CNS (central nervous system), its departments, functions. Anatomy and functions of the central nervous system

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 body’s needs in different conditions his life activity.

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 idea 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 implementation without conditioned 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 internal environment 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. By 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 spinal cord two fast-acting transmitters are installed 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, in the excitation of CNS neurons there are characteristics, the main ones being 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 finds wide application 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, to various substances administered for therapeutic purposes pharmacological drugs. 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 damage 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 main reason 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 one, i.e., dominant in this moment in the central nervous system, nerve center.

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. Successful completion of these behavioral acts ultimately eliminates physiological reasons dominant state of 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 research inhibition in the central nervous system, while 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. Braking is important factor ensuring the coordination activities of the central nervous system.

With the evolutionary complexity of multicellular organisms and the functional specialization of cells, the need arose for the regulation and coordination of life processes at the supracellular, tissue, organ, systemic and organismal levels. These new regulatory mechanisms and systems had to appear along with the preservation and complexity of the mechanisms for regulating the functions of individual cells using signaling molecules. Adaptation of multicellular organisms to changes in the environment could be carried out on the condition that new regulatory mechanisms would be able to provide quick, adequate, targeted responses. These mechanisms must be able to remember and retrieve from the memory apparatus information about previous influences on the body, and also have other properties that ensure effective adaptive activity of the body. They became the mechanisms of the nervous system that appeared in complex, highly organized organisms.

Nervous system is a set of special structures that unites and coordinates the activities of all organs and systems of the body in constant interaction with the external environment.

The central nervous system includes the brain and spinal cord. The brain is divided into the hindbrain (and pons), reticular formation, subcortical nuclei, . The bodies form the gray matter of the central nervous system, and their processes (axons and dendrites) form the white matter.

General characteristics of the nervous system

One of the functions of the nervous system is perception various signals (stimulants) of the external and internal environment of the body. Let us remember that any cells can perceive various signals from their environment with the help of specialized cellular receptors. However, they are not adapted to perceive a number of vital signals and cannot instantly transmit information to other cells, which function as regulators of the body’s holistic adequate reactions to the action of stimuli.

The impact of stimuli is perceived by specialized sensory receptors. Examples of such stimuli can be light quanta, sounds, heat, cold, mechanical influences (gravity, pressure changes, vibration, acceleration, compression, stretching), as well as signals of a complex nature (color, complex sounds, words).

To assess the biological significance of perceived signals and organize an adequate response to them in the receptors of the nervous system, they are converted - coding into a universal form of signals understandable to the nervous system - into nerve impulses, carrying out (transferred) which along nerve fibers and pathways to nerve centers are necessary for their analysis.

Signals and the results of their analysis are used by the nervous system to organizing responses to changes in the external or internal environment, regulation And coordination functions of cells and supracellular structures of the body. Such responses are carried out by effector organs. The most common responses to impacts are motor (motor) reactions of skeletal or smooth muscles, changes in the secretion of epithelial (exocrine, endocrine) cells, initiated by the nervous system. Taking a direct part in the formation of responses to changes in the environment, the nervous system performs the functions regulation of homeostasis, provision functional interaction organs and tissues and their integration into a single integral organism.

Thanks to the nervous system, adequate interaction of the body with the environment is carried out not only through the organization of responses by effector systems, but also through its own mental reactions - emotions, motivation, consciousness, thinking, memory, higher cognitive and creative processes.

The nervous system is divided into central (brain and spinal cord) and peripheral - nerve cells and fibers outside the cavity of the skull and spinal canal. The human brain contains more than 100 billion nerve cells (neurons). Clusters of nerve cells that perform or control the same functions form in the central nervous system nerve centers. The structures of the brain, represented by the bodies of neurons, form the gray matter of the central nervous system, and the processes of these cells, uniting into pathways, form the white matter. In addition, the structural part of the central nervous system are glial cells that form neuroglia. The number of glial cells is approximately 10 times the number of neurons, and these cells make up the majority of the mass of the central nervous system.

The nervous system, according to the characteristics of its functions and structure, is divided into somatic and autonomic (vegetative). The somatic includes the structures of the nervous system, which provide the perception of sensory signals mainly from the external environment through the sensory organs, and control the functioning of the striated (skeletal) muscles. The autonomic (autonomic) nervous system includes structures that ensure the perception of signals primarily from the internal environment of the body, regulate the functioning of the heart, other internal organs, smooth muscles, exocrine and part of the endocrine glands.

In the central nervous system, it is customary to distinguish structures located at different levels, which are characterized by specific functions and roles in the regulation of life processes. Among them are the basal ganglia, brainstem structures, spinal cord, and peripheral nervous system.

Structure of the nervous system

The nervous system is divided into central and peripheral. The central nervous system (CNS) includes the brain and spinal cord, and the peripheral nervous system includes the nerves that extend from the central nervous system to various organs.

Rice. 1. Structure of the nervous system

Rice. 2. Functional division of the nervous system

The meaning of the nervous system:

• unites the organs and systems of the body into a single whole;
• regulates the functioning of all organs and systems of the body;
• communicates the organism with the external environment and adapts it to environmental conditions;
• forms the material basis of mental activity: speech, thinking, social behavior.

Structure of the nervous system

The structural and physiological unit of the nervous system is - (Fig. 3). It consists of a body (soma), processes (dendrites) and an axon. Dendrites are highly branched and form many synapses with other cells, which determines their leading role in the neuron’s perception of information. The axon starts from the cell body with an axon hillock, which is a generator of a nerve impulse, which is then carried along the axon to other cells. The axon membrane at the synapse contains specific receptors that can respond to various mediators or neuromodulators. Therefore, the process of transmitter release by presynaptic endings can be influenced by other neurons. Also, the membrane of the endings contains a large number of calcium channels, through which calcium ions enter the ending when it is excited and activate the release of the mediator.

Rice. 3. Diagram of a neuron (according to I.F. Ivanov): a - structure of a neuron: 7 - body (perikaryon); 2 - core; 3 - dendrites; 4.6 - neurites; 5.8 - myelin sheath; 7- collateral; 9 - node interception; 10 — lemmocyte nucleus; 11 - nerve endings; b — types of nerve cells: I — unipolar; II - multipolar; III - bipolar; 1 - neuritis; 2 -dendrite

Typically, in neurons, the action potential occurs in the region of the axon hillock membrane, the excitability of which is 2 times higher than the excitability of other areas. From here the excitation spreads along the axon and cell body.

Axons, in addition to their function of conducting excitation, serve as channels for the transport of various substances. Proteins and mediators synthesized in the cell body, organelles and other substances can move along the axon to its end. This movement of substances is called axon transport. There are two types of it: fast and slow axonal transport.

Each neuron in the central nervous system performs three physiological roles: it receives nerve impulses from receptors or other neurons; generates its own impulses; conducts excitation to another neuron or organ.

According to their functional significance, neurons are divided into three groups: sensitive (sensory, receptor); intercalary (associative); motor (effector, motor).

In addition to neurons, the central nervous system contains glial cells, occupying half the volume of the brain. Peripheral axons are also surrounded by a sheath of glial cells called lemmocytes (Schwann cells). Neurons and glial cells are separated by intercellular clefts, which communicate with each other and form a fluid-filled intercellular space between neurons and glia. Through these spaces, the exchange of substances between nerve and glial cells occurs.

Neuroglial cells perform many functions: supporting, protective and trophic roles for neurons; maintain a certain concentration of calcium and potassium ions in the intercellular space; destroy neurotransmitters and other biologically active substances.

Functions of the central nervous system

The central nervous system performs several functions.

Integrative: The organism of animals and humans is a complex, highly organized system consisting of functionally interconnected cells, tissues, organs and their systems. This relationship, the unification of the various components of the body into a single whole (integration), their coordinated functioning is ensured by the central nervous system.

Coordinating: the functions of various organs and systems of the body must proceed in harmony, since only with this method of life is it possible to maintain the constancy of the internal environment, as well as to successfully adapt to changing environmental conditions. The central nervous system coordinates the activities of the elements that make up the body.

Regulating: The central nervous system regulates all processes occurring in the body, therefore, with its participation, the most adequate changes in the work of various organs occur, aimed at ensuring one or another of its activities.

Trophic: the central nervous system regulates trophism, intensity metabolic processes in the tissues of the body, which underlies the formation of reactions adequate to the changes occurring in the internal and external environment.

Adaptive: The central nervous system communicates the body with the external environment by analyzing and synthesizing various information received from sensory systems. This makes it possible to restructure the activities of various organs and systems in accordance with changes in the environment. It functions as a regulator of behavior necessary in specific conditions of existence. This ensures adequate adaptation to the surrounding world.

Formation of non-directional behavior: the central nervous system forms a certain behavior of the animal in accordance with the dominant need.

Reflex regulation of nervous activity

The adaptation of the vital processes of the body, its systems, organs, tissues to changing environmental conditions is called regulation. Regulation provided jointly by the nervous and hormonal systems is called neurohormonal regulation. Thanks to the nervous system, the body carries out its activities according to the principle of reflex.

The main mechanism of activity of the central nervous system is the body’s response to the actions of a stimulus, carried out with the participation of the central nervous system and aimed at achieving a useful result.

Reflex translated from Latin language means "reflection". The term “reflex” was first proposed by the Czech researcher I.G. Prokhaska, who developed the doctrine of reflective actions. The further development of reflex theory is associated with the name of I.M. Sechenov. He believed that everything unconscious and conscious occurs as a reflex. But at that time there were no methods for objectively assessing brain activity that could confirm this assumption. Later, an objective method for assessing brain activity was developed by Academician I.P. Pavlov, and it was called the method of conditioned reflexes. Using this method, the scientist proved that the basis of the higher nervous activity of animals and humans are conditioned reflexes, formed on the basis of unconditioned reflexes due to the formation of temporary connections. Academician P.K. Anokhin showed that all the diversity of animal and human activities is carried out on the basis of the concept of functional systems.

The morphological basis of the reflex is , consisting of several nerve structures that ensure the implementation of the reflex.

Three types of neurons are involved in the formation of a reflex arc: receptor (sensitive), intermediate (intercalary), motor (effector) (Fig. 6.2). They are combined into neural circuits.

Rice. 4. Scheme of regulation based on the reflex principle. Reflex arc: 1 - receptor; 2 - afferent pathway; 3 - nerve center; 4 - efferent pathway; 5 - working organ (any organ of the body); MN - motor neuron; M - muscle; CN - command neuron; SN - sensory neuron, ModN - modulatory neuron

The dendrite of the receptor neuron contacts the receptor, its axon goes to the central nervous system and interacts with the interneuron. From the interneuron, the axon goes to the effector neuron, and its axon goes to the periphery to the executive organ. This is how it is formed reflex arc.

Receptor neurons are located in the periphery and in the internal organs, while intercalary and motor neurons are located in the central nervous system.

There are five links in the reflex arc: receptor, afferent (or centripetal) path, nerve center, efferent (or centrifugal) path and working organ (or effector).

A receptor is a specialized formation that perceives irritation. The receptor consists of specialized highly sensitive cells.

The afferent link of the arc is a receptor neuron and conducts excitation from the receptor to the nerve center.

The nerve center is formed by a large number of intercalary and motor neurons.

This link of the reflex arc consists of a set of neurons located in various departments CNS. The nerve center receives impulses from receptors along the afferent pathway, analyzes and synthesizes this information, then transmits the formed program of actions along the efferent fibers to the peripheral executive organ. And the working organ carries out its characteristic activity (the muscle contracts, the gland secretes secretions, etc.).

A special link of reverse afferentation perceives the parameters of the action performed by the working organ and transmits this information to the nerve center. The nerve center is an acceptor of the action of the reverse afferentation link and receives information from the working organ about the completed action.

The time from the beginning of the action of the stimulus on the receptor until the appearance of the response is called the reflex time.

All reflexes in animals and humans are divided into unconditioned and conditioned.

Unconditioned reflexes - congenital, hereditary reactions. Unconditioned reflexes are carried out through reflex arcs already formed in the body. Unconditioned reflexes are species specific, i.e. characteristic of all animals of this species. They are constant throughout life and arise in response to adequate stimulation of receptors. Unconditioned reflexes are classified according to biological significance: nutritional, defensive, sexual, locomotor, orientation. Based on the location of the receptors, these reflexes are divided into exteroceptive (temperature, tactile, visual, auditory, taste, etc.), interoceptive (vascular, cardiac, gastric, intestinal, etc.) and proprioceptive (muscle, tendon, etc.). Based on the nature of the response - motor, secretory, etc. Based on the location of the nerve centers through which the reflex is carried out - spinal, bulbar, mesencephalic.

Conditioned reflexes - reflexes acquired by an organism during its individual life. Conditioned reflexes are carried out through newly formed reflex arcs on the basis of reflex arcs of unconditioned reflexes with the formation of a temporary connection between them in the cerebral cortex.

Reflexes in the body are carried out with the participation of endocrine glands and hormones.

The basis of modern ideas about reflex activity The organism has the concept of a useful adaptive result, to achieve which any reflex is performed. Information about the achievement of a useful adaptive result enters the central nervous system via a feedback link in the form of reverse afferentation, which is an obligatory component of reflex activity. The principle of reverse afferentation in reflex activity was developed by P.K. Anokhin and is based on the fact that the structural basis of the reflex is not a reflex arc, but a reflex ring, which includes the following links: receptor, afferent nerve pathway, nerve center, efferent nerve pathway, working organ , reverse afferentation.

When any link of the reflex ring is turned off, the reflex disappears. Therefore, for the reflex to occur, the integrity of all links is necessary.

Properties of nerve centers

Nerve centers have a number of characteristic functional properties.

Excitation in nerve centers spreads unilaterally from the receptor to the effector, which is associated with the ability to conduct excitation only from the presynaptic membrane to the postsynaptic one.

Excitation in nerve centers is carried out more slowly than along a nerve fiber, as a result of a slowdown in the conduction of excitation through synapses.

A summation of excitations can occur in nerve centers.

There are two main methods of summation: temporal and spatial. At temporal summation several excitation impulses arrive at a neuron through one synapse, are summed up and generate an action potential in it, and spatial summation manifests itself when impulses arrive to one neuron through different synapses.

In them there is a transformation of the rhythm of excitation, i.e. a decrease or increase in the number of excitation impulses leaving the nerve center compared to the number of impulses arriving at it.

Nerve centers are very sensitive to lack of oxygen and the action of various chemicals.

Nerve centers, unlike nerve fibers, are capable of rapid fatigue. Synaptic fatigue with prolonged activation of the center is expressed in a decrease in the number of postsynaptic potentials. This is due to the consumption of the mediator and the accumulation of metabolites that acidify the environment.

The nerve centers are in a state of constant tone, due to the continuous receipt of a certain number of impulses from the receptors.

Nerve centers are characterized by plasticity—the ability to increase their functionality. This property may be due to synaptic facilitation—improved conduction at synapses after brief stimulation of afferent pathways. With frequent use of synapses, the synthesis of receptors and transmitters is accelerated.

Along with excitation, inhibition processes occur in the nerve center.

Coordination activity of the central nervous system and its principles

One of the important functions of the central nervous system is the coordination function, which is also called coordination activities CNS. It is understood as the regulation of the distribution of excitation and inhibition in neural structures, as well as the interaction between nerve centers that ensure the effective implementation of reflex and voluntary reactions.

An example of the coordination activity of the central nervous system can be the reciprocal relationship between the centers of breathing and swallowing, when during swallowing the breathing center is inhibited, the epiglottis closes the entrance to the larynx and prevents food or liquid from entering the respiratory tract. The coordination function of the central nervous system is fundamentally important for the implementation of complex movements carried out with the participation of many muscles. Examples of such movements include articulation of speech, the act of swallowing, and gymnastic movements that require the coordinated contraction and relaxation of many muscles.

Principles of coordination activities

• Reciprocity - mutual inhibition of antagonistic groups of neurons (flexor and extensor motor neurons)
• Final neuron - activation of an efferent neuron from various receptive fields and competition between various afferent impulses for a given motor neuron
• Switching is the process of transferring activity from one nerve center to the antagonist nerve center
• Induction - change from excitation to inhibition or vice versa
• Feedback is a mechanism that ensures the need for signaling from the receptors of the executive organs for the successful implementation of a function
• A dominant is a persistent dominant focus of excitation in the central nervous system, subordinating the functions of other nerve centers.

The coordination activity of the central nervous system is based on a number of principles.

The principle of convergence is realized in convergent chains of neurons, in which the axons of a number of others converge or converge on one of them (usually the efferent one). Convergence ensures that the same neuron receives signals from different nerve centers or receptors of different modalities (different sensory organs). Based on convergence, a variety of stimuli can cause the same type of response. For example, the guard reflex (turning the eyes and head - alertness) can be caused by light, sound, and tactile influence.

The principle of a common final path follows from the principle of convergence and is close in essence. It is understood as the possibility of carrying out the same reaction, triggered by the final efferent neuron in the hierarchical nerve chain, to which the axons of many other nerve cells converge. An example of a classic terminal pathway is the motor neurons of the anterior horn of the spinal cord or motor nuclei cranial nerves, which directly innervate muscles with their axons. The same motor reaction (for example, bending an arm) can be triggered by the receipt of impulses to these neurons from pyramidal neurons of the primary motor cortex, neurons of a number of motor centers of the brain stem, interneurons of the spinal cord, axons of sensory neurons of the spinal ganglia in response to the action of signals perceived different organs senses (light, sound, gravitational, pain or mechanical effects).

Divergence principle is realized in divergent chains of neurons, in which one of the neurons has a branching axon, and each of the branches forms a synapse with another nerve cell. These circuits perform the functions of simultaneously transmitting signals from one neuron to many other neurons. Thanks to divergent connections, signals are widely distributed (irradiated) and many centers located at different levels of the central nervous system are quickly involved in the response.

The principle of feedback (reverse afferentation) lies in the possibility of transmitting information about the reaction being performed (for example, about movement from muscle proprioceptors) via afferent fibers back to the nerve center that triggered it. Thanks to feedback, a closed neural chain (circuit) is formed, through which you can control the progress of the reaction, regulate the strength, duration and other parameters of the reaction, if they were not implemented.

The participation of feedback can be considered using the example of the implementation of the flexion reflex caused by mechanical impact to skin receptors (Fig. 5). With a reflex contraction of the flexor muscle, the activity of proprioceptors and the frequency of sending nerve impulses along afferent fibers to the a-motoneurons of the spinal cord innervating this muscle change. As a result, a closed regulatory loop is formed, in which the role of a feedback channel is played by afferent fibers, transmitting information about contraction to the nerve centers from muscle receptors, and the role of a direct communication channel is played by efferent fibers of motor neurons going to the muscles. Thus, the nerve center (its motor neurons) receives information about changes in the state of the muscle caused by the transmission of impulses along motor fibers. Thanks to feedback, a kind of regulatory nerve ring is formed. Therefore, some authors prefer to use the term “reflex ring” instead of the term “reflex arc”.

The presence of feedback is important in the mechanisms of regulation of blood circulation, respiration, body temperature, behavioral and other reactions of the body and is discussed further in the relevant sections.

Rice. 5. Feedback circuit in the neural circuits of the simplest reflexes

The principle of reciprocal relations is realized through interaction between antagonistic nerve centers. For example, between a group of motor neurons that control arm flexion and a group of motor neurons that control arm extension. Thanks to reciprocal relationships, the excitation of neurons of one of the antagonistic centers is accompanied by inhibition of the other. In the given example, the reciprocal relationship between the centers of flexion and extension will be manifested by the fact that during the contraction of the flexor muscles of the arm, an equivalent relaxation of the extensors will occur, and vice versa, which ensures the smoothness of flexion and extension movements of the arm. Reciprocal relationships are realized due to the activation by neurons of the excited center of inhibitory interneurons, the axons of which form inhibitory synapses on the neurons of the antagonistic center.

The principle of dominance is also implemented based on the peculiarities of interaction between nerve centers. The neurons of the dominant, most active center (focus of excitation) have persistently high activity and suppress excitation in other nerve centers, subordinating them to their influence. Moreover, the neurons of the dominant center attract afferent nerve impulses addressed to other centers and increase their activity due to the receipt of these impulses. The dominant center can remain in a state of excitement for a long time without signs of fatigue.

An example of a state caused by the presence of a dominant focus of excitation in the central nervous system is the state after a person has experienced an important event for him, when all his thoughts and actions in one way or another become associated with this event.

Properties of the dominant

• Increased excitability
• Excitation persistence
• Excitation inertia
• Ability to suppress subdominant lesions
• Ability to sum up excitations

The considered principles of coordination can be used, depending on the processes coordinated by the central nervous system, separately or together in various combinations.

central nervous system- this is the brain and spinal cord, and the peripheral - the nerves extending from them and ganglia located outside the skull and spine.

The spinal cord is located in the spinal canal. It looks like a tube about 45 cm long and 1 cm in diameter, extending from the brain, with a cavity - a central canal filled with cerebrospinal fluid.

Cross section 48 shows that the spinal cord consists of white (outside) and gray (inside) matter. The gray matter consists of the bodies of nerve cells and has the shape of a butterfly in a cross section, from the outstretched “wings” of which two anterior and two posterior horns extend. The anterior horns contain motor neurons that give rise to motor nerves. The dorsal horns include nerve cells to which the sensory fibers of the dorsal roots approach. Connecting with each other, the anterior and posterior roots form 31 pairs of mixed (motor and sensory) spinal nerves. Each pair of nerves innervates a specific muscle group and a corresponding area of ​​skin.

White matter is formed by processes of nerve cells (nerve fibers) united into conducting pathways. Among them are fibers connecting parts of the spinal cord at different levels, motor descending fibers going from the brain to the spinal cord to connect with the cells that give rise to the anterior motor roots, and sensory ascending fibers, which are partly a continuation of the fibers of the dorsal roots, partly processes cells of the spinal cord and ascend to the brain.

The spinal cord performs two important functions: reflex and conductive. The gray matter of the spinal cord closes the reflex pathways of many motor reactions, such as the knee reflex. It manifests itself in the fact that when tapping the tendon of the quadriceps femoris muscle, lower limit The patella causes reflex extension of the leg at the knee joint. This is explained by the fact that when the ligament is struck, the muscle is stretched, excitation occurs in its nerve receptors, which is transmitted through the centripetal neurons to the gray matter of the spinal cord, passes to the centrifugal neurons and through their long processes to the extensor muscles. Two types of neurons are involved in the knee reflex - centripetal and centrifugal. Most spinal cord reflexes also involve interneurons. Sensory nerves from skin receptors, motor apparatus, blood vessels, digestive tract, excretory and genital organs. Centripetal neurons, through interneurons, communicate with centrifugal motor neurons, which innervate all skeletal muscles (with the exception of facial muscles). The spinal cord also contains many centers of autonomic innervation of internal organs.

Conductor function. Centripetal nerve impulses along the spinal cord transmit information to the brain about changes in the external and internal environment of the body. Along descending pathways, impulses from the brain are transmitted to motor neurons, which cause or regulate the activity of executive organs.

The activity of the spinal cord in mammals and humans is subject to the coordinating and activating influences of the overlying parts of the central nervous system. Therefore, reflexes inherent in the spinal cord itself can be studied in “ pure form» only after separation of the spinal cord from the brain, for example in the spinal frog. The first consequence of transection or injury of the spinal cord is spinal shock (impact, shock), which lasts 3-5 minutes in a frog and 7-10 days in a dog. In case of injury or injury that causes a disruption in the connection between the spinal cord and the brain, spinal shock in a person lasts 3-5 months. At this time, all spinal reflexes disappear. When the shock passes, simple spinal reflexes are restored, but the victim remains paralyzed and becomes disabled.

The brain consists of the posterior, middle and forebrain (49).

12 pairs of cranial nerves depart from the brain, of which the visual, auditory and olfactory are sensory nerves that conduct excitation from the receptors of the corresponding sensory organs to the brain. The rest, with the exception of the purely motor nerves innervating the eye muscles, are mixed nerves.

Medulla performs reflex and conductive functions. Eight pairs of cranial nerves emerge from the medulla oblongata and the pons (pairs V to XII). Along sensory nerves medulla receives impulses from receptors of the scalp, mucous membranes of the mouth, nose, eyes, larynx, trachea, as well as from receptors of the cardiovascular and digestive systems, from the organ of hearing and vestibular apparatus. In the medulla oblongata there is a respiratory center that provides the act of inhalation and exhalation. The centers of the medulla oblongata, innervating the respiratory muscles, muscles of the vocal cords, tongue and lips, play an important role in the formation of speech. Through the medulla oblongata, the reflexes of blinking eyelashes, tearing, sneezing, coughing, swallowing, secreting digestive juices, regulating the functioning of the heart and the lumen of blood vessels are carried out. The medulla oblongata also takes part in the regulation of skeletal muscle tone. Through it, the closure of various nerve pathways connecting the centers of the forebrain, cerebellum and diencephalon with the spinal cord is carried out. The functioning of the medulla oblongata is influenced by impulses coming from the cerebral cortex, cerebellum and subcortical nuclei.

Cerebellum located behind the medulla oblongata and has two hemispheres and a middle part. It consists of gray matter located on the outside and white matter on the inside. Numerous neural pathways The cerebellum is connected to all parts of the central nervous system. If the functions of the cerebellum are impaired, there is a drop in muscle tone, unstable movements, trembling of the head, torso and limbs, impaired coordination, smoothness, movements, disorders of autonomic functions - the gastrointestinal tract, of cardio-vascular system and etc.

Midbrain plays an important role in the regulation of muscle tone, in the implementation of positioning reflexes, thanks to which standing and walking are possible, in the manifestation of the orientation reflex.

Diencephalon consists of the visual hillocks (thalamus) and the subthalamic region (hypothalamus). The visual tuberosities regulate the rhythm of cortical activity and participate in the formation of conditioned reflexes, emotions, etc. The subtuberculous region is connected with all parts of the central nervous system and with the endocrine glands. It is a regulator of metabolism and body temperature, the constancy of the internal environment of the body and the functions of the digestive, cardiovascular, genitourinary systems, as well as endocrine glands.

Mesh formation or reticular formation- this is a cluster of neurons, forming a dense network with their processes, located in the deep structures of the medulla oblongata, midbrain and diencephalon (brain stem). All centripetal nerve fibers give off branches in the brainstem into a reticular formation.

The reticular formation has an activating effect on the cerebral cortex, maintaining a state of wakefulness and concentrating attention. Destruction reticular formation causes deep sleep, and its irritation causes awakening. The cerebral cortex regulates the activity of the retinal formation.

Large cerebral hemispheres brain appeared at relatively late stages of the evolutionary development of the animal world (see section “Zoology”).

In an adult, the cerebral hemispheres make up 80% of the brain mass. The cortex, with a thickness of 1.5 to 3 mm, covers the surface of the brain with an area of ​​1450 to 1700 cm2; it contains from 12 to 18 billion neurons located in six layers of nerve cells of different categories lying on top of each other. More than 2/3 of the bark surface is hidden in deep grooves. The white matter, located under the cortex, consists of nerve fibers that connect various areas of the cortex with other parts of the brain and with the spinal cord. In the white matter of the right and left hemispheres, connected by a bridge of nerve fibers, there are accumulations of gray matter - subcortical nuclei, through which excitations are transmitted to and from the cortex. Three main sulci - central, lateral and parieto-occipital - divide each hemisphere into four lobes: frontal, parietal, occipital and temporal. Based on the characteristics of the cellular composition and structure, the cerebral cortex is divided into a number of areas called cortical fields. The functions of individual areas of the cortex are not the same. Each receptor apparatus on the periphery corresponds to an area in the cortex that I. P. Pavlov called the cortical nucleus of the analyzer.

The visual zone is located in the occipital lobe of the cortex. It receives impulses from the retina of the eye and distinguishes visual stimuli. If the occipital lobe of the cortex is damaged, a person cannot distinguish between surrounding objects and loses the ability to navigate with the help of vision. Deafness occurs when the temporal region, where the auditory zone is located, is destroyed. On the inner surface of the temporal lobe of each hemisphere there are gustatory and olfactory zones. The nuclear zone of the motor analyzer is located in the anterior-central and posterior-central areas of the cortex. The skin analyzer area occupies the posterior central region. The largest area is occupied by the cortical representation of the receptors of the hand and thumb hands, vocal apparatus and face, the smallest - representation of the torso, thigh and lower leg.

The cerebral cortex performs the function of a higher analyzer of signals from all receptors of the body and synthesis of responses into a biologically appropriate act. It is the highest organ of coordination of reflex activity and the organ of acquisition and accumulation of individual life experience, the formation of temporary connections - conditioned reflexes.

The human nervous system is a stimulator of work muscular system, which we talked about in. As we already know, muscles are needed to move body parts in space, and we have even studied specifically which muscles are intended for which work. But what powers the muscles? What and how makes them work? This will be discussed in this article, from which you will learn the necessary theoretical minimum for mastering the topic indicated in the title of the article.

First of all, it is worth informing that the nervous system is designed to transmit information and commands to our body. The main functions of the human nervous system are the perception of changes inside the body and the space surrounding it, the interpretation of these changes and the response to them in the form of a certain form (including muscle contraction).

Nervous system– many different nervous structures interacting with each other, providing, along with the endocrine system, coordinated regulation of the work of most of the body’s systems, as well as a response to changing conditions of the external and internal environment. This system combines sensitization, motor activity and the correct functioning of systems such as endocrine, immune and more.

Structure of the nervous system

Excitability, irritability and conductivity are characterized as functions of time, that is, it is a process that occurs from irritation to the appearance of an organ response. The propagation of a nerve impulse in a nerve fiber occurs due to the transition of local foci of excitation to adjacent inactive areas of the nerve fiber. The human nervous system has the property of transforming and generating energies from the external and internal environment and converting them into a nervous process.

Structure of the human nervous system: 1- brachial plexus; 2- musculocutaneous nerve; 3rd radial nerve; 4- median nerve; 5- iliohypogastric nerve; 6-femoral-genital nerve; 7- locking nerve; 8-ulnar nerve; 9 - common peroneal nerve; 10- deep peroneal nerve; 11- superficial nerve; 12- brain; 13- cerebellum; 14- spinal cord; 15- intercostal nerves; 16- hypochondrium nerve; 17 - lumbar plexus; 18-sacral plexus; 19-femoral nerve; 20- genital nerve; 21-sciatic nerve; 22- muscular branches of the femoral nerves; 23- saphenous nerve; 24 tibial nerve

The nervous system functions as a whole with the senses and is controlled by the brain. The largest part of the latter is called the cerebral hemispheres (in the occipital region of the skull there are two smaller hemispheres of the cerebellum). The brain connects to the spinal cord. The right and left cerebral hemispheres are connected to each other by a compact bundle of nerve fibers called the corpus callosum.

Spinal cord- the main nerve trunk of the body - passes through the canal formed by the foramina of the vertebrae and stretches from the brain to the sacral spine. On each side of the spinal cord, nerves extend symmetrically to various parts bodies. The sense of touch is, in general terms, provided by certain nerve fibers, countless endings of which are located in the skin.

Classification of the nervous system

The so-called types of the human nervous system can be represented as follows. The entire integral system is conditionally formed by: the central nervous system - CNS, which includes the brain and spinal cord, and the peripheral nervous system - PNS, which includes numerous nerves extending from the brain and spinal cord. The skin, joints, ligaments, muscles, internal organs and sensory organs send input signals to the central nervous system via PNS neurons. At the same time, outgoing signals from the central nervous system are sent by the peripheral nervous system to the muscles. As visual material, below, the complete human nervous system (diagram) is presented in a logically structured manner.

central nervous system- the basis of the human nervous system, which consists of neurons and their processes. The main and characteristic function of the central nervous system is the implementation of reflective reactions of varying degrees of complexity, called reflexes. The lower and middle parts of the central nervous system - the spinal cord, medulla oblongata, midbrain, diencephalon and cerebellum - control activity individual organs and body systems, realize communication and interaction between them, ensure the integrity of the body and its correct functioning. The highest department of the central nervous system - the cerebral cortex and the nearest subcortical formations - for the most part controls the connection and interaction of the body as an integral structure with the outside world.

Peripheral nervous system- is a conditionally allocated part of the nervous system, which is located outside the brain and spinal cord. Includes the nerves and plexuses of the autonomic nervous system, connecting the central nervous system to the organs of the body. Unlike the central nervous system, the PNS is not protected by bones and can be susceptible to mechanical damage. In turn, the peripheral nervous system itself is divided into somatic and autonomic.

• Somatic nervous system- part of the human nervous system, which is a complex of sensory and motor nerve fibers responsible for excitation of muscles, including skin and joints. It also guides the coordination of body movements and the reception and transmission of external stimuli. This system performs actions that a person controls consciously.
• Autonomic nervous system divided into sympathetic and parasympathetic. The sympathetic nervous system controls the response to danger or stress, and can, among other things, cause an increase in heart rate, increased blood pressure and stimulation of the senses by increasing the level of adrenaline in the blood. The parasympathetic nervous system, in turn, controls the state of rest, and regulates the contraction of the pupils, slowing heart rate, dilation of blood vessels and stimulation of the digestive and genitourinary systems.

Above you can see a logically structured diagram showing the parts of the human nervous system, in order corresponding to the above material.

Structure and functions of neurons

All movements and exercises are controlled by the nervous system. The main structural and functional unit of the nervous system (both central and peripheral) is the neuron. Neurons– these are excitable cells that are capable of generating and transmitting electrical impulses (action potentials).

Structure of a nerve cell: 1- cell body; 2- dendrites; 3- cell nucleus; 4- myelin sheath; 5- axon; 6- axon ending; 7- synaptic thickening

The functional unit of the neuromuscular system is the motor unit, which consists of a motor neuron and the muscle fibers it innervates. Actually, the work of the human nervous system, using the process of muscle innervation as an example, occurs as follows.

The cell membrane of the nerve and muscle fiber is polarized, that is, there is a potential difference across it. The inside of the cell contains a high concentration of potassium ions (K), and the outside contains high concentrations of sodium ions (Na). At rest, the potential difference between the inside and outside of the cell membrane does not produce an electrical charge. This specific value is the resting potential. Due to changes in the external environment of the cell, the potential on its membrane constantly fluctuates, and if it increases and the cell reaches its electrical threshold for excitation, there is a sharp change in the electrical charge of the membrane, and it begins to conduct an action potential along the axon to the innervated muscle. By the way, in large muscle groups, one motor nerve can innervate up to 2-3 thousand muscle fibers.

In the diagram below you can see an example of the path a nerve impulse takes from the moment a stimulus occurs to the receipt of a response to it in each individual system.

Nerves connect to each other through synapses, and to muscles through neuromuscular junctions. Synapse- this is the point of contact between two nerve cells, and - the process of transmitting an electrical impulse from a nerve to a muscle.

Synaptic connection: 1- neural impulse; 2- receiving neuron; 3- axon branch; 4- synaptic plaque; 5- synaptic cleft; 6- neurotransmitter molecules; 7- cellular receptors; 8- dendrite of the receiving neuron; 9- synaptic vesicles

Neuromuscular contact: 1- neuron; 2- nerve fiber; 3- neuromuscular contact; 4- motor neuron; 5- muscle; 6- myofibrils

Thus, as we have already said, the process of physical activity in general and muscle contraction in particular is completely controlled by the nervous system.

Conclusion

Today we learned about the purpose, structure and classification of the human nervous system, as well as how it is related to his motor activity and how it affects the functioning of the whole organism as a whole. Since the nervous system is involved in regulating the activity of all organs and systems of the human body, including, and perhaps primarily, the cardiovascular system, then in the next article in the series about the systems of the human body, we will move on to its consideration.

Nerve endings are located throughout the human body. They have a vital function and are an integral part of the entire system. The structure of the human nervous system is a complex branched structure that runs through the entire body.

The physiology of the nervous system is a complex composite structure.

The neuron is considered the basic structural and functional unit of the nervous system. Its processes form fibers that are excited when exposed and transmit impulses. The impulses reach the centers where they are analyzed. Having analyzed the received signal, the brain transmits the necessary reaction to the stimulus to the appropriate organs or parts of the body. The human nervous system is briefly described by the following functions:

• providing reflexes;
• regulation of internal organs;
• ensuring the interaction of the body with the external environment, by adapting the body to changing external conditions and irritants;
• interaction of all organs.

The importance of the nervous system lies in ensuring the vital functions of all parts of the body, as well as the interaction of a person with the outside world. The structure and functions of the nervous system are studied by neurology.

Structure of the central nervous system

The anatomy of the central nervous system (CNS) is a collection of neuronal cells and neural processes of the spinal cord and brain. A neuron is a unit of the nervous system.

The function of the central nervous system is to ensure reflex activity and process impulses coming from the PNS.

Features of the structure of the PNS

Thanks to the PNS, the activity of the entire human body is regulated. The PNS consists of cranial and spinal neurons and fibers that form ganglia.

Its structure and functions are very complex, so any slightest damage, for example damage to blood vessels in the legs, can cause serious disruption to its functioning. Thanks to the PNS, all parts of the body are controlled and the vital functions of all organs are ensured. The importance of this nervous system for the body cannot be overestimated.

The PNS is divided into two divisions - somatic and autonomic system PNS.

Performs double work - collecting information from the senses, and further transmitting this data to the central nervous system, as well as ensuring the motor activity of the body by transmitting impulses from the central nervous system to the muscles. Thus, it is the somatic nervous system that is the instrument of human interaction with the outside world, as it processes signals received from the organs of vision, hearing and taste buds.

Ensures the performance of the functions of all organs. It controls the heartbeat, blood supply, and breathing. It contains only motor nerves that regulate muscle contraction.

To ensure the heartbeat and blood supply, the efforts of the person himself are not required - this is controlled by the autonomic part of the PNS. The principles of the structure and function of the PNS are studied in neurology.

Departments of the PNS

The PNS also consists of the afferent nervous system and the efferent nervous system.

The afferent region is a collection of sensory fibers that process information from receptors and transmit it to the brain. The work of this department begins when the receptor is irritated due to any impact.

The efferent system differs in that it processes impulses transmitted from the brain to effectors, that is, muscles and glands.

One of the important parts of the autonomic division of the PNS is the enteric nervous system. The enteric nervous system is formed from fibers located in the gastrointestinal tract and urinary tract. The enteric nervous system controls the motility of the small and large intestines. This section also regulates the secretions released in the gastrointestinal tract and provides local blood supply.

The importance of the nervous system is to ensure the functioning of internal organs, intellectual function, motor skills, sensitivity and reflex activity. The child’s central nervous system develops not only during the prenatal period, but also during the first year of life. Ontogenesis of the nervous system begins from the first week after conception.

The basis for brain development is formed already in the third week after conception. The main functional nodes are identified by the third month of pregnancy. By this time, the hemispheres, trunk and spinal cord have already been formed. By the sixth month, the higher parts of the brain are already better developed than the spinal part.

By the time a baby is born, the brain is the most developed. The size of the brain in a newborn is approximately an eighth of the child’s weight and ranges from 400 g.

The activity of the central nervous system and PNS is greatly reduced in the first few days after birth. This may include an abundance of new irritating factors for the baby. This is how the plasticity of the nervous system manifests itself, that is, the ability of this structure to be rebuilt. As a rule, the increase in excitability occurs gradually, starting from the first seven days of life. The plasticity of the nervous system deteriorates with age.

Types of CNS

In the centers located in the cerebral cortex, two processes simultaneously interact - inhibition and excitation. The rate at which these states change determines the types of nervous system. While one part of the central nervous system is excited, another is slowed down. This determines the features of intellectual activity, such as attention, memory, concentration.

Types of the nervous system describe the differences between the speed of inhibition and excitation of the central nervous system in different people.

People may differ in character and temperament, depending on the characteristics of the processes in the central nervous system. Its features include the speed of switching neurons from the process of inhibition to the process of excitation, and vice versa.

The types of nervous system are divided into four types.

• The weak type, or melancholic, is considered the most predisposed to the occurrence of neurological and psycho-emotional disorders. It is characterized by slow processes of excitation and inhibition. The strong and unbalanced type is choleric. This type is distinguished by the predominance of excitation processes over inhibition processes.
• Strong and agile - this is a type of sanguine person. All processes occurring in the cerebral cortex are strong and active. A strong but inert, or phlegmatic type, is characterized by a low speed of switching nervous processes.

The types of the nervous system are interconnected with temperaments, but these concepts should be distinguished, because temperament characterizes a set of psycho-emotional qualities, and the type of the central nervous system describes physiological characteristics processes occurring in the central nervous system.

CNS protection

The anatomy of the nervous system is very complex. The central nervous system and PNS suffer due to the effects of stress, overexertion and lack of nutrition. For the normal functioning of the central nervous system, vitamins, amino acids and minerals are necessary. Amino acids take part in brain function and are building materials for neurons. Having figured out why vitamins and amino acids are needed and why, it becomes clear how important it is to provide the body with the necessary amount of these substances. Glutamic acid, glycine and tyrosine are especially important for humans. The regimen for taking vitamin-mineral complexes for the prevention of diseases of the central nervous system and PNS is selected individually by the attending physician.

Damage to the beams, congenital pathologies and abnormalities in brain development, as well as the action of infections and viruses - all this leads to disruption of the central nervous system and PNS and the development of various pathological conditions. Such pathologies can cause a number of very dangerous diseases- immobilization, paresis, muscle atrophy, encephalitis and much more.

Malignant neoplasms in the brain or spinal cord lead to a number of neurological disorders. If an oncological disease of the central nervous system is suspected, an analysis is prescribed - histology of the affected parts, that is, an examination of the composition of the tissue. A neuron, as part of a cell, can also mutate. Such mutations can be identified by histology. Histological analysis is carried out according to the doctor’s indications and consists of collecting the affected tissue and its further study. For benign formations, histology is also performed.

The human body contains many nerve endings, damage to which can cause a number of problems. Damage often leads to impaired mobility of a body part. For example, an injury to the hand can lead to pain in the fingers and impaired movement. Osteochondrosis of the spine can cause pain in the foot due to the fact that an irritated or compressed nerve sends pain impulses to receptors. If the foot hurts, people often look for the cause in a long walk or injury, but the pain syndrome can be triggered by damage to the spine.

If you suspect damage to the PNS, as well as any related problems, you should be examined by a specialist.