What is the human central nervous system? Central nervous system. Structure of the nervous system

To cope with such various responsibilities, the human nervous system must have an appropriate structure.

The human nervous system is divided into:
- central nervous system;
- peripheral nervous system.

Purpose of the peripheral nervous system- connect the central nervous system with sensory receptors in the body and muscles. It includes the autonomic (autonomic) and somatic nervous systems.

Somatic nervous system designed to carry out voluntary, conscious sensory and motor functions. Its task is to transmit sensory signals caused by external stimuli to the central nervous system and control movements corresponding to these signals.

Autonomic nervous system- this is a kind of “autopilot” that automatically maintains the operating modes of the blood vessels of the heart, respiratory organs, digestion, urination and endocrine glands. The activity of the autonomic nervous system is subordinate to the brain centers of the human nervous system.

Human nervous system:
- Divisions of the nervous system
1) Central
- Brain
- Spinal cord
2) Peripheral
- Somatic system
- Vegetative (autonomous) system
1) Sympathetic system
2) Parasympathetic system

The autonomic system is divided into the sympathetic and parasympathetic nervous systems.

Sympathetic nervous system- This is a weapon of human self-defense. In situations that require a quick response (especially in situations of danger), the sympathetic nervous system:
- inhibits the activity of the digestive system as irrelevant at the moment (in particular, it reduces blood circulation in the stomach);
- increases the content of adrenaline and glucose in the blood, thereby dilating the blood vessels of the heart, brain and skeletal muscles;
- mobilizes the heart, increasing blood pressure and the rate of blood clotting in order to avoid possible large blood losses;
- dilates the pupils and eye slits, forming appropriate facial expressions.

Parasympathetic nervous system comes into play when the tense situation subsides and a time of peace and relaxation begins. All processes caused by the action of the sympathetic system are restored. The normal functioning of these systems is characterized by their dynamic equilibrium. A disruption of this balance occurs when one of the systems is overexcited. With prolonged and frequent states of overexcitation of the sympathetic system, there is a threat of chronic increase in blood pressure (hypertension), angina pectoris and other pathological disorders.

In case of overexcitation of the parasympathetic system, gastrointestinal diseases may appear (the occurrence of attacks of bronchial asthma and exacerbation of ulcerative pain during night sleep are explained by increased activity of the parasympathetic system and inhibition of the sympathetic system at this time of day).

There is the possibility of volitional regulation of autonomic functions using special techniques of suggestion and self-hypnosis (hypnosis, autogenic training, etc.). However, in order to avoid causing harm to the body (and psyche), this requires caution and conscious mastery of psychological technologies of this kind.

The central nervous system includes:
- brain;
- spinal cord.

Anatomically, they are located in the skull and spine. The bone tissues of the skull and spine provide protection to the brain from physical injury.

The spinal cord is a long column of nervous tissue that runs through the spinal canal, from the second lumbar vertebra to the medulla oblongata. It solves two main problems:
- transmits sensory information from peripheral receptors to the brain;
- provides the body's responses to external and internal signals through activation of the muscular system. The spinal cord is formed by 31 identical blocks ~ segments connected to various parts of the human torso. Each segment consists of gray and white matter. White matter forms the ascending, descending and intrinsic nerve pathways. The first transmit information to the brain, the second - from the brain to various parts of the body, the third - from segment to segment.

The structure of the gray matter is formed by the nuclei of the spinal nerves, extending from each of the segments. In turn, each spinal nerve consists of a sensory and a motor nerve. The first perceives sensory information from receptors of internal organs, muscles and skin. The second transmits motor excitation from the spinal nerves to the periphery of the human body.

The brain is the highest authority of the nervous system. This is the largest section of the central nervous system. Brain weight is not an informative indicator of the level of intellectual development of its owner. So, in relation to the body, the human brain is 1/45, the monkey’s brain is 1/25, the whale’s brain is 1/10,000. The absolute weight of the brain in men is about 1400 g, in women - 1250 g.

Brain mass changes throughout a person's life. Starting with a weight of 350 g (in newborns), the brain “gains” its maximum weight by age 25, then maintains it constant until the age of 50, and then begins to “lose weight” by an average of 30 g in each subsequent decade. All these parameters depend on a person’s belonging to a particular race (however, there is no correlation with the level of intelligence). For example, the maximum brain weight of a Japanese is observed at 30-40 years, for a European - at 20-25 years.

The brain consists of the forebrain, midbrain, hindbrain and medulla oblongata.

Modern ideas associate the development of the human brain at three levels:
- highest level - forebrain;
- middle level - midbrain;
- the lowest level is the hindbrain.

Forebrain. All components of the brain work together, but the “central control panel” of the nervous system is located in the anterior part of the brain, consisting of the cerebral cortex, diencephalon and olfactory brain (Fig. 4). This is where most of the neurons are located and strategic tasks for managing processes, as well as commands for their execution, are formed. The implementation of commands is undertaken by the middle and lower levels. At the same time, commands from the cerebral cortex can be innovative and completely unusual. The lower levels work out these commands according to the familiar, “well-worn” programs for humans. This “division of labor” has developed historically.

Representatives of the materialistic concept argue that the forebrain arose as a result of the evolution of the sense of smell. At the moment, it controls instinctive (genetically determined), individual and collective (determined by work activity and speech) forms of human behavior. The collective form of behavior caused the appearance of new superficial layers of the cerebral cortex. There are six such layers in total, each of which consists of the same type of nerve cells, having their own shape and orientation. According to the time it happened<дения принято различать древнюю, старую и новую кору. Древняя кора занимает около 0,6 % площади всей коры и состоит из одного слоя нейронов. Площадь старой коры - 2,6 %. Остальная площадь принадлежит новой коре.

Externally, the bark resembles the kernel of a walnut: a wrinkled surface with numerous convolutions and grooves. This configuration is the same for all people. Beneath the cortex are the right and left hemispheres of the brain, which account for about 80% of the weight of the entire brain. The hemispheres are filled with axons connecting cortical neurons with neurons in other parts of the brain. Each hemisphere of the brain consists of jointly functioning frontal, temporal, parietal and occipital lobes.

In connection with the role played by the cerebral cortex in human mental life, it is advisable to consider in more detail the functions it performs.

In the cortex, several functional zones (centers) are conventionally distinguished, associated with the performance of certain functions.

Each of the sensory (primary projective) zones receives signals from “its” sense organs and is directly involved in the formation of sensations. The visual and auditory sensory areas are located separately from the others. Damage to sensory areas causes loss of a certain type of sensitivity (hearing, vision, etc.).

Motor zones move different parts of the body. By irritating areas of the motor zones with a weak electric current, it is possible to force various organs to move (even against the will of a person) (lips stretch in a smile, bend an arm, etc.).

Damage to areas of this zone is accompanied by partial or complete paralysis.

The so-called basal ganglia, located under the frontal lobes, take part in the regulation of voluntary and involuntary movements. The consequences of their damage are convulsions, tics, twitching, mask-like appearance of the face, muscle tremors, etc.

Associative (integrative) zones are capable of simultaneously responding to signals from several sense organs and forming holistic perceptual images (perception). These zones do not have clearly defined boundaries (at least, the boundaries have not yet been established). When associative zones are damaged, signs of a different kind appear: sensitivity to a certain type of stimulus (visual, auditory, etc.) is preserved, but the ability to correctly assess the meaning of the current stimulus is impaired. So:
- damage to the visual associative zone leads to “verbal blindness”, when vision is preserved, but the ability to understand what you see is lost (a person can read a word, but not understand its meaning);
- if the auditory associative zone is damaged, a person hears, but does not understand the meaning of words (verbal deafness);
- disruption of the tactile associative zone leads to the fact that a person is unable to recognize objects by touch;
damage to the associative zones of the frontal lobe leads to loss of the ability to plan and predict events while maintaining memory and skills;
- injuries to the frontal lobe sharply change the personality's character towards intemperance, rudeness and promiscuity while maintaining other abilities necessary for the individual's daily life.

Strictly speaking, autonomous speech centers do not exist. Here they often talk about the center of auditory perception of speech (Wernicke's center) and the motor center of speech (Broca's center). The representation of the speech function in most people is located in the left hemisphere in the region of the third gyrus of the cortex. This is evidenced by facts of disruption of speech formation processes when the frontal lobe is damaged and loss of speech understanding when the posterior parts of the lobe are damaged. The “capture” of speech functions (and with it the functions of logical thinking, reading and writing) by the left hemisphere is called functional asymmetry of the brain.

The right hemisphere inherited processes associated with the regulation of feelings. In this regard, the right hemisphere is involved in the formation of a holistic image of an object. The left one is called upon to analyze the little things when perceiving an object, that is, it forms an image of the object consistently, in detail. This is the “press secretary” of the brain. But information processing occurs in the close collaboration of both hemispheres: as soon as one hemisphere is denied work, the other turns out to be helpless.

The diencephalon supervises the activities of the sensory organs and regulates all autonomic functions. Its composition:
- thalamus (visual thalamus);
- hypothalamus (subtubercular region).

The thalamus (visual thalamus) is a sensory control point for information flows, the largest “transport” node of the nervous system. The main function of the thalamus is to receive information from sensory neurons (from the eyes, ears, tongue, skin, internal organs, except smell) and transmit it to the higher parts of the brain.

The hypothalamus (subtubercular region) controls the functioning of internal organs, endocrine glands, metabolic processes, and body temperature. This is where a person’s emotional states are formed. The hypothalamus influences human sexual behavior.

The olfactory brain is the smallest part of the forebrain, providing the function of smell, marked by the gray hairs of thousands of years of evolution of the human psyche.

The midbrain is located between the hindbrain and the intermediate brain (see Fig. 3). Here are the primary centers of vision and hearing, as well as nerve fibers connecting the spinal and medulla oblongata with the cerebral cortex. The midbrain includes a significant part of the limbic system (visceral brain). The elements of this system are the hippocampus and the amygdala.

The medulla oblongata is the lowest part of the brain. Anatomically, it is a continuation of the spinal cord. The “responsibilities” of the medulla oblongata include:
- coordination of movements, regulation of breathing, heartbeat, tone of blood vessels, etc.;
- regulation by reflex acts of chewing, swallowing, sucking, vomiting, blinking and coughing;
- control of body balance in space.

The hindbrain is located between the midbrain and the medulla oblongata. Consists of the cerebellum and the pons. The pons contains the centers of the auditory, vestibular, skin and muscle sensory systems, the autonomic centers for the regulation of the lacrimal and salivary glands. He is involved in the implementation and development of complex forms of movements.

An important role in the functioning of the human nervous system is played by the reticular (mesh) formation, which is located in the spinal cord, medulla oblongata and hindbrain. Its influence extends to brain activity, the state of the cortex and subcortical structures of the brain, cerebellum, and spinal cord. This is the source of the body’s activity and its performance. Its main functions:
- maintaining a wakeful state;
- increased tone of the cerebral cortex;
- selective inhibition of the activity of certain areas of the brain (auditory and visual centers of subcortical structures), which is important for the control of attention;
- formation of standard adaptive forms of response to familiar external stimuli;
- formation of indicative reactions to unusual external stimuli, on the basis of which reactions of the first type can be formed and the normal functioning of the body can be ensured.

Disruption of this formation leads to disruptions in the body's biorhythms. For example, a person cannot fall asleep for a long time or, conversely, sleep becomes very long.

The hippocampus significantly influences memory processes. Disruption of its functioning leads to deterioration or complete loss of short-term memory. Long-term memory is not affected. It is believed that the hippocampus is involved in the processes of transferring information from short-term memory to long-term memory. In addition, it participates in the formation of emotions, which ensures reliable memorization of the material.

The tonsils are two bundles of neurons that influence feelings of aggression, rage and fear. However, the tonsils are not the center of these feelings. Aristotle also tried to localize feelings (the soul emits a thought, the body gives birth to various sensations, and the heart is the seat of feelings, passions, mind and voluntary movements). His idea was supported by Thomas Aquinas. Descartes argued that feelings of joy and danger are generated by the pineal gland, which then transmits them to the soul, brain and heart. I.M. Sechenov’s hypothesis is that emotions are a systemic phenomenon.

The first experimental attempts to link emotions with the work of certain parts of the brain (to localize emotions) were made by V. M. Bekhterev. By stimulating areas of the thalamus of birds, he analyzed the emotional content of their motor reactions. Subsequently, V. Cannon and P. Bard (USA) gave the thalamus a decisive role in the formation of emotions. Even angrier, E. Gelgorn and J. Lufborrow came to the conclusion that the main center for the formation of emotions is the hypothalamus.

Experimental studies conducted by S. Olds and P. Milner (USA) on rats made it possible to identify their “heaven” and “hell” zones. It turned out that about 35% of brain points are responsible for the formation of feelings of pleasure, 5% cause feelings of displeasure and 60% remain neutral regarding these feelings. Naturally, these results cannot be completely transferred to the human psyche.

As we penetrated into the secrets of the psyche, the opinion became increasingly stronger that the organization of emotions is a widely branched system of nervous formations. At the same time, the main functional role of negative emotions is to preserve man as a species, and positive ones - to acquire new properties. If negative emotions were not necessary for survival, they would simply disappear from the psyche. The main control and regulation of emotional behavior is carried out by the frontal lobes of the cerebral cortex.

The search for areas responsible for certain mental states and processes is still underway. Moreover, the localization problem has grown into a psychophysiological problem.

1. Management of the musculoskeletal system. The central nervous system regulates muscle tone and, through its redistribution, maintains natural posture, and if it is disturbed, restores it, initiates all types of motor activity (physical work, physical education, sports, any movement of the body).

2. Regulation of internal organs carried out by the autonomic nervous system and endocrine glands; ensures the intensity of their functioning according to the needs of the body in various conditions of its life.

3. Providing consciousness and all types of mental activity. Mental activity is an ideal, subjectively conscious activity of the body, carried out with the help of neurophysiological processes. I.P. Pavlov introduced the concept of higher and lower nervous activity. Higher nervous activity - This is a set of neurophysiological processes that ensure consciousness, subconscious processing of information and purposeful behavior of the organism in the environment. Mental activity is carried out with the help of higher nervous activity and occurs consciously, i.e. during wakefulness, regardless of whether it is accompanied by physical work or not. Higher nervous activity occurs during wakefulness and sleep (see sections 15.8, 15.9, 15.10). Lower nervous activity is a set of neurophysiological processes that ensure the implementation of unconditioned reflexes.

4. Formation of interaction of the organism with the environment. This is realized, for example, by avoiding or getting rid of unpleasant stimuli (defensive reactions of the body), regulating the metabolic rate when the ambient temperature changes. Changes in the internal environment of the body, perceived subjectively in the form of sensations, also induce the body to one or another purposeful motor activity. For example, in the case of a lack of water and with an increase in the osmotic pressure of body fluids, thirst arises, which initiates behavior aimed at searching for and receiving water. Any activity of the central nervous system itself is ultimately realized through the functioning of individual cells.

FUNCTIONS OF CNS AND CSF CELLS,

CLASSIFICATION OF CNS NEURONS,

THEIR MEDIATORS AND RECEPTORS

The human brain contains about 50 billion nerve cells, the interaction between which is carried out through many synapses, the number of which is thousands of times greater than the number of cells themselves (10 15 -10 16), since their axons are divided many times dichotomously, therefore one neuron can form up to a thousand synapses with other neurons. Neurons also exert their influence on organs and tissues through synapses.

A. Nerve cell (neuron) is a structural and functional unit of the central nervous system, it consists of a soma (cell body with poisonous

rum) and processes, representing a large number of dendrites and one axon (Fig. 5.5). The resting potential (RP) of a neuron is 60-80 mV, the action potential (AP) is 80-110 mV. The soma and dendrites are covered with nerve endings - synaptic boutons and processes of glial cells. On one neuron, the number of synaptic boutons can reach 10 thousand (see Fig. 5.5). The axon starts from the cell body with an axon hillock. The diameter of the cell body is 10-100 microns, the axon - 1-6 microns, at the periphery the length of the axon can reach a meter or more. Neurons in the brain form columns, nuclei, and layers that perform specific functions.

Clumps of cells form the gray matter of the brain. Unmyelinated and myelinated nerve fibers (dendrites and axons of neurons) pass between the cells.

Functions of a nerve cell are receiving, processing and storing information, transmitting signals to other nerve cells, regulating the activity of effector cells of various organs and tissues of the body. It is advisable to highlight the following functional structures of a neuron.

1. The structures that ensure the synthesis of macromolecules are the soma (neuron body), which performs a trophic function in relation to processes (axon and dendrites) and effector cells. The process, deprived of connection with the body of the neuron, degenerates. Macromolecules are transported along the axon and dendrites.

2. Structures that receive impulses from other nerve cells are the body and dendrites of the neuron with spines located on them, occupying up to 40% of the surface of the neuron’s soma and dendrites. Moreover, if the spines do not receive impulses, they disappear. Impulses can also arrive at the end of the axon - axo-axon synapses, for example, in the case of presynaptic inhibition.

3. The structures where the action potential usually arises (AP generator point) is the axon hillock.

4. Structures that conduct excitation to another neuron or to an effector - an axon.

5. Structures that transmit impulses to other cells are synapses.

B. Classification of CNS neurons. Neurons are divided into the following main groups.

1. Depending on the part of the central nervous system They secrete neurons of the somatic and autonomic nervous systems.

2. By source or direction of information neurons are divided into: a) afferent, perceiving information about the external and internal environment of the body with the help of receptors and transmitting it to the overlying parts of the central nervous system; b) efferent, transmitting information to working organs - effectors; nerve cells innervating effectors are sometimes called effector cells; effector neurons of the spinal cord (motoneurons) are divided into a-iu-motoneurons; V) insertion(interneurons) that provide interaction between neurons of the central nervous system.

3. According to the mediator, released in axon terminals, adrenergic, cholinergic, serotonergic, etc. neurons are distinguished.

4. By influence- excitatory and inhibitory.

IN. Glial cells (neuroglia - “nerve glue”) are more numerous than neurons, accounting for about 50% of the volume of the central nervous system. They are capable of dividing throughout their lives. The size of glial cells is 3-4 times smaller than nerve cells; with age, their number increases (the number of neurons decreases). The cell bodies of neurons, like their axons, are surrounded by glial cells. Glial cells perform several functions: supporting, protective, insulating, metabolic (supplying neurons with nutrients). Microglial cells are capable of phagocytosis, a rhythmic change in their volume (the period of “contraction” is 1.5 minutes, the period of “relaxation” is 4 minutes). Cycles of volume change are repeated every 2-20 hours. It is believed that pulsation promotes the movement of axoplasm in neurons and affects the flow of intercellular fluid. The membrane potential of neuroglial cells is 70-90 mV, but they do not generate APs; only local currents arise, electrotonically spreading from one cell to another. Excitation processes in neurons and electrical phenomena in glial cells appear to interact."

G. Liquor - a colorless transparent liquid that fills the cerebral ventricles, the spinal canal and the subarachnoid space. Its origin is associated with the interstitial fluid of the brain; a significant part of the cerebrospinal fluid is formed by the choroid plexuses of the ventricles of the brain. Direct nutritious The environment of brain cells is the interstitial fluid, into which the cells also secrete the products of their metabolism. Liquor is a combination of blood plasma filtrate and interstitial fluid: it contains about 90% water and about 10% dry residue (2% organic, 8% inorganic substances).

D. Mediators and receptors of CNS synapses. The mediators of CNS synapses are many chemical substances that are structurally heterogeneous (about 30 biologically active substances have been discovered in the brain to date). The substance from which the mediator is synthesized (the precursor of the mediator) enters the neuron or its ending from the blood or cerebrospinal fluid, as a result of biochemical reactions under the action of enzymes in the nerve endings, it is converted into the corresponding mediator and accumulates in synaptic vesicles. According to their chemical structure, mediators can be divided into several groups, the main of which are amines, amino acids, and polypeptides. A fairly widespread mediator is acetylcholine.

According to Dale's principle,one neuron synthesizes and uses the same transmitter or the same transmitters in all branches of its axon(“one neuron - one transmitter”). In addition to the main mediator, as it turned out, others can be released at the axon endings - accompanying mediators (co-mediators), playing a modulating role and acting more slowly. However, in the spinal cord there are two fast-acting transmitters in one inhibitory neuron - GABA and glycine, and even one inhibitory (GABA) and one excitatory (ATP). Therefore, Dale’s principle in the new edition first sounded: “One neuron - one fast transmitter”, and then: “One neuron - one fast synaptic effect” (other options are also assumed).

Effect of action the mediator depends mainly on the properties of the postsynaptic membrane and second messengers. This phenomenon is especially clearly demonstrated when comparing the effects of individual mediators in the central nervous system and in the peripheral synapses of the body. Acetylcholine, for example, in the cerebral cortex with microapplications to different neurons can cause excitation and inhibition, in the synapses of the heart - inhibition, in the synapses of the smooth muscles of the gastrointestinal tract - excitation. Catecholamines stimulate cardiac activity, but inhibit contractions of the stomach and intestines.

5.7. MECHANISM OF CNS NEURON EXCITATION

In any chemical synapses (CNS, autonomic ganglia, neuromuscular) the mechanisms of signal transmission are generally similar (see section 2.1). However, there are characteristic features in the excitation of CNS neurons, the main ones of which are the following.

1. To excite a neuron (the occurrence of an action potential), a flow of afferent impulses and their interaction are necessary. This is explained by the fact that one impulse arriving at the neuron causes a small excitatory postsynaptic potential (EPSP, Fig. 5.6) - only 0.05 mV (miniature EPSP). One vial contains up to several tens of thousands of mediator molecules, such as acetylcholine. Considering that the threshold potential of a neuron is 5-10 mV, it is clear that many impulses are required to excite a neuron.

2. The place of origin of generator EPSPs that cause AP of the neuron. The vast majority of neuronal synapses are located on the dendrites of the neuron. However, synaptic contacts most effectively cause excitation of a neuron,

located on the body of the neuron. This is due to the fact that the postsynaptic membranes of these synapses are located in close proximity to the site primary occurrence of PD, located in the axon hillock. The proximity of somatic synapses to the axon hillock ensures the participation of their EPSPs in the mechanisms of AP generation. In this regard, some authors suggest calling them generator synapses.

3. The generator point of the neuron, i.e. place of occurrence of PD, - axon hillock. There are no synapses on it; a distinctive feature of the axon hillock membrane is high excitability, 3-4 times higher than the excitability of the soma-dendritic membrane of the neuron, which is explained by the higher concentration of Na channels on the axon hillock. EPSPs electrically reach the axon hillock, ensuring here a decrease in the membrane potential to a critical level. At this moment, an action potential arises. The action potential arising in the axon hillock, on the one hand, passes orthodromically to the axon, on the other, antidromically to the body of the neuron.

4. The role of dendrites in the occurrence of excitation is still debated. It is believed that many EPSPs arising on dendrites electrotonically control the excitability of the neuron. In this regard, dendritic synapses are called modulatory synapses.

5.8. CHARACTERISTICS OF EXCITATION SPREAD IN THE CNS

The peculiarities of the spread of excitation in the central nervous system are explained by its neural structure - the presence of chemical synapses, multiple branching of neuron axons, and the presence of closed neural pathways. These features are the following.

1. One-way propagation of excitation in neural circuits, in reflex arcs. The one-way propagation of excitation from the axon of one neuron to the body or dendrites of another neuron, but not vice versa, is explained by the properties of chemical synapses, which conduct excitation in only one direction.

2. Slow spread of excitation in the central nervous system in comparison with a nerve fiber is explained by the presence of many chemical synapses along the paths of excitation propagation. The total delay in the transmission of excitation in a neuron before the occurrence of an AP reaches a value of about 2 ms.

3. Irradiation (divergence) of excitation V CNS is explained by the branching of neuron axons, their ability to establish numerous connections with other neurons, and the presence of interneurons, the axons of which also branch (Fig. 5.7 - A).

4. Convergence of excitation (the principle of a common final path) - the convergence of excitation of different origins along several paths to the same neuron or neural pool (the Sherrington funnel principle). This is explained by the presence of many axon collaterals, intercalary neurons, and also by the fact that there are several times more afferent pathways than efferent neurons. One CNS neuron can have up to 10,000 synapses, and motor neurons can have up to 20,000 (Fig. 5.7 - B).

5. Circulation of excitation along closed neural circuits, which can last for minutes or even hours (Fig. 5.8).

6. Spread of excitation in the central nervous system easily blocked by pharmacological drugs, which is widely used in clinical practice. Under physiological conditions, restrictions on the spread of excitation throughout the central nervous system are associated with the activation of neurophysiological mechanisms of neuronal inhibition.

The considered features of the propagation of excitation make it possible to approach the understanding of the distinctive properties of nerve centers.

PROPERTIES OF NERVE CENTERS

The properties of nerve centers discussed below are associated with certain features of the propagation of excitation in the central nervous system, the special properties of chemical synapses and the properties of nerve cell membranes. The main properties of nerve centers are the following.

A. Inertia - the relatively slow emergence of excitation of the entire complex of neurons of the center when impulses arrive to it and the slow disappearance of excitation of the neurons of the center after the cessation of input impulses. The inertia of the centers is associated with the summation of excitation and aftereffect.

Summation phenomenon excitation in the central nervous system was discovered by I.M. Sechenov (1868) in an experiment on a frog: irritation of a frog’s limb with weak, rare impulses does not cause a reaction, and more frequent irritations with the same weak impulses are accompanied by a response - the frog makes a jump. Distinguish temporal (sequential) and spatial summation(Fig. 5.9).

Aftereffect - this is the continuation of excitation of the nerve center after the cessation of impulses reaching it along the afferent nerve pathways. The main reason for the aftereffect is the circulation of excitation along closed neural circuits (see Fig. 5.8), which can last for minutes or even hours.

B. Background activity of nerve centers (tone) explained: 1) spontaneous activity of CNS neurons; 2) humoral influences of biologically active substances(metabolites, hormones, mediators, etc.) circulating in the blood and affecting the excitability of neurons; 3) afferent impulses from various reflexogenic zones; 4) summation of miniature potentials, arising as a result of the spontaneous release of transmitter quanta from axons forming synapses on neurons; 5) circulation of excitation in the central nervous system. Meaning background activity of nerve centers is to provide some

the initial level of the active state of the center and effectors. This level can increase or decrease depending on fluctuations in the total activity of neurons in the nerve center-regulator.

IN. Transformation of the rhythm of excitation - this is a change in the number of impulses arising in the neurons of the center at the output relative to the number of impulses arriving at the input of this center. Transformation of the rhythm of excitation is possible both in the direction of increase and decrease. An increase in the number of impulses arising in the center in response to afferent impulses is facilitated by the irradiation of the excitation process and the aftereffect. The decrease in the number of impulses in the nerve center is explained by a decrease in its excitability due to the processes of pre- and postsynaptic inhibition, as well as an excessive flow of afferent impulses. With a large flow of afferent influences, when all the neurons of the center or neuronal pool are already excited, a further increase in afferent inputs does not increase the number of excited neurons.

G. Greater sensitivity of the central nervous system to changes in the internal environment, for example, to changes in blood glucose levels, blood gas composition, temperature, and various pharmacological drugs administered for therapeutic purposes. Neuron synapses react first. CNS neurons are especially sensitive to a lack of glucose and oxygen. When glucose levels drop 2 times below normal (up to 50% of normal), seizures may occur. Severe consequences for the central nervous system are caused by a lack of oxygen in the blood. Stopping blood flow for just 10 seconds leads to obvious disturbances in brain function, and the person loses consciousness. Stopping blood flow for 8-12 minutes causes irreversible disturbances in brain activity - many neurons die, primarily cortical ones, which leads to serious consequences.

D. Plasticity of nerve centers - the ability of nerve elements to rearrange functional properties. The main manifestations of plasticity are as follows.

1. Synaptic relief - this is an improvement in conduction at synapses after short stimulation of afferent pathways. The severity of relief increases with increasing frequency of the pulses, it is greatest when the pulses arrive at intervals of several milliseconds.

The duration of synaptic relief depends on the properties of the synapse and the nature of the irritation - after single stimuli it is small, after an irritating series relief in the central nervous system can

last from several minutes to several hours. Apparently, the main reason for the occurrence of synaptic facilitation is the accumulation of Ca 2+ in presynaptic terminals, since Ca 2+, which enters the nerve ending during AP, accumulates there, since the ion pump does not have time to remove it from the nerve ending. Accordingly, the release of the transmitter increases with the occurrence of each impulse in the nerve ending, and the EPSP increases. Besides, with frequent use of synapses the synthesis of receptors and mediators is accelerated and the mobilization of mediator vesicles is accelerated; on the contrary, with rare use of synapses, the synthesis of mediators decreases - the most important property of the central nervous system. Therefore, the background activity of neurons contributes to the occurrence of excitation in the nerve centers. Meaning synaptic facilitation lies in the fact that it creates the prerequisites for improving information processing processes on neurons of nerve centers, which is extremely important, for example, for learning during the development of motor skills and conditioned reflexes.

2. Synaptic depression - this is a deterioration in conduction at synapses as a result of prolonged sending of impulses, for example, with prolonged stimulation of the afferent nerve (central fatigue). Fatigue nerve centers was demonstrated by N. E. Vvedensky in an experiment on a frog preparation with repeated reflex causing contraction of the gastrocnemius muscle by irritating the p. tlianas and p. regones. In this case, rhythmic stimulation of one nerve causes rhythmic contractions of the muscle, leading to a weakening of the force of its contraction until the complete absence of contraction. Switching stimulation to another nerve immediately causes a contraction of the same muscle, which indicates the localization of fatigue not in the muscle, but in the central part of the reflex arc (Fig. 5.10). The weakening of the center’s reaction to afferent impulses is expressed in a decrease in postsynaptic potentials. It is explained by the consumption of the mediator, the accumulation of metabolites, in particular, the acidification of the environment during long-term conduction of excitation along the same neural circuits.

3. Dominant - a persistent dominant focus of excitation in the central nervous system, subordinating the functions of other nerve centers. Dominant is a more persistent phenomenon of relief. The phenomenon of dominance was discovered by A. A. Ukhtomsky (1923) in experiments with irritation of the motor zones of the cerebrum and observation of the flexion of an animal’s limb. As it turned out, if you irritate the cortical motor area against the background of an excessive increase in the excitability of another

nerve center, limb flexion may not occur. Instead of flexing the limb, irritation of the motor zone causes a reaction of those effectors whose activity is controlled by the dominant, i.e., the currently dominant nerve center in the central nervous system.

The dominant focus of excitation has a number of special properties, the main ones are the following: inertia, persistence, increased excitability, the ability to “attract” to oneself excitations radiating through the central nervous system, the ability to exert a depressing effect on competing centers and other nerve centers.

Meaning The dominant focus of excitation in the central nervous system is that on its basis specific adaptive activity is formed, aimed at achieving useful results necessary to eliminate the causes that maintain a particular nerve center in a dominant state. For example, on the basis of the dominant state of the hunger center, food-procuring behavior is realized, and on the basis of the dominant state of the thirst center, behavior aimed at searching for water is triggered. The successful completion of these behavioral acts ultimately eliminates the physiological causes of the dominant state of the hunger or thirst centers. The dominant state of the central nervous system ensures the automated execution of motor reactions.

4. Compensation for impaired functions after damage to one or another center - also the result of the manifestation of plasticity of the central nervous system. Clinical observations of patients in whom, after hemorrhages in the brain substance, the centers regulating muscle tone and the act of walking were damaged are well known. However, over time, it was noted that the paralyzed limb in patients gradually begins to be involved in motor activity, while the tone of its muscles normalizes. The impaired motor function is partially and sometimes completely restored due to the greater activity of the remaining neurons and the involvement in this function of other “scattered” neurons in the cerebral cortex with similar functions. This is facilitated by regular (persistent, persistent) passive and active movements.

INHIBITION IN THE CNS

Braking- This is an active nervous process, the result of which is the cessation or weakening of excitation. Inhibition is secondary to the process of excitation, since it always occurs as a consequence of excitation.

Inhibition in the central nervous system opened I. M. Sechenov (1863). In an experiment on a thalamic frog, he determined the latent time of the flexion reflex when the hind limb was immersed in a weak solution of sulfuric acid. It has been shown that the latent time of the reflex increases significantly if a crystal of table salt is first placed on the visual thalamus. The discovery of I.M. Sechenov served as an impetus for further studies of inhibition in the central nervous system, and two mechanisms of inhibition were discovered: post- and presynaptic.

A. Postsynaptic inhibition occurs on the postsynaptic membranes of the neuron as a result hyperpolarizing postsynaptic potential, which reduces the excitability of the neuron and inhibits its ability to respond to exciting influences. For this reason, the evoked hyperpolarization potential was called inhibitory postsynaptic potential, IPSP"(see Fig. 5.6). The amplitude of the IPSP is 1-5 mV, it is capable of summation.

The excitability of the cell from IPSP (hyperpolarizing postsynaptic potential) decreases because the threshold potential (MO) increases, since E cr (critical level of depolarization, CUD) remains at the same level, and the membrane potential (E) increases. IPSP occurs under the influence and amino acid

You glycine, and GABA - gamma-aminobutyric acid. In the spinal cord, glycine is secreted by special inhibitory cells (Renshaw cells) in the synapses formed by these cells on the membrane of the target neuron. Acting on the ionotropic receptor of the postsynaptic membrane, glycine increases its permeability to SG, while SG enters the cell according to a concentration gradient contrary to the electrical gradient, resulting in hyperpolarization. In a chlorine-free environment, the inhibitory role of glycine is not realized. The reactivity of a neuron to excitatory impulses is a consequence of the algebraic summation of IPSPs and EPSPs, and therefore in the area of ​​the axon hillock the membrane does not depolarize to a critical level. When GABA acts on the postsynaptic membrane, IPSP develops as a result of the entry of SG into the cell or the release of K + from the cell. Concentration gradients of K+ ions during the development of neuronal inhibition are supported by the Na/K-pump, and of SG ions by the SG-pump. Types of postsynaptic inhibition are presented in Fig. 5.11.

B. Presynaptic inhibition develops in presynaptic endings. Wherein membrane potential and excitability of the studied neurons do not change or a low-amplitude EPSP is recorded, which is insufficient for the occurrence of an AP (Fig. 5.12). Excitation is blocked in the presi"naptic endings due to depolarization their. At the source of depolarization the process of propagation of excitation is disrupted, therefore, incoming impulses, not being able to pass through the depolarization zone in the usual quantity and normal amplitude, do not ensure the release of the transmitter into the synaptic cleft in sufficient quantity, so the neuron is not excited, its functional state, naturally, remains unchanged. Depolarization of the presynaptic terminal is caused by special inhibitory intercalary cells, the axons of which form

there are synapses on the presynaptic terminals of the target axon(see Figure 5.12). Inhibition (depolarization) after one afferent volley lasts 300-400 ms; the mediator is gamma-aminobutyric acid (GABA), which acts on GABA receptors.

Depolarization is a consequence of increased permeability to SG, causing it to leave the cell according to an electrical gradient. This proves that the membranes of presynaptic terminals contain a chloride pump that ensures the transport of SG into the cell against the electrical gradient.

Types of presynaptic inhibition insufficiently studied. Apparently, the same options exist as for postsynaptic inhibition. In particular, in Fig. Figure 5.12 shows parallel and lateral presynaptic inhibition. However, recurrent presynaptic inhibition at the level of the spinal cord (similar to recurrent postsynaptic inhibition) could not be detected in mammals, although in frogs

it has been revealed.

In reality, the relationship between excitatory and inhibitory neurons is much more complex than shown in Fig. 5.11 and 5.12, nevertheless, all variants of pre- and postsynaptic inhibition can be combined into two groups: 1) when one’s own path is blocked by the spreading excitation itself with the help of intercalary inhibitory cells (parallel and recurrent inhibition) and 2) when other nerve elements are blocked under the influence of impulses from neighboring excitatory neurons with the inclusion of inhibitory cells (lateral and direct inhibition). Since inhibitory cells themselves can be inhibited by other inhibitory neurons (inhibition of inhibition), this can facilitate the spread of excitation.

IN. The role of inhibition.

1. Both known types of inhibition, with all their varieties, play a protective role. The absence of inhibition would lead to the depletion of transmitters in the axons of neurons and the cessation of central nervous system activity.

2. Inhibition plays an important role in processing information entering the central nervous system. This role is especially pronounced in pre-synaptic inhibition. It regulates the excitation process more precisely, since individual nerve fibers can be blocked by this inhibition. Hundreds and thousands of impulses can approach one excitatory neuron at different terminals. At the same time, the number of impulses reaching the neuron is determined by presynaptic inhibition. Inhibition of lateral pathways ensures the selection of significant signals from the background. Blockade of inhibition leads to widespread irradiation of excitation and convulsions (for example, when presynaptic inhibition by bicuculline is turned off).

3. Inhibition is an important factor in ensuring the coordination activity of the central nervous system.

Each cell, system and internal organ is a single whole; to ensure the interaction and coordinated work of all organs, a central nervous system is necessary. This element of the body is represented in the form of structural and functional units and processes branching from them of various lengths and purposes.

The central nervous system is formed from several components - the brain and spinal cord, interacting through the peripheral nervous system. The human central nervous system is responsible for the following feelings and sensations:

• organs of hearing and vision, perception of sounds and light, response to external stimuli;
• smell and touch, with the help of which the external world and the environment are perceived;
• emotionality, sensitivity;
• memory and thought processes of the body, intellectual activity.

The brain structure of the central nervous system consists of gray and white matter. The gray substance is represented by nerve cells with small branching processes. This substance occupies the center of the spinal cord, affecting the spinal canal. In the brain, the gray matter is the main component of the cortex, having scattered formations that are essentially white. The white layer is located under the gray layer and is structurally formed from fibers involved in the formation of nerve bundles. Similar bundles of bundles build the nerve.

Shells of the central nervous system

Surrounding the central NS are shells, each of which is different:

1. Solid - external. It is this membrane that is formed inside the cranial cavity, as well as inside the hollow formation of the spinal column.
2. Cobweb cover. This membrane is equipped with nerve endings and blood vessels and is located under the outer membrane.
3. Vascular. Between the second and third membranes there is another cavity, the space of which is filled with brain matter. The choroid, as the name suggests, is formed from a collection of arteries, capillaries, and veins that perform the functions of blood vessels. This cover is connected directly to the brain, penetrating its folds.

Brain

This organ has a simple structure and is represented by the following elements: an extended formation - the trunk, a small brain called the cerebellum, which is responsible for muscle tone, coordination and balance, as well as the cerebral hemispheres.

The main element, which includes the higher centers representing reason, mental abilities, and speech abilities, is the hemispheres of the brain. Each of them is formed from a core with gray matter, a white shell and a cerebral cortex that protects the remaining layers.

The cerebellum, which provides coordinated actions, is represented by gray matter, a shell of white matter, and a layer of gray located outside.

The trunk is a part that has no division into layers, is formed from one mass that is not divided into colors. This part directly communicates with the rest and corrects the work of breathing, circulatory systems, movement and feelings.

Spinal cord

This cylindrical organ is located in the depths of the spinal column and has protection in the form of bone tissue formation. The spinal cord itself is located under the membranes.

If you look at the organ in section, you can see gray matter in the form of a butterfly or shaped like an H, covered with a white membrane on top. Some of the pathways originate in white matter and end in gray matter and vice versa. Many fibers located in the white mass of the shell organize the interaction of many parts of the gray matter located in the spinal cord.

Functionality of the central nervous system

The structure of any individual is represented by many structures and organs that interact with each other, but all of them are aimed at promoting the normal functioning of the human structure, its protection, support, and nutrition. The interconnection between the systems is ensured by the central nervous system. It is she who regulates the processes that occur in the body; with its help, the direction of work is changed, the pace of functioning is set and all the necessary conditions are provided for this.

The central nervous system performs a number of basic functions without which the body cannot exist:

1. Integration. Occurs by combining functions. Integration is divided into 3 forms:

• nervous - a combination of departments of the central nervous system. For example, let's take food that has color and aroma, which is a conditioned reflex stimulus. Various reflexes occur in the body at the sight of food: saliva is secreted, gastric juice is produced. In this particular case, one can observe the integration of behavioral, nutritional and bodily prescriptions;
• humoral. It is a combination of various functions based on body fluids together with hormones. For example, various hormones of internal secretions tend to act synchronously, only increasing the effect of each other, but there is a variant of sequential production, when one hormone increases the effect of another. The process ends with the activation of a number of different functions. So, adrenaline can increase heart rate, increase blood glucose levels, start ventilation, etc.;
• mechanical. This shape is necessary to perform a specific function that ensures the structural integrity of the organ. If any of the organs or parts of the body is injured, structural changes are formed, which subsequently leads to a malfunction of the entire organism.

1. Correlation. It is necessary in order to most effectively form the relationship between systems, internal organs and processes, and bring them together.
2. Regulation. Ensuring the functioning of the entire central nervous system, it is necessary to regulate and monitor the main indicators of the body. The basis of this regulation is reflexes, the formation and organization of processes, self-regulation, thanks to which the body adapts to the constantly changing internal conditions of the surrounding world. It occurs in forms that are corrective as the action progresses, and are nourishing. The nerve processes related to the body and stimulation have all sorts of effects.
3. Coordination. Synchronization and consistency of actions of all parts of one unified system. Change of position or posture, various forms of movement, movement in space, adaptation of reactions to what is happening, work activity, physical activity - all these components must be clearly coordinated and directed by the central nervous system.
4. Connection with the environment. The central nervous system is a center that forms the connection and transmission of data from the outside world to the organs and systems of the body for subsequent coordinated actions.
5. Cognition and adaptation. In order to adapt to certain circumstances, to select the model of behavior needed at that moment in special situations, to adapt to the activity, this function of the central nervous system is necessary. With the help of this system, comfortable adaptation to the circumstances surrounding a person is ensured.

Possible problems

Damage and disruptions in the functioning of the central nervous system are not uncommon, and therefore can arise for various reasons:

• genetic predisposition, congenital defects and disorders;
• injuries or mechanical damage;
• inflammatory processes;
• viral infections;
• tumor formations, oncology;
• circulatory disorders, vascular pathologies, etc.

Often these pathological changes appear in the womb, because the fetus can be affected by many negative factors:

• infectious diseases of a woman during pregnancy that were not fully treated or not detected in time;
• injuries, incl. during difficult childbirth;
• radioactive exposure;
• toxic effects, intoxication;
• exposure to alcohol or drugs.

Heredity is fraught with the greatest danger; it is especially important to take care of pregnancy in the first months of pregnancy, because it is during this period that the female body is subject to changes and forms the child’s nervous system. The fetus may develop hydrocephalus or microcephaly, which can have dangerous consequences and require lengthy and expensive treatment in the future. They can also make a child disabled for life.

The structure of the central nervous system has many complexities and parts responsible for its operation. Therefore, any even minor deviations from the norm can serve as an obstacle to the full functioning of the whole organism. That is why it is necessary to listen to your body, promptly recognize its danger signals, and eliminate problems and malfunctions in the operation and interaction of individual parts.

It is important to plan your day correctly, correctly distribute the body’s resources, and allocate time for proper rest and sleep. An important role is played by the diet, which should be balanced and natural. Breathe fresh air every day and perform simple physical exercises that will help keep your body in shape and your body in harmony.

The nervous system regulates the activity of all organs and systems, determining their functional unity and ensuring the connection of the body as a whole with the external environment. The structural unit is a nerve cell with processes - a neuron.

Neurons conduct an electrical impulse to each other through bubble formations (synapses) filled with chemical mediators. According to the structure, neurons are of 3 types:

1. sensitive (with many short processes)
2. insertion
3. motor (with long single processes).

The nerve has two physiological properties - excitability and conductivity. The nerve impulse is carried out along separate fibers, isolated on both sides, taking into account the electrical potential difference between the excited area (negative charge) and the non-excited positive one. Under these conditions, the electric current will spread to neighboring areas in jumps without attenuation. The speed of the impulse depends on the diameter of the fiber: the thicker, the faster (up to 120 m/s). Sympathetic fibers conduct the most slowly (0.5-15 m/s) to the internal organs. The transmission of excitation to muscles is carried out through motor nerve fibers that enter the muscle, lose their myelin sheath and branch. They end in synapses with a large number (about 3 million) of vesicles filled with the chemical mediator acetylcholine. There is a synoptic gap between the nerve fiber and the muscle. Nerve impulses arriving at the presynaptic membrane of the nerve fiber destroy the vesicles and release acetylcholine into the synaptic cleft. The mediator reaches the cholinergic receptors of the postsynaptic membrane of the muscle and excitation begins. This leads to an increase in the permeability of the postsynaptic membrane to K + and N a + ions, which rush into the muscle fiber, giving rise to a local current spreading along the muscle fiber. Meanwhile, in the postsynaptic membrane, acetylcholine is destroyed by the enzyme cholinesterase secreted here and the postsynaptic membrane “calms down” and acquires its original charge.

The nervous system is conventionally divided into somatic (arbitrary) and vegetative (automatic) nervous system. The somatic nervous system communicates with the outside world, and the autonomic nervous system maintains vital functions.

In the nervous system there are central– brain and spinal cord and peripheral nervous system - nerves extending from them. Peripheral nerves are motor (with the bodies of motor neurons in the central nervous system), sensory (the bodies of neurons are outside the brain) and mixed.

The Central Nervous System can have 3 types of effects on organs:

Starting (acceleration, braking)

Vasomotor (change in the width of blood vessels)

Trophic (increase or decrease in metabolism)

The response to stimulation from the external system or internal environment is carried out with the participation of the nervous system and is called a reflex. The path along which a nerve impulse travels is called a reflex arc. There are 5 links in it:

1. sensitive center

2. sensitive fiber conducting excitation to the centers

3. nerve center

4. motor fiber to the periphery

5. active organ (muscle or gland)

In any reflex act there are processes of excitation (causes the activity of an organ or strengthens an existing one) and inhibition (weakens, stops the activity or prevents its occurrence). An important factor in the coordination of reflexes in the centers of the nervous system is the subordination of all overlying centers over the underlying reflex centers (the cerebral cortex changes the activity of all body functions). In the central nervous system, under the influence of various reasons, a focus of increased excitability arises, which has the property of increasing its activity and inhibiting other nerve centers. This phenomenon is called dominant and is influenced by various instincts (hunger, thirst, self-preservation and reproduction). Each reflex has its own localization of the nerve center in the central nervous system. Communication in the central nervous system is also needed. When the nerve center is destroyed, the reflex is absent.

Classification of receptors:

According to biological significance: nutritional, defensive, sexual and orientational (familiarization).

Depending on the working organ of the response: motor, secretory, vascular.

According to the location of the main nerve center: spinal, (for example, urination); bulbar (medulla oblongata) – sneezing, coughing, vomiting; mesencephalic (midbrain) - straightening the body, walking; diencephalic (diencephalon) – thermoregulation; cortical – conditioned (acquired) reflexes.

According to the duration of the reflex: tonic (upright) and phasic.

By complexity: simple (pupil dilation) and complex (digestion).

According to the principle of motor innervation (nervous regulation): somatic, autonomic.

According to the principle of formation: unconditional (congenital) and conditional (acquired).

The following reflexes occur through the brain:

1. Food reflexes: sucking, swallowing, digestive juice secretion

2. Cardiovascular reflexes

3. Protective reflexes: coughing, sneezing, vomiting, tearing, blinking

4. Automatic breathing reflex

5. The vestibular nuclei of posture reflex muscle tone are located

The structure of the nervous system.

Spinal cord.

The spinal cord lies in the spinal canal and is a cord 41-45 cm long, somewhat flattened from front to back. At the top it passes into the brain, and at the bottom it sharpens into the brain case at the level of the II lumbar vertebra, from which the atrophied caudal terminal filament extends.

The back of the brain. Anterior (A) and posterior (B) surfaces of the spinal cord:

1 - bridge, 2 - medulla oblongata, 3 - cervical thickening, 4 - anterior median fissure, 5 - lumbosacral thickening, 6 - posterior median sulcus, 7 - posterior lateral sulcus, 8 - conus medullaris, 9 - terminal (terminal) a thread

Cross section of the spinal cord:

1 - pia mater of the spinal cord, 2 - posterior median sulcus, 3 - posterior intermediate sulcus, 4 - posterior root (sensitive), 5 - posterior lateral sulcus, 6 - terminal zone, 7 - spongy zone, 8 - gelatinous substance, 9 - posterior horn, 10 - lateral horn, 11 - dentate ligament, 12 - anterior horn, 13 - anterior root (motor), 14 - anterior spinal artery, 15 - anterior median fissure

The spinal cord is divided vertically into the right and left sides by the anterior median fissure, and at the back by the posterior median sulcus with two faint longitudinal grooves running side by side. These grooves divide each side into three longitudinal cords: anterior, middle and lateral (shells). At the points where the nerves exit to the upper and lower extremities, the spinal cord has two thickenings. At the beginning of the fetal period, the spinal cord occupies the entire spinal canal, and then does not keep up with the rate of growth of the spine. Thanks to this “ascent” of the spinal cord, the nerve roots extending from it take an oblique direction, and in the lumbar region they run inside the spinal canal parallel to the terminal filum and form a bundle - the cauda equina.

Internal structure of the spinal cord. A cross-section of the brain shows that it consists of gray matter (a collection of nerve cells) and white matter (nerve fibers that gather into pathways). In the center, longitudinally, runs the central canal with cerebrospinal fluid (CSF). Inside there is gray matter, which looks like a butterfly and has anterior, lateral and posterior horns. The anterior horn has a short quadrangular shape and consists of cells of the motor roots of the spinal cord. The dorsal horns are longer and narrower and include cells to which the sensory fibers of the dorsal roots approach. The lateral horn forms a small triangular protrusion and consists of cells of the autonomic part of the nervous system. The gray matter is surrounded by white matter, which is formed by the pathways of longitudinally running nerve fibers. Among them there are 3 main types of paths:

Descending fibers from the brain that give rise to the anterior motor roots.

Ascending fibers to the brain from the posterior sensory roots.

Fibers connecting different parts of the spinal cord.

The spinal cord, through the ascending and descending tracts, carries out the conductor function between the brain and various parts of the spinal cord, and is also a segmental reflex center with receptors and working organs. A certain segmental center in the spinal cord and two nearby lateral segments are involved in the implementation of the reflex.

In addition to the motor centers of skeletal muscles, the spinal cord contains a number of autonomic centers. In the lateral horns of the thoracic and upper segments of the lumbar regions there are centers of the sympathetic nervous system that innervate the heart, blood vessels, gastrointestinal tract, skeletal muscles, sweat glands, and pupil dilation. The sacral region contains parasympathetic centers that innervate the pelvic organs (reflex centers for urination, defecation, erection, ejaculation).

The spinal cord is covered with three membranes: the dura mater covers the outside of the spinal cord and between it and the periosteum of the vertebral valve there is adipose tissue and a venous plexus. Deeper lies a thin sheet of arachnoid membrane. The soft membrane directly surrounds the spinal cord and contains the vessels and nerves that supply it. The subarachnoid space between the pia mater and the arachnoid membrane is filled with cerebrospinal fluid (CSF), which communicates with the cerebrospinal fluid of the brain. On the sides, the dentate ligament secures the brain in its position. The spinal cord is supplied with blood by branches of the vertebral posterior costal and lumbar arteries.

Peripheral nervous system.

From the spinal cord there are 31 pairs of mixed nerves that are formed by the fusion of the anterior and posterior roots: 8 pairs of cervical, 12 pairs of thoracic, 5 pairs of lumbar, 5 pairs of sacral and 1 pair of coccygeal nerves. They have specific segments located in the spinal cord. The spinal nerves arise from the segments with two roots on each side (anterior motor and posterior sensory) and unite into one mixed nerve, thereby forming a segmental pair. At the exit from the intervertebral foramen, each nerve is divided into 4 branches:

Returns to the meninges;

To the node of the sympathetic trunk;

Posterior for the muscles and skin of the neck and back. These include the suboccipital and greater occipital nerves emerging from the cervical region. Sensory fibers of the lumbar and sacral nerves form the superior and middle nerves of the buttock.

The anterior nerves are the most powerful and innervate the anterior surface of the trunk and limbs.

Schematic representation of the spinal nerve plexuses:

1 - brain in the cranial cavity, 2 - cervical plexus, 3 - phrenic nerve, 4 - spinal cord in the spinal canal, 5 - diaphragm. 6 - lumbar plexus, 7 - femoral nerve. 8 - sacral plexus, 9 - muscular branches of the sciatic nerve, 10 - common peroneal nerve, 11 - superficial peroneal nerve, 12 - saphenous nerve of the leg, 13 - deep peroneal nerve, 14 - tibial nerve, 15 - sciatic nerve, 16 - median nerve , 17 - ulnar nerve, 18 - radial nerve, 19 - musculocutaneous nerve, 20 - axillary nerve, 21 - brachial plexus

They form 4 plexuses:

Cervical plexus begins with the cervical vertebrae and, at the level of the sternocleidomastoid muscle, is divided into sensory branches (skin, ear, neck and shoulder) and motor nerves that innervate the muscles of the neck; The mixed branch forms the phrenic nerve, which innervates the diaphragm (motor) and (sensory).

Brachial plexus formed by the lower cervical and first thoracic nerves. In the axillary fossa below the collarbone, short nerves begin that innervate the muscles of the shoulder girdle, and long branches of the shoulder girdle under the collarbone innervate the arm.

Medial cutaneous nerve of the shoulder

The medial cutaneous nerve of the forearm innervates the skin of the corresponding areas of the arm.

The musculocutaneous nerve innervates the shoulder flexor muscles, as well as the sensory branch of the skin of the forearm.

The radial nerve innervates the skin and muscles of the posterior surface of the shoulder and forearm, as well as the skin of the thumb, index and middle fingers.

The median nerve gives branches to almost all flexors of the forearm and thumb, and also innervates the skin of the fingers, except the little finger.

The ulnar nerve innervates part of the muscles of the inner surface of the forearm, as well as the skin of the palm, ring and middle fingers, and the flexor muscles of the thumb.

Anterior branches of the thoracic spinal nerves do not form plexuses, but independently form intercostal nerves and innervate the muscles and skin of the chest and anterior abdominal wall.

Lumbar plexus formed by lumbar segments. Three short branches innervate the lower parts of the muscles and skin of the abdomen, external genitalia and upper thigh.

Long branches extend to the lower limb.

The lateral cutaneous nerve of the thigh innervates its outer surface.

The obturator nerve at the hip joint gives branches to the adductor muscles of the thigh and the skin of the inner surface of the thigh.

The femoral nerve innervates the muscles and skin of the anterior thigh, and its cutaneous branch, the saphenous nerve, goes to the medial surface of the leg and dorsum of the foot.

Sacral plexus formed by the lower lumbar, sacral and coccygeal nerves. Coming from the sciatic foramen, it gives short branches to the muscles and skin of the perineum, pelvic muscles and long branches of the leg.

Posterior femoral cutaneous nerve for the gluteal region and posterior thigh.

* The sciatic nerve in the popliteal fossa is divided into the tibial and peroneal nerves, which branch to form the motor nerves of the leg and foot, and also form the calf nerve from the plexus of cutaneous branches.

Brain.

The brain is located in the cranial cavity. Its upper part is convex and covered with convolutions of the two cerebral hemispheres, separated by a longitudinal fissure. The base of the brain is flattened and connects to the brainstem and cerebellum, as well as the 12 pairs of cranial nerves.

Base of the brain and exit points of the cranial nerve roots:

1 - olfactory bulb, 2 - olfactory tract, 3 - anterior perforated substance, 4 - gray tubercle, 5 - optic tract, 6 - mastoid bodies, 7 - trigeminal ganglion, 8 - posterior perforated space, 9 - pons, 10 - cerebellum, 11 - pyramid, 12 - olive, 13 - spinal nerve, 14 - hypoglossal nerve, 15 - accessory nerve, 16 - vagus nerve, 17 - lysopharyngeal nerve, 18 - vestibulocochlear nerve, 19 - facial nerve, 20 - abducens nerve, 21 - trigeminal nerve, 22 - trochlear nerve, 23 - oculomotor nerve, 24 - optic nerve, 25 - olfactory sulcus

The brain grows until the age of 20 and gains different weight, on average 1245g in women, 1375g in men. The brain is covered with the same membranes as the spinal cord: the dura mater forms the periosteum of the skull, in some places it splits into two layers and forms sinuses with venous blood. Dura shell forms many processes that extend between the processes of the brain: the falx cerebellum enters the longitudinal fissure between the hemispheres, the falx cerebellum separates the cerebellar hemispheres. The tent separates the cerebellum from the hemispheres, and the sella turcica of the sphenoid bone with the underlying pituitary gland is closed by the sella diaphragm.

Sinuses of the dura mater:

1 - cavernous sinus, 2 - inferior petrosal sinus, 3 - superior petrosal sinus, 4 - sigmoid sinus, 5 - transverse sinus. 6 - occipital sinus, 7 - superior sagittal sinus, 8 - straight sinus, 9 - inferior sagittal sinus

Arachnoid– transparent and thin lies on the brain. In the area of ​​the recesses of the brain, expanded areas of the subarachnoid space - cisterns - are formed. The largest cisterns are located between the cerebellum and medulla oblongata, as well as at the base of the brain. Soft shell contains vessels and directly covers the brain, entering all the cracks and grooves. Cerebrospinal fluid (CSF) is formed in the choroid plexuses of the ventricles (intracerebral cavities). It circulates inside the brain through the ventricles, outside in the subarachnoid space and descends into the central canal of the spinal cord, providing constant intracranial pressure, protection and metabolism in the central nervous system.

Projection of the ventricles onto the surface of the cerebrum:

1 - frontal lobe, 2 - central sulcus, 3 - lateral ventricle, 4 - occipital lobe, 5 - posterior horn of the lateral ventricle, 6 - IV ventricle, 7 - cerebral aqueduct, 8 - III ventricle, 9 - central part of the lateral ventricle, 10 - lower horn of the lateral ventricle, 11 - anterior horn of the lateral ventricle.

The brain is supplied with blood by the vertebral and carotid arteries, which form the anterior, middle and posterior cerebral arteries, connected at the base by the arterial (Vesilian) circle. The superficial veins of the brain directly flow into the venous sinuses of the dura mater, and the deep veins collect in the 3rd ventricle into the most powerful vein of the brain (Galen), which flows into the direct sinus of the dura mater.

Arteries of the brain. Bottom view (from R. D. Sinelnikov):

1 - anterior communicating artery. 2 - anterior cerebral arteries, 3 - internal carotid artery, 4 - middle cerebral artery, 5 - posterior communicating artery, 6 - posterior cerebral artery, 7 - basilar artery, 8 - vertebral artery, 9 - posterior inferior cerebellar artery. 10 - anterior inferior cerebellar artery, 11 - superior cerebellar artery.

The brain consists of 5 parts, which are divided into the main evolutionarily ancient structures: medulla oblongata, hindbrain, middle, intermediate, and also into an evolutionarily new structure: the telencephalon.

Medulla connects to the spinal cord at the point where the first spinal nerves exit. On its front surface two longitudinal pyramids and oblong olive trees lying on top outside of them are visible. Behind these formations the structure of the spinal cord continues, which passes to the lower cerebellar peduncles. The medulla oblongata contains the nuclei of the IX - XII pairs of cranial nerves. The medulla oblongata provides a conductive connection between the spinal cord and all parts of the brain. The white matter of the brain is formed by long systems of conducting fibers to and from the spinal cord, as well as short pathways to the brain stem.

The hindbrain is represented by the pons and cerebellum.

Bridge below it borders with the medulla oblongata, above it passes into the cerebral peduncles, and laterally into the middle peduncles of the cerebellum. In front are their own accumulations of gray matter, and behind them are the olivary nuclei and reticular formation. The nuclei of nerves V - VIII also lie here. The white matter of the pons is represented in front by transverse fibers going to the cerebellum, and in the back by ascending and descending fiber systems.

Cerebellum is located opposite. It consists of two hemispheres with narrow convolutions of the cortex with gray matter and a central part - the vermis, in the depths of which the cerebellar nuclei are formed from accumulations of gray matter. From above, the cerebellum passes into the upper peduncles to the midbrain, the middle ones connect to the pons, and the lower ones to the medulla oblongata. The cerebellum is involved in the regulation of movements, making them smooth, precise and is an assistant to the cerebral cortex in controlling skeletal muscles and the activity of autonomic organs.

Fourth ventricle is the cavity of the medulla oblongata and hindbrain, which communicates from below with the central spinal canal, and from above passes into the cerebral aqueduct of the midbrain.

Midbrain consists of the cerebral peduncles and the roof plate with two upper hills of the visual pathway and two lower hills of the auditory pathway. From them originates the motor pathway going to the anterior horns of the spinal cord. The cavity of the midbrain is the cerebral aqueduct, which is surrounded by gray matter with nuclei of the III and IV pairs of the brain. nerves. Inside, the midbrain has three layers: a roof, a tegmentum with systems of ascending pathways and two large nuclei (red and nuclei of the reticular formation), as well as the cerebral peduncles (or base of the formation). The black substance lies on top of the base, and below the base is formed by fibers of the pyramidal tracts and tracts connecting the cerebral cortex with the pons and cerebellum. The midbrain plays an important role in regulating muscle tone and in standing and walking. Nerve fibers from the cerebellum, basal ganglia and cerebral cortex approach the red nuclei, and from them motor impulses are sent along the extrapyramidal tract originating here to the spinal cord. The sensory nuclei of the quadrigeminal region perform primary auditory and visual reflexes (accommodation).

Diencephalon fuses with the cerebral hemispheres and has four formations and the cavity of the third ventricle in the middle, which communicates in front with the 2 lateral ventricles, and in the back passes into the cerebral aqueduct. The thalamus is represented by paired clusters of gray matter with three groups of nuclei to integrate processing and switching of all sensory pathways (except olfactory). Plays a significant role in emotional behavior. The upper layer of the white matter of the thalamus is connected with all the motor nuclei of the subcortex - the basal nuclei of the cerebral cortex, the hypothalamus and the nuclei of the midbrain and medulla oblongata.

The thalamus and other parts of the brain in a midline longitudinal section of the brain:

1 - hypothalamus, 2 - cavity of the third ventricle, 3 - anterior (white) commissure, 4 - cerebral fornix, 5 - corpus callosum, 6 - interthalamic fusion. 7 - thalamus, 8 - epithalamus, 9 - midbrain, 10 - pons, 11 - cerebellum, 12 - medulla oblongata.

In the epithalamus lies the upper appendage of the brain, the epiphysis (pineal body) on two leashes. The metathalamus is connected by bundles of fibers to the plate of the roof of the midbrain, which contain nuclei that are reflex centers of vision and hearing. The hypothalamus includes the subtubercular region itself and a number of formations with neurons capable of secreting neurosecretion, which then enters the lower appendage of the brain - the pituitary gland. The hypothalamus regulates all autonomic functions, as well as metabolism. The parasympathetic centers are located in the anterior sections, and the sympathetic centers in the posterior sections. The hypothalamus has centers that regulate body temperature, thirst and hunger, fear, pleasure and non-pleasure. From the anterior hypothalamus, the hormones vagopressin and oxytocin flow down the long processes of neurons (axons) into the storage system of the posterior anterior lobe of the pituitary gland to enter the blood. And from the posterior section, releasing factor substances enter the pituitary lobe through the blood vessels, stimulating the formation of hormones in its anterior lobe.

Reticular formation.

The reticular (reticular) formation consists of nerve cells of the brain itself and their fibers, with an accumulation of neurons in the core of the reticular formation. This is a dense network of branching processes of neurons of specific nuclei of the brain stem (medulla oblongata, midbrain and diencephalon), conducting certain types of sensitivity from receptors from the periphery to the brain stem and further to the cerebral cortex. In addition, nonspecific pathways to the cerebral cortex, subcortical nuclei and spinal cord begin from the neurons of the reticular formation. Without its own territory, the reticular formation is a regulator of muscle tone, as well as a functional corrector of the brain and spinal cord, providing an activating effect that maintains alertness and concentration. It can be compared to the role of a regulator on a TV: without giving an image, it can change the illumination and sound volume.

Finite brain.

It consists of two separated hemispheres, which are connected by a plate of white matter of the corpus callosum, below which there are two lateral ventricles communicating with each other. The surface of the hemispheres completely repeats the inner surface of the skull, has a complex pattern due to the convolutions and hemispheres between them. The sulci of each hemisphere are divided into 5 lobes: frontal, parietal, temporal, occipital and hidden lobe. The cerebral cortex is covered with gray matter. Up to 4 mm thick. Moreover, on top there are sections of an evolutionarily newer crust of 6 layers, and below it lies a new crust with fewer layers and a simpler structure. The oldest part of the cortex is the rudimentary formation of animals - the olfactory brain. At the point of transition to the lower (basal) surface there is a hippocampal ridge, which participates in the formation of the walls of the lateral ventricles. Inside the hemispheres there are accumulations of gray matter in the form of the basal ganglia. They are subcortical motor centers. White matter occupies the space between the cortex and the basal ganglia. It consists of a large number of fibers, which are divided into 3 categories:

1. Combinative (associative), connecting different parts of one hemisphere.

2. Commissural (commissural), connecting the right and left hemispheres.

3. Projection fibers of the pathways from the hemispheres to the low brain and spinal cord.

Conducting pathways of the brain and spinal cord.

The system of nerve fibers that conduct impulses from various parts of the body to parts of the central nervous system are called ascending (sensitive) pathways, which usually consist of 3 neurons: the first is always located outside the brain, located in the spinal ganglia or sensory ganglia of the cranial nerves. The systems of the first fibers from the cortex and underlying nuclei of the brain through the spinal cord to the working organ are called motor (descending) pathways. They are formed from two neurons, the latter is always represented by cells of the anterior horns of the spinal cord or cells of the motor nuclei of the cranial nerves.

Sensory pathways (ascending) . The spinal cord conducts 4 types of sensitivity: tactile (touch and pressure), temperature, pain and proprioceptive (articular-muscular sense of body position and movement). The bulk of the ascending pathways conduct proprioceptive sensitivity to the cerebral cortex and the cerebellum.

Ecteroceptive pathways:

The lateral spinothalamic tract is the path of pain and temperature sensitivity. The first neurons are located in the spinal ganglia, giving peripheral processes to the spinal nerves and central processes and central processes that go to the dorsal horn of the spinal cord (2nd neuron). At this site, a crossover occurs and then the processes rise along the lateral cord of the spinal cord and further towards the thalamus. The processes of the 3rd neuron in the thalamus form a bundle going to the postcentral gyrus of the cerebral hemispheres. As a result of the fibers crossing along the way, impulses from the left side of the body are transmitted to the right hemisphere and vice versa.

The anterior spinothalamic tract is the pathway of touch and pressure. It consists of fibers that conduct tactile sensitivity, which pass in the anterior cord of the spinal cord.

Proprioceptive pathways:

The posterior spinocerebellar tract (Flexiga) starts from the neuron of the spinal ganglion (1 neuron) with a peripheral process going to the musculo-articular apparatus, and the central process goes as part of the dorsal root to the dorsal horn of the spinal cord (2nd neuron). The processes of the second neurons rise along the lateral cord of the same side to the cells of the cerebellar vermis.

The fibers of the anterior spinocerebellar tract (Govers) form a decussation twice in the spinal cord and before entering the cerebellar vermis in the midbrain region.

The proprioceptive pathway to the cerebral cortex is represented by two bundles: a gentle bundle from the proprioceptors of the lower extremities and the lower half of the body and lies in the posterior cord of the spinal cord. The wedge-shaped bundle is adjacent to it and carries impulses from the upper half of the body and arms. The second neuron lies in the nuclei of the same name in the medulla oblongata, where they intersect and gather into a bundle and reaches the thalamus (3rd neuron). The processes of the third neurons are directed to the sensitive and partial motor zone of the cortex.

Motor tracts (descending).

Pyramid paths:

Cortical-nuclear pathway- control of conscious head movements. It starts from the precentral gyrus and moves to the motor roots of the cranial nerves on the opposite side.

Lateral and anterior corticospinal tracts- begin in the precentral gyrus and, after decussation, go to the opposite side to the motor roots of the spinal nerves. They control conscious movements of the muscles of the trunk and limbs.

Reflex (extrapyramidal) pathway. It includes the red nuclear spinal cord, which begins and decussates in the midbrain and goes to the motor roots of the anterior horns of the spinal cord; they form the maintenance of skeletal muscle tone and control automatic habitual movements.

Tectospinal tract also begins in the midbrain and is associated with auditory and visual perception. It establishes a connection between the quadrigeminal cord and the spinal cord; it transmits the influence of the subcortical centers of vision and hearing on the tone of skeletal muscles, and also forms protective reflexes

Vestibulospinal path- from the rhomboid fossa of the wall of the fourth ventricle of the medulla oblongata, is associated with maintaining the balance of the body and head in space.

Reticulum-spinal tract begins from the nuclei of the reticular formation, which then diverges both along its own and on the opposite side of the spinal nerves. It transmits impulses from the brain stem to the spinal cord to maintain skeletal muscle tone. Regulates the state of the spinal-brain autonomic centers.

Motor zones cerebral cortex are located in the precentral gyrus, where the size of the zone is proportional not to the mass of the muscles of a body part, but to its accuracy of movements. The area for controlling movements of the hand, tongue and facial muscles is especially large. The path of impulses of derivative movements from the cortex to the motor neurons of the opposite side of the body is called the pyramidal pathway.

Sensitive areas are located in different parts of the cortex: the occipital zone is associated with vision, and the temporal zone with hearing; skin sensitivity is projected in the postcentral zone. The size of individual areas is not the same: the projection of the skin of the hand occupies a larger area in the cortex than the projection of the surface of the body. Articular-muscular sensitivity is projected into the postcentral and precentral gyri. The olfactory zone is located at the base of the brain, and the projection of the taste analyzer is located in the lower part of the postcentral gyrus.

Limbic system consists of formations of the telencephalon (cingulate gyrus, hippocampus, basal ganglia) and has extensive connections with all areas of the brain, reticular formation, and hypothalamus. It provides supreme control of all autonomic functions (cardiovascular, respiratory, digestive, metabolism and energy), and also forms emotions and motivation.

Association zones occupy the remaining surface and communicate between different areas of the cortex, combining all impulses flowing into the cortex into integral acts of learning (reading, writing, speech, logical thinking, memory) and providing the possibility of an adequate response of behavior.

Cranial nerves:

12 pairs of cranial nerves arise from the brain. Unlike the spinal nerves, some of the cranial nerves are motor (III, IV, VI, VI, XI, XII pairs), some are sensory (I, II, VIII pairs), the rest are mixed (V, VII, IX, X). The cranial nerves also contain parasympathetic fibers for smooth muscles and glands (III, VII, IX, X pairs).

I. Pair (olfactory nerve) - represented by processes of olfactory cells, the upper nasal passage, which form the olfactory bulb in the ethmoid bone. From this second neuron, impulses travel along the olfactory tract to the cerebral cortex.

II. Pair (optic nerve) formed by the processes of nerve cells of the retina, then in front of the sella turcica of the sphenoid bone it forms an incomplete chiasm of the optic nerves and passes into two visual tracts heading to the subcortical visual centers of the thalamus and midbrain.

III. Pair (oculomotor) motor with an admixture of parasympathetic fibers, starts from the midbrain, passes through the orbit and innervates five of the six muscles of the eyeball, and also parasympathetically innervates the muscle that constricts the pupil and the ciliary muscle.

IV. Pair (block-shaped) motor, starts from the midbrain and innervates the superior oblique muscle of the eye.

V. Pair (trigeminal nerve) mixed: innervates the skin of the face and mucous membranes, is the main sensory nerve of the head. Motor nerves innervate the masticatory and oral muscles. The nuclei of the trigeminal nerve are located in the bridge, from where two roots emerge (motor and sensory), forming the trigeminal ganglion. The peripheral processes form three branches: the ophthalmic nerve, the maxillary nerve and the mandibular nerve. The first two branches are purely sensory, and the third also includes motor fibers.

VI. Pair (abducens nerve) motor, starts from the bridge and innervates the external, rectus muscle of the eye.

VII. Pair (facial nerve) motor, innervates the facial muscles of the face and neck. It begins in the tegmentum of the bridge along with the intermediate nerve, which innervates the papillae of the tongue and salivary glands. They unite in the internal auditory canal, where the facial nerve gives off the greater petrosal nerve and the chorda tympani.

VIII Pair (vestibular-cochlear nerve) consists of the cochlear part, which conducts the auditory sensations of the inner ear, and the vestibular part of the labyrinth of the ear. Connecting, they enter the pons nuclei at the border with the medulla oblongata.

IX. Pair (glossopharyngeal) contains motor, sensory and parasympathetic fibers. Its nuclei lie in the medulla oblongata. In the area of ​​the jugular foramen, the occipital bone forms two nodes of sensory branches to the back of the tongue and pharynx. Parasympathetic fibers are secretory fibers of the parotid gland, and motor fibers are involved in the innervation of the muscles of the pharynx.

X. Pair (wandering) the longest cranial nerve, mixed, begins in the medulla oblongata and with its branches innervates the respiratory organs, passes through the diaphragm and forms the celiac plexus with branches to the liver, pancreas, kidneys, reaching the descending colon. Parasympathetic fibers innervate the smooth muscles of the internal organs, the heart and glands. Motor fibers innervate the skeletal muscles of the pharynx, soft palate, and larynx.

XI. Pair (additional) begins in the medulla oblongata, innervates the sternocleidomastoid muscle of the neck and trapezius muscle with motor fibers

XII. Pair (sublingual) from the medulla oblongata controls the movement of the tongue muscles.

Autonomic nervous system.

The unified nervous system is conventionally divided into two parts: somatic, innervating only skeletal muscles, and autonomic, innervating the entire body as a whole. Coordination of the motor and autonomic functions of the body is carried out by the limbic system and the frontal lobes of the cerebral cortex. Autonomic nerve fibers emerge from only a few areas of the brain and spinal cord, go as part of somatic nerves and necessarily form autonomic nodes, from which post-nodal sections of the reflex arc extend to the periphery. The autonomic nervous system has three types of effects on all organs: functional (acceleration or deceleration), trophic (metabolism) and vasomotor (humoral regulation and homeostasis)

The autonomic nervous system consists of two divisions: sympathetic and parasympathetic.

Scheme of the structure of the autonomic (autonomic) nervous system. Parasympathetic (A) and sympathetic (B) part:

1 - superior cervical ganglion of the sympathetic nerve, 2 - lateral horn of the spinal cord, 3 - superior cervical cardiac nerve, 4 - thoracic cardiac and pulmonary nerves, 5 - great splanchnic nerve, 6 - celiac plexus, 7 - inferior mesenteric plexus, 8 - superior and lower hypogastric plexuses, 9 - small splanchnic nerve, 10 - lumbar splanchnic nerves, 11 - sacral splanchnic nerves, 12 - sacral parasympathetic nuclei, 13 - pelvic splanchnic nerves, 14 - pelvic (parasympathetic) nodes, 15 - parasympathetic nodes (included in organ plexuses), 16 - vagus nerve, 17 - auricular (parasympathetic) node, 18 - submandibular (parasympathetic) node, 19 - ala palatine (parasympathetic) node, 20 - ciliary (parasympathetic) node, 21 - dorsal nucleus of the vagus nerve, 22 - inferior salivary nucleus, 23 - superior salivary nucleus, 24 - accessory nucleus of the oculomotor nerve. Arrows show the paths of nerve impulses to organs

Sympathetic nervous system . The central section is formed by cells of the lateral horns of the spinal cord at the level of all thoracic and upper three lumbar segments. Sympathetic nerve fibers leave the spinal cord as part of the anterior roots of the spinal nerves and form sympathetic trunks (right and left). Then each nerve, through the white connecting branch, connects to the corresponding node (ganglion). The nerve ganglia are divided into two groups: on the sides of the spine, the paravertebral ganglia with the right and left sympathetic trunk, and the prevertebral ganglia, which lie in the thoracic and abdominal cavities. After the nodes, the postganglionic gray connecting branches go to the spinal nerves, the sympathetic fibers of which form plexuses along the arteries supplying the organ.

The sympathetic trunk has different sections:

Cervical region consists of three nodes with outgoing branches innervating the organs of the head, neck and heart.

Thoracic region consists of 10-12 nodes lying in front of the necks of the ribs and outgoing branches to the aorta, heart, lungs and esophagus, forming organ plexuses. The largest large and small splanchnic nerves pass through the diaphragm into the abdominal cavity to the solar (celiac) plexus with preganglionic fibers of the celiac ganglia.

Lumbar consists of 3-5 nodes with branches forming the plexuses of the abdominal cavity and pelvis.

Sacral section consists of 4 nodes on the anterior surface of the sacrum. Below, the chains of nodes of the right and left sympathetic trunks are connected in one coccygeal node. All these formations are united under the name of the pelvic section of the sympathetic trunks and participate in the formation of the pelvic plexuses.

Parasympathetic nervous system. The central sections are located in the brain, of particular importance are the hypothalamic region and the cerebral cortex, as well as in the sacral segments of the spinal cord. In the midbrain lies the Yakubovich nucleus, the processes enter the oculomotor nerve, which switches at the ciliary ganglion border and innervates the ciliary muscle that constricts the pupil. The superior salivary nucleus lies in the rhomboid fossa; its processes enter the trigeminal and then the facial nerve. They form two nodes on the periphery: the pterygopalatine node, which innervates with its trunks the lacrimal glands and glands of the nasal and oral cavity, and the submandibular node, the submandibular and sublingual and sublingual glands. The inferior salivary nucleus penetrates with its processes into the glossopharyngeal nerve and switches in the ear ganglion and gives rise to the “secretory” fibers of the parotid gland. The largest number of parasympathetic fibers passes through the vagus nerve, starting from the dorsal nucleus and innervating all organs of the neck, chest and abdominal cavity up to and including the transverse colon. Parasympathetic innervation of the descending and colon, as well as all pelvic organs, is carried out by the pelvic nerves of the sacral spinal cord. They participate in the formation of the autonomic nerve plexuses and switch in the plexus nodes of the pelvic organs.

The fibers form plexuses with the sympathetic processes, which enter the internal organs. The fibers of the vagus nerves are switched in nodes located in the walls of organs. In addition, parasympathetic and sympathetic fibers form large mixed plexuses, which consist of many clusters of nodes. The largest plexus of the abdominal cavity is the celiac (solar) plexus, from which the postgantlionar branches form plexuses on the vessels to the organs. Another powerful autonomic plexus descends along the abdominal aorta: the superior hypogastric plexus, which descends into the pelvis to form the right and left hypogastric plexus. Sensitive fibers from internal organs also pass through these plexuses.

Well, aren't your brains swollen? - Yan asked and turned into a teapot with a rattling lid from the steam escaping.

Well, yes, you gave me a hard time - said Yai and scratched the back of his head - although, basically, everything is clear.

Well done!!! “You deserve a medal,” Yan said and hung a shiny circle around Ya’s neck.

Wow! How brilliant and clearly written “To the greatest smart guy of all time.” Well, thank you? And what should I do with her?

And you smell it.

Why does it smell like chocolate? Ah-ah-ah, this is such a candy! Yai said and unfolded the foil.

Eat for now, sweets are good for brain function, and I’ll tell you another interesting thing: you saw this medal, touched it with your hands, smelled it, and now you hear it crunching in your mouth with what parts of the body?

Well, many different things.

So, all of them are called sense organs, which help the body navigate the environment and use it for its needs.

The main functions of the central nervous system, along with the peripheral one, which is part of the general human nervous system, are conductive, reflexive and controlling. The highest department of the central nervous system, the so-called “main center” of the nervous system of vertebrates, is the cerebral cortex - back in the 19th century, the Russian physiologist I. P. Pavlov defined its activity as “higher”.

What makes up the human central nervous system

What parts does the human central nervous system consist of and what are its functions?

The structure of the central nervous system (CNS) includes the brain and spinal cord. In their thickness, areas of gray color (gray matter) are clearly visible, this is the appearance of clusters of neuron bodies, and white matter, formed by the processes of nerve cells, through which they establish connections with each other. The number of neurons of the spinal cord and brain of the central nervous system and the degree of their concentration are much higher in the upper section, which as a result takes the form of a volumetric brain.

Spinal cord of the central nervous system consists of gray and white matter, and in its center there is a canal filled with cerebrospinal fluid.

Brain of the central nervous system consists of several departments. Typically, a distinction is made between the hindbrain (it includes the medulla oblongata, which connects the spinal cord and brain, the pons and the cerebellum), the midbrain and the forebrain, formed by the diencephalon and the cerebral hemispheres.

See what makes up the nervous system in the photos presented on this page.

The back and brain as part of the central nervous system

The structure and functions of parts of the central nervous system: the spinal cord and brain are described here.

The spinal cord looks like a long cord formed by nervous tissue and is located in the spinal canal: from above the spinal cord passes into the medulla oblongata, and below it ends at the level of the 1st-2nd lumbar vertebrae.

Numerous spinal nerves extending from the spinal cord connect it with internal organs and limbs. Its functions as part of the central nervous system are reflex and conduction. The spinal cord connects the brain with the organs of the body, regulates the functioning of internal organs, provides movement of the limbs and torso, and is under the control of the brain.

Thirty-one pairs of spinal nerves emerge from the spinal cord and innervate all parts of the body except the face. All muscles of the limbs and internal organs innervate several spinal nerves, which increases the chances of maintaining function if one of the nerves is damaged.

The cerebral hemispheres are the largest part of the brain. There are right and left hemispheres. They consist of a cortex formed by gray matter, the surface of which is dotted with convolutions and grooves, and processes of nerve cells of white matter. Processes that distinguish humans from animals are associated with the activity of the cerebral cortex: consciousness, memory, thinking, speech, labor activity. Based on the names of the skull bones to which the various parts of the cerebral hemispheres are adjacent, the brain is divided into lobes: frontal, parietal, occipital and temporal.

A very important part of the brain, responsible for the coordination of movements and balance of the body, is cerebellum- located in the occipital part of the brain above the medulla oblongata. Its surface is characterized by the presence of many folds, convolutions and grooves. The cerebellum is divided into a middle part and lateral sections - the cerebellar hemispheres. The cerebellum is connected to all parts of the brain stem.

The brain, which is part of the human central nervous system, controls and directs the functioning of human organs. For example, in the medulla oblongata there are respiratory and vasomotor centers. Rapid orientation during light and sound stimulation is provided by centers located in the midbrain.

Diencephalon participates in the formation of sensations. There are a number of zones in the cerebral cortex: for example, in the musculocutaneous zone, impulses coming from receptors in the skin, muscles, and joint capsules are perceived, and signals are formed that regulate voluntary movements. In the occipital lobe of the cerebral cortex there is a visual zone that perceives visual stimuli. The auditory area is located in the temporal lobe. On the inner surface of the temporal lobe of each hemisphere there are gustatory and olfactory zones. And finally, in the cerebral cortex there are areas that are unique to humans and absent in animals. These are the areas that control speech.

Twelve pairs of cranial nerves emerge from the brain, primarily from the brain stem. Some are only motor nerves, such as the oculomotor nerve, which is responsible for certain eye movements. There are also only sensitive ones, for example, the olfactory and ocular nerves, which are responsible for smell and vision, respectively. Finally, some cranial nerves have a mixed structure, like the facial nerve. The facial nerve controls facial movements and plays a role in the sense of taste. The cranial nerves primarily innervate the head and neck, with the exception of the vagus nerve, which is associated with the parasympathetic nervous system, which regulates the pulse, respiration, and digestive system.

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