-neuron reflex arc, carrying out elementary reflexes (for example, tendon reflexes of the spinal cord). But, as a rule, interneurons, or interneurons, are located in the reflex arc between the afferent and efferent neurons. Communication between different parts of the central nervous system is also carried out with the help of many processes of afferent, efferent and intercalary neurons of these departments, forming intracentral short and long pathways. The CNS also includes neuroglial cells, which perform a supporting function in it, and also participate in the metabolism of nerve cells.

The brain and spinal cord are covered with membranes:

1) dura mater;

2) arachnoid;

3) soft shell.

Hard shell. The hard shell covers the outside of the spinal cord. In its shape, it most of all resembles a bag. It should be said that the outer hard shell of the brain is the periosteum of the bones of the skull.

Arachnoid. The arachnoid is a substance that is almost closely adjacent to the hard shell of the spinal cord. The arachnoid membrane of both the spinal cord and the brain does not contain any blood vessels.

Soft shell. The pia mater of the spinal cord and brain contains nerves and blood vessels, which, in fact, feed both brains.

autonomic nervous system

autonomic nervous system It is one of the parts of our nervous system. The autonomic nervous system is responsible for: the activity of the internal organs, the activity of the endocrine and external secretion glands, the activity of the blood and lymphatic vessels, and also, to some extent, the muscles.

The autonomic nervous system is divided into two sections:

1) sympathetic section;

2) parasympathetic section.

Sympathetic nervous system dilates the pupil, it also causes an increase in heart rate, an increase in blood pressure, expands the small bronchi, etc. This nervous system is carried out by sympathetic spinal centers. It is from these centers that peripheral sympathetic fibers begin, which are located in the lateral horns of the spinal cord.

parasympathetic nervous system is responsible for the activity of the bladder, genitals, rectum, and it also “irritates” a number of other nerves (for example, glossopharyngeal, oculomotor nerve). Such a "diverse" activity of the parasympathetic nervous system is explained by the fact that its nerve centers are located both in the sacral spinal cord and in the brain stem. Now it becomes clear that those nerve centers that are located in the sacral spinal cord control the activity of the organs located in the small pelvis; nerve centers located in the brain stem regulate the activity of other organs through a number of special nerves.

How is the control over the activity of the sympathetic and parasympathetic nervous system carried out? Control over the activity of these sections of the nervous system is carried out by special autonomic apparatus, which are located in the brain.

Diseases of the autonomic nervous system. The causes of diseases of the autonomic nervous system are as follows: a person does not tolerate hot weather or, conversely, feels uncomfortable in winter. A symptom may be that a person, when excited, quickly begins to blush or turn pale, his pulse quickens, he begins to sweat a lot.

It should be noted that diseases of the autonomic nervous system occur in people from birth. Many believe that if a person gets excited and blushes, then he is simply too modest and shy. Few people would think that this person has some kind of autonomic nervous system disease.

Also, these diseases can be acquired. For example, due to a head injury, chronic poisoning with mercury, arsenic, due to a dangerous infectious disease. They can also occur when a person is overworked, with a lack of vitamins, with severe mental disorders and experiences. Also, diseases of the autonomic nervous system can be the result of non-compliance with safety regulations at work with dangerous working conditions.

The regulatory activity of the autonomic nervous system may be impaired. Diseases can "mask" as other diseases. For example, with a disease of the solar plexus, bloating, poor appetite can be observed; with a disease of the cervical or thoracic nodes of the sympathetic trunk, chest pains can be observed, which can radiate to the shoulder. These pains are very similar to heart disease.

To prevent diseases of the autonomic nervous system, a person should follow a number of simple rules:

1) avoid nervous fatigue, colds;

2) observe safety precautions in production with hazardous working conditions;

3) eat well;

4) go to the hospital in a timely manner, complete the entire prescribed course of treatment.

Moreover, the last point, timely admission to the hospital and complete completion of the prescribed course of treatment, is the most important. This follows from the fact that delaying your visit to the doctor for too long can lead to the most unfortunate consequences.

Good nutrition also plays an important role, because a person "charges" his body, gives him new strength. Having refreshed, the body begins to fight diseases several times more actively. In addition, fruits contain many beneficial vitamins that help the body fight disease. The most useful fruits are in their raw form, because when they are harvested, many useful properties can disappear. A number of fruits, in addition to containing vitamin C, also have a substance that enhances the action of vitamin C. This substance is called tannin and is found in quinces, pears, apples, and pomegranates.

Development of the nervous system in ontogeny. Characteristics of the three-bubble and five-bubble stages of brain formation

ontogeny, or individual development The body is divided into two periods: prenatal (intrauterine) and postnatal (after birth). The first continues from the moment of conception and the formation of the zygote until birth; the second - from the moment of birth to death.

prenatal period in turn is divided into three periods: initial, embryonic and fetal. The initial (pre-implantation) period in humans covers the first week of development (from the moment of fertilization to implantation in the uterine mucosa). Embryonic (prefetal, embryonic) period - from the beginning of the second week to the end of the eighth week (from the moment of implantation to the completion of organ laying). The fetal (fetal) period begins from the ninth week and lasts until birth. At this time, there is an increased growth of the body.

postnatal period ontogenesis is divided into eleven periods: 1st - 10th day - newborns; 10th day - 1 year - infancy; 1-3 years - early childhood; 4-7 years - the first childhood; 8-12 years - the second childhood; 13-16 years - adolescence; 17-21 years old - youthful age; 22-35 years - the first mature age; 36-60 years - the second mature age; 61-74 years - old age; from 75 years old - senile age, after 90 years old - long-livers.

Ontogeny ends with natural death.

The nervous system develops from three main formations: neural tube, neural crest and neural placodes. The neural tube is formed as a result of neurulation from the neural plate - a section of the ectoderm located above the notochord. According to the theory of Shpemen's organizers, chord blastomeres are capable of secreting substances - inductors of the first kind, as a result of which the neural plate bends inside the body of the embryo and a neural groove is formed, the edges of which then merge, forming a neural tube. The closure of the edges of the neural groove begins in the cervical region of the body of the embryo, spreading first to the caudal part of the body, and later to the cranial.

The neural tube gives rise to the central nervous system, as well as neurons and gliocytes of the retina. Initially, the neural tube is represented by a multi-row neuroepithelium, the cells in it are called ventricular. Their processes facing the cavity of the neural tube are connected by nexuses, the basal parts of the cells lie on the subpial membrane. The nuclei of neuro-epithelial cells change their location depending on the phase of the cell life cycle. Gradually, towards the end of embryogenesis, ventricular cells lose their ability to divide and give rise to neurons and various types of gliocytes in the postnatal period. In some areas of the brain (germinal or cambial zones), ventricular cells do not lose their ability to divide. In this case, they are called subventricular and extraventricular. Of these, in turn, neuroblasts differentiate, which, no longer having the ability to proliferate, undergo changes during which they turn into mature nerve cells - neurons. The difference between neurons and other cells of their differon (cell row) is the presence of neurofibrils in them, as well as processes, while the axon (neuritis) appears first, and later - dendrites. The processes form connections - synapses. In total, the differon of the nervous tissue is represented by neuroepithelial (ventricular), subventricular, extraventricular cells, neuroblasts and neurons.

Unlike macroglial gliocytes, which develop from ventricular cells, microglial cells develop from the mesenchyme and enter the macrophage system.

The cervical and trunk parts of the neural tube give rise to the spinal cord, the cranial part differentiates into the head. The cavity of the neural tube turns into a spinal canal connected to the ventricles of the brain.

The brain undergoes several stages in its development. Its departments develop from the primary cerebral vesicles. At first there are three of them: front, middle and diamond-shaped. By the end of the fourth week, the anterior cerebral vesicle is divided into the rudiments of the telencephalon and diencephalon. Shortly thereafter, the rhomboid bladder also divides, giving rise to the hindbrain and medulla oblongata. This stage of brain development is called the stage of five brain bubbles. The time of their formation coincides with the time of the appearance of the three bends of the brain. First of all, a parietal bend is formed in the region of the middle cerebral bladder, its bulge is turned dorsally. After it, an occipital bend appears between the rudiments of the medulla oblongata and spinal cord. Its convexity is also turned dorsally. The last to form a bridge bend between the two previous ones, but it bends ventrally.

The cavity of the neural tube in the brain is transformed first into the cavity of three, then five bubbles. The cavity of the rhomboid bladder gives rise to the fourth ventricle, which is connected through the aqueduct of the midbrain (cavity of the middle cerebral bladder) with the third ventricle, formed by the cavity of the rudiment of the diencephalon. The cavity of the initially unpaired rudiment of the telencephalon is connected through the interventricular opening with the cavity of the rudiment of the diencephalon. In the future, the cavity of the terminal bladder will give rise to the lateral ventricles.

The walls of the neural tube at the stages of formation of the cerebral vesicles will thicken most evenly in the region of the midbrain. The ventral part of the neural tube is transformed into the legs of the brain (midbrain), gray tubercle, funnel, posterior pituitary gland (midbrain). Its dorsal part turns into a plate of the roof of the midbrain, as well as the roof of the third ventricle with the choroid plexus and the epiphysis. The lateral walls of the neural tube in the region of the diencephalon grow, forming visual tubercles. Here, under the influence of inductors of the second kind, protrusions are formed - eye vesicles, each of which will give rise to an eye cup, and later - the retina. Inducers of the third kind, located in the eyecups, affect the ectoderm above itself, which laces up inside the glasses, giving rise to the lens.

Central nervous system (CNS)- the main part of the nervous system of animals and humans, consisting of an accumulation of nerve cells (neurons) and their processes.

The central nervous system consists of the brain and spinal cord and their protective membranes. The outermost is the dura mater, under it is the arachnoid (arachnoid), and then the pia mater, fused with the surface of the brain. Between the soft and arachnoid membranes is the subarachnoid (subarachnoid) space containing the cerebrospinal (cerebrospinal) fluid, in which both the brain and the spinal cord literally float. The action of the buoyancy force of the fluid leads to the fact that, for example, the brain of an adult, having an average mass of 1500 g, actually weighs 50-100 g inside the skull. The meninges and cerebrospinal fluid also play the role of shock absorbers, softening all kinds of shocks and shocks that experiences the body and which could cause damage to the nervous system.

The CNS is made up of gray and white matter. Gray matter is made up of cell bodies, dendrites, and unmyelinated axons, organized into complexes that include countless synapses and serve as information processing centers for many of the functions of the nervous system. White matter consists of myelinated and unmyelinated axons, which act as conductors that transmit impulses from one center to another. The composition of gray and white matter also includes glial cells. CNS neurons form many circuits that perform two main functions: they provide reflex activity, as well as complex information processing in higher brain centers. These higher centers, such as the visual cortex (visual cortex), receive incoming information, process it, and transmit a response signal along the axons.

The result of the activity of the nervous system is one or another activity, which is based on the contraction or relaxation of muscles or the secretion or cessation of secretion of glands. It is with the work of muscles and glands that any way of our self-expression is connected. Incoming sensory information is processed by passing through a sequence of centers connected by long axons, which form specific pathways, such as pain, visual, auditory. Sensitive (ascending) pathways go in an ascending direction to the centers of the brain. Motor (descending) pathways connect the brain with the motor neurons of the cranial and spinal nerves. Pathways are usually organized in such a way that information (for example, pain or tactile) from the right side of the body goes to the left side of the brain and vice versa. This rule also applies to descending motor pathways: the right half of the brain controls the movements of the left half of the body, and the left half controls the right. There are a few exceptions to this general rule, however.

It consists of three main structures: the cerebral hemispheres, the cerebellum and the trunk.

The cerebral hemispheres - the largest part of the brain - contain higher nerve centers that form the basis of consciousness, intellect, personality, speech, and understanding. In each of the large hemispheres, the following formations are distinguished: isolated accumulations (nuclei) of gray matter lying in the depths, which contain many important centers; a large array of white matter located above them; covering the hemispheres from the outside, a thick layer of gray matter with numerous convolutions, constituting the cerebral cortex.

The cerebellum also consists of a deep gray matter, an intermediate array of white matter, and an outer thick layer of gray matter that forms many convolutions. The cerebellum provides mainly coordination of movements.

The brain stem is formed by a mass of gray and white matter, not divided into layers. The trunk is closely connected with the cerebral hemispheres, cerebellum and spinal cord and contains numerous centers of sensory and motor pathways. The first two pairs of cranial nerves depart from the cerebral hemispheres, the remaining ten pairs from the trunk. The trunk regulates such vital functions as breathing and blood circulation.

Located inside the spinal column and protected by its bone tissue, the spinal cord has a cylindrical shape and is covered with three membranes. On a transverse section, the gray matter has the shape of the letter H or a butterfly. Gray matter is surrounded by white matter. The sensory fibers of the spinal nerves end in the dorsal (posterior) sections of the gray matter - the posterior horns (at the ends of H facing the back). The bodies of the motor neurons of the spinal nerves are located in the ventral (anterior) sections of the gray matter - the anterior horns (at the ends of H, remote from the back). In the white matter, there are ascending sensory pathways ending in the gray matter of the spinal cord, and descending motor pathways coming from the gray matter. In addition, many fibers in the white matter connect the different parts of the gray matter of the spinal cord.

The main features of the structure and function The central nervous system is connected with all organs and tissues through the peripheral nervous system, which in vertebrates includes cranial nerves extending from the brain, and spinal nerves - from the spinal cord, intervertebral nerve nodes, as well as the peripheral part of the autonomic nervous system - nerve nodes, with nerve fibers approaching them (preganglionic) and departing from them (postganglionic) nerve fibers.

Sensitive, or afferent, nerve adductor fibers carry excitation to the central nervous system from peripheral receptors; along the efferent efferent (motor and autonomic) nerve fibers, excitation from the central nervous system is directed to the cells of the executive working apparatus (muscles, glands, blood vessels, etc.). In all parts of the CNS there are afferent neurons that perceive stimuli coming from the periphery, and efferent neurons that send nerve impulses to the periphery to various executive organs.

Afferent and efferent cells, with their processes, can contact each other and form a two-neuron reflex arc that performs elementary reflexes (for example, tendon reflexes of the spinal cord). But, as a rule, interneurons, or interneurons, are located in the reflex arc between the afferent and efferent neurons. Communication between different parts of the CNS is also carried out with the help of many processes of afferent, efferent and intercalary neurons of these parts, which form intracentral short and long pathways. The CNS also includes neuroglial cells, which perform a supporting function in it, and also participate in the metabolism of nerve cells.