Basic properties and functions of the elements of the nervous system. The value of the nervous system. Functions of the nervous system. The development of the genital organs of the child. puberty

Nervous system consists of tortuous networks of nerve cells that make up various interconnected structures and control all the activities of the body, both desired and conscious actions, and reflexes and automatic actions; the nervous system allows us to interact with the outside world, and is also responsible for mental activity.

consists of many nerves that go to the brain (brain pairs) and spinal cord (vertebral nerves); acts as a transmitter of sensory stimuli to the brain and commands from the brain to the organs responsible for their execution. The autonomic nervous system controls the functions of numerous organs and tissues through antagonistic effects: the sympathetic system is activated during anxiety, while the parasympathetic system is activated at rest.

As known, nervous system- the center of activity of the whole organism, it performs two main functions: 1) information transfer function for which they are responsible peripheral nervous system and associated receptors (sensors located in the skin, eyes, ears, mouth, etc.), and effectors (glands and muscles). 2) The second important function of the nervous system is integration and processing received information and programming the most appropriate response.

This function belongs central nervous system and includes a wide range of processes - from the simplest reflexes at the level of the spinal cord to the most complex mental operations at the level of higher parts of the brain. The central nervous system consists of the spinal cord and various brain structures. Damage or inadequate functioning of any part of the nervous system causes specific disorders in the functioning of the body and psyche. The nature of the usefulness and adequacy of the functioning of the brain most strongly affects the psyche, especially cerebral cortex.

In order for a person's behavior to be successful, it is necessary that his internal states, the external conditions in which the person is located, and the practical actions taken by him correspond to each other. At the physiological level, the function of combining (integrating) all this is provided by nervous system. The human nervous system consists of two sections: central and peripheral. The central includes the brain, diencephalon and spinal cord. The rest of the nervous system belongs to the peripheral.

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

Almost all departments of the central and peripheral nervous system are involved in the processing of information coming through external and internal receptors located on the periphery of the body and in the organs themselves. Work is associated with higher mental functions, with thinking and consciousness of a person. cerebral cortex(c.g.m.) and subcortical structures included in the forebrain.

The central nervous system is connected with all organs and tissues of the body through nerves coming out of the brain and spinal cord. They carry information that enters the brain from the external environment and conduct it in the opposite direction to individual parts and organs of the body. Nerve fibers that enter the brain from the periphery are called afferent, and those that conduct impulses from the center to the periphery are efferent.

C.Sc. is a collection of nerve cells neurons. A nerve cell is made up of the body of a neuron.

Tree-like processes extending from the bodies of nerve cells are called dendrites. One of these processes is elongated and connects the bodies of some neurons with the bodies or dendrites of other neurons. It is called axon. Part of the axons is covered with a special myelin sheath, which contributes to faster conduction of the impulse along the nerve.

The places where nerve cells meet each other are called synapses. Through them, nerve impulses are transmitted from one cell to another. For the most part, neurons are specialized, i.e. perform in the work ts.n.s. specific functions: conduction of nerve impulses from receptors to the central nervous system. (“sensory neuron”), conduction of nerve impulses from the c.n.s. to the organs of movement ("motor neuron") and the conduction of nerve impulses from one section of the c.n.s. to another (“local network neuron”).

At the periphery of the human body, in internal organs and tissues, cells with their axons approach receptors- miniature organic devices designed to perceive various types of energy - mechanical, electromagnetic, chemical and others - and convert it into the energy of nerve impulses. All structures of the body, external and internal, are permeated with a mass of various receptors. There are especially many of them in the sense organs: the eye, ear, skin surface in the most sensitive places, tongue, internal cavities of the nose.

A special role in the brain is played by the right and left cerebral hemispheres, as well as their main lobes: frontal, parietal, occipital and temporal.

I.P. Pavlov introduced the concept analyzer. This is a relatively autonomous organic system that ensures the processing of specific sensory information at all levels of its passage through the central nervous system. Accordingly, the main sense organs are distinguished by visual, auditory, gustatory, skin and some other analyzers.

Each analyzer consists of three anatomically different sections that perform specialized functions in its work: the receptor, nerve fibers and the central section, which is the part of the central nervous system where the corresponding stimuli are perceived, processed, memories of them are stored.

3. The structure of the surface of the cerebral cortex. It is the upper layer of the forebrain, formed mainly by neurons, their processes-dendrites and bundles of axons going from these cells down to the brain regions. According to the distribution of neurons in the layers of the cortex, their size and shape, the entire c.g.m. divided into a number of areas: occipital, parietal, frontal, temporal.

In c.g.m. impulses come from the subcortical structures and nerve formations of the brain stem; it also carries out the basic mental functions of a person.

Each mental process, state or property of a person is in a certain way connected with the work of the entire central nervous system. Sensations arise as a result of processing ts.n.s. effects on different sense organs of different types of energy. It enters the receptors in the form of physical stimuli, is converted, and then transferred to the central nervous system. and finally processed, turning into sensations, into c.g.m..

Both hemispheres, left and right, play different roles in perception and image formation. For right hemisphere characterized by a high speed of work on identification, its accuracy and clarity. This way of identifying objects can be defined as an integral-synthetic, holistic par excellence, structural-semantic. The right hemisphere probably compares the image with some standard stored in the memory based on the selection of some informative features in the perceived object. With the same left hemisphere an analytical approach to the formation of an image is carried out, which is associated with a sequential enumeration of its elements according to a specific program. But the left hemisphere, working in isolation, is apparently unable to integrate the perceived and selected elements into a coherent image. With its help, phenomena are classified and assigned to a certain category through the designation of a word. Thus, both hemispheres of the brain simultaneously participate in perception with different functions.

The specialization of the cerebral hemispheres reaches its highest development in humans. It is known that approximately 90% of people are dominated by the left hemisphere of the brain, in which the centers of speech are located. Depending on which hemisphere a person has is better developed, functions more actively, their own distinctive differences appear in the human psyche, his abilities.

The individuality of a person is largely determined by the specifics of the interaction of individual hemispheres of the brain. For the first time these relations were experimentally studied in the 60s of the XX century. professor of psychology at the California Institute of Technology Roger Sperry (in 1981 he was awarded the Nobel Prize for research in this area).

It turned out that in right-handers, the left hemisphere is responsible not only for speech, but also for writing, counting, verbal memory, and logical reasoning. The right hemisphere, on the other hand, has an ear for music, easily perceives spatial relationships, understanding forms and structures immeasurably better than the left, and is able to recognize the whole by part. True, there are deviations from the norm: either both hemispheres turn out to be musical, then the right one finds a supply of words, and the left one has ideas about what these words mean. But the pattern is basically preserved: both hemispheres solve the same task from different points of view, and if one of them fails, the function for which it is responsible is also violated. When the composers Ravel and Shaporin had a hemorrhage in the left hemisphere, both could no longer speak and write, but continued to compose music, not forgetting musical notation, which had nothing to do with words and speech.

Modern research confirmed that the right and left hemispheres have specific functions and the predominance of the activity of one or another hemisphere has a significant impact on the individual characteristics of a person's personality.

Experiments showed that when the right hemisphere was turned off, people could not determine the current time of day, season, navigate in a particular space - they could not find their way home, did not feel "higher or lower", did not recognize the faces of their acquaintances, did not perceive the intonation of words, etc. . P.

A person is not born with a functional asymmetry of the hemispheres. Roger Sperry found that in split-brain patients, especially the younger ones, rudimentary speech functions improve over time. The “illiterate” right hemisphere can learn to read and write in a few months as if it already knew all this, but forgot.

The speech centers in the left hemisphere develop mainly not from speaking, but from writing: the exercise in writing activates, trains the left hemisphere. But it's not about the participation of the right hand. If a right-handed European boy is sent to study in a Chinese school, the centers of speech and writing will gradually move to the right hemisphere, because in the perception of the hieroglyphs that he learns, the visual zones participate immeasurably more actively than the speech zones. The reverse process will occur in a Chinese boy who moved to Europe. If a person remains illiterate for life and is busy with routine work, interhemispheric asymmetry will hardly develop in him. Thus, the functional specificity of the hemispheres changes under the influence of both genetic and social factors. The asymmetry of the hemispheres of the brain is a dynamic formation, in the process of ontogenesis there is a gradual increase in the asymmetry of the brain (the most pronounced asymmetry of the hemispheres is observed in middle age, and by old age it gradually levels off), in the case of damage to one hemisphere, partial interchangeability of functions is possible and compensation for the work of one hemisphere due to the other .

It is the specialization of the hemispheres that allows a person to consider the world from two different points of view, to cognize its objects, using not only verbal and grammatical logic, but also intuition.

But it should be emphasized that the normal implementation of any function is the result of the work of the entire brain, both the left and right hemispheres.

A special role in the regulation of many mental processes, properties and states of a person is played by reticular formation. It is a collection of sparse, resembling a thin network (hence the name - reticular) neural structures, anatomically located in the spinal cord, in the medulla oblongata and in the hindbrain.

Lateral branches of the fibers of all sensory systems go to the reticular formation. It is also associated with nerve fibers coming from c.g.m. and from the cerebellum. In turn, the fibers of the reticular formation conduct impulses in a downward direction, to the cerebellum and to the spinal cord.

The reticular formation has a significant effect on the electrical activity of the brain, on the functional state of the c.g.m., subcortical centers, cerebellum and spinal cord. It is also directly related to the regulation of basic life processes: blood circulation, respiration, etc. The destruction of the reticular formation of the brain stem causes a state of prolonged sleep. The ascending part of the reticular formation is associated with an increase and decrease in the sensitivity to.g.m. It plays an important role in controlling the mechanisms of sleep and wakefulness, learning and attention. K.g.m. through descending nerve fibers, it is also able to influence the reticular formation, which, apparently, is associated with the conscious psychological self-regulation of a person.

With the evolutionary complication of multicellular organisms, 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 should have appeared along with the preservation and complication of the mechanisms for regulating the functions of individual cells with the help of signaling molecules. Adaptation of multicellular organisms to changes in the environment of existence could be carried out on the condition that new regulatory mechanisms would be able to provide fast, adequate, targeted responses. These mechanisms must be able to memorize and retrieve from the memory apparatus information about previous effects on the body, as well as have other properties that ensure effective adaptive activity of the body. They were 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 activity 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 subdivided into the hindbrain (and the pons), the reticular formation, subcortical nuclei,. The bodies form the gray matter of the CNS, 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 (stimuli) of the external and internal environment of the body. Recall that any cells can perceive various signals of the environment of existence with the help of specialized cellular receptors. However, they are not adapted to the perception of a number of vital signals and cannot instantly transmit information to other cells that perform the function of regulators of integral adequate reactions of the body 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 change, vibration, acceleration, compression, stretching), as well as signals of a complex nature (color, complex sounds, words).

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

The signals and the results of their analysis are used by the nervous system to response organization 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 variants of responses to influences 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 of existence, the nervous system performs the functions homeostasis regulation, ensure functional interaction organs and tissues and their integration into a single whole body.

Thanks to the nervous system, an adequate interaction of the organism with the environment is carried out not only through the organization of responses by effector systems, but also through its own mental reactions - emotions, motivations, 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 cranial cavity and spinal canal. The human brain contains over 100 billion nerve cells. (neurons). Accumulations 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 CNS, and the processes of these cells, uniting into pathways, form the white matter. In addition, the structural part of the CNS is glial cells that form neuroglia. The number of glial cells is about 10 times the number of neurons, and these cells make up the majority of the mass of the central nervous system.

According to the features of the functions performed and the structure, the nervous system is divided into somatic and autonomous (vegetative). Somatic structures include the structures of the nervous system, which provide the perception of sensory signals mainly from the external environment through the sense organs, and control the work of the striated (skeletal) muscles. The autonomic (vegetative) nervous system includes structures that provide the perception of signals mainly from the internal environment of the body, regulate the work 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 a role in the regulation of life processes. Among them, the basal nuclei, brain stem structures, spinal cord, peripheral nervous system.

The 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 extending from the central nervous system to various organs.

Rice. 1. The structure of the nervous system

Rice. 2. Functional division of the nervous system

Significance of the nervous system:

• unites the organs and systems of the body into a single whole;
• regulates the work of all organs and systems of the body;
• carries out the connection of the organism with the external environment and its adaptation 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 strongly branch and form many synapses with other cells, which determines their leading role in the perception of information by the neuron. The axon starts from the cell body with the axon mound, which is the generator of a nerve impulse, which is then carried along the axon to other cells. The axon membrane in the synapse contains specific receptors that can respond to various mediators or neuromodulators. Therefore, the process of mediator 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. Scheme of a neuron (according to I.F. Ivanov): a - structure of a neuron: 7 - body (pericaryon); 2 - core; 3 - dendrites; 4.6 - neurites; 5.8 - myelin sheath; 7- collateral; 9 - node interception; 10 — a kernel of a lemmocyte; 11 - nerve endings; b — types of nerve cells: I — unipolar; II - multipolar; III - bipolar; 1 - neuritis; 2 - dendrite

Usually, 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 the cell body.

Axons, in addition to the 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 axon 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 in the central nervous system, there are glial cells, occupying half the volume of the brain. Peripheral axons are also surrounded by a sheath of glial cells - lemmocytes (Schwann cells). Neurons and glial cells are separated by intercellular clefts that communicate with each other and form a fluid-filled intercellular space of neurons and glia. Through this space there is an exchange of substances between nerve and glial cells.

Neuroglial cells perform many functions: supporting, protective and trophic role 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 body 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 provided by the central nervous system.

Coordinating: the functions of various organs and systems of the body must proceed in a coordinated manner, since only with this way of life it is possible to maintain the constancy of the internal environment, as well as successfully adapt to changing environmental conditions. The coordination of the activity of the elements that make up the body is carried out by the central nervous system.

Regulatory: the central nervous system regulates all the 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, the intensity of metabolic processes in the tissues of the body, which underlies the formation of reactions that are adequate to the ongoing changes in the internal and external environment.

Adaptive: the central nervous system communicates the body with the external environment by analyzing and synthesizing various information coming to it from sensory systems. This makes it possible to restructure the activities of various organs and systems in accordance with changes in the environment. It performs the functions of 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 an organism, its systems, organs, tissues to changing environmental conditions is called regulation. The regulation provided jointly by the nervous and hormonal systems is called neurohormonal regulation. Thanks to the nervous system, the body carries out its activities on the principle of a reflex.

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

Reflex in Latin means "reflection". The term "reflex" was first proposed by the Czech researcher I.G. Prohaska, who developed the doctrine of reflective actions. The further development of the reflex theory is associated with the name of I.M. Sechenov. He believed that everything unconscious and conscious is accomplished by the type of reflex. But then there were no methods for an objective assessment of brain activity that could confirm this assumption. Later, an objective method for assessing brain activity was developed by Academician I.P. Pavlov, and he received the name of 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, which are formed on the basis of unconditioned reflexes due to the formation of temporary connections. Academician P.K. Anokhin showed that the whole variety 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, which ensures 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 according to the reflex principle. Reflex arc: 1 - receptor; 2 - afferent path; 3 - nerve center; 4 - efferent path; 5 - working body (any organ of the body); MN, motor neuron; M - muscle; KN — command neuron; SN — sensory neuron, ModN — modulatory neuron

The receptor neuron's dendrite contacts the receptor, its axon goes to the CNS and interacts with the intercalary neuron. From the intercalary neuron, the axon goes to the effector neuron, and its axon goes to the periphery to the executive organ. Thus, a reflex arc is formed.

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

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

The 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 different parts of the central nervous system. The nerve center receives impulses from receptors along the afferent pathway, analyzes and synthesizes this information, and then transmits the generated action program along efferent fibers to the peripheral executive organ. And the working body carries out its characteristic activity (the muscle contracts, the gland secretes a secret, 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 the action acceptor of the back afferent 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 a 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. common to all animals of this species. They are constant throughout life and arise in response to adequate stimulation of the receptors. Unconditioned reflexes are also classified according to their biological significance: food, defensive, sexual, locomotor, indicative. According to the location of the receptors, these reflexes are divided into: exteroceptive (temperature, tactile, visual, auditory, gustatory, etc.), interoceptive (vascular, cardiac, gastric, intestinal, etc.) and proprioceptive (muscular, tendon, etc.). By the nature of the response - to motor, secretory, etc. By finding the nerve centers through which the reflex is carried out - to the spinal, bulbar, mesencephalic.

Conditioned reflexes - reflexes acquired by the organism in the course of 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.

At the heart of modern ideas about the reflex activity of the body is 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 through the feedback link in the form of reverse afferentation, which is an essential 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, the integrity of all links is necessary for the implementation of the reflex.

Properties of nerve centers

Nerve centers have a number of characteristic functional properties.

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

In the nerve centers, summation of excitations can occur.

There are two main ways of summation: temporal and spatial. At temporary summation several excitatory impulses come to the neuron through one synapse, are summed up and generate an action potential in it, and spatial summation manifests itself in the case of receipt of impulses to one neuron through different synapses.

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

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

Nerve centers, unlike nerve fibers, are capable of rapid fatigue. Synaptic fatigue during 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 flow 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 in synapses after a short stimulation of the afferent pathways. With frequent use of synapses, the synthesis of receptors and mediator is accelerated.

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

CNS coordination activity 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 neuronal structures, as well as the interaction between nerve centers, which 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 respiration and swallowing, when during swallowing the center of respiration is inhibited, the epiglottis closes the entrance to the larynx and prevents food or liquid from entering the airways. 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 can be the articulation of speech, the act of swallowing, gymnastic movements that require the coordinated contraction and relaxation of many muscles.

Principles of coordination activity

• Reciprocity - mutual inhibition of antagonistic groups of neurons (flexor and extensor motoneurons)
• End neuron - activation of an efferent neuron from different receptive fields and competition between different afferent impulses for a given motor neuron
• Switching - the process of transferring activity from one nerve center to the antagonist nerve center
• Induction - change of excitation by 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 the function
• Dominant - 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.

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

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 implementing the same reaction triggered by the final efferent neuron in the hierarchical nervous circuit, to which the axons of many other nerve cells converge. An example of a classic final pathway is the motor neurons of the anterior horns of the spinal cord or the motor nuclei of the cranial nerves, which directly innervate the muscles with their axons. The same motor response (for example, bending the arm) can be triggered by the receipt of impulses to these neurons from the 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 by different sense organs (to light, sound, gravitational, pain or mechanical effects).

Principle of divergence 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. Due to divergent connections, signals are widely distributed (irradiated) and many centers located at different levels of the CNS are quickly involved in the response.

The principle of feedback (reverse afferentation) consists in the possibility of transmitting information about the ongoing reaction (for example, about movement from muscle proprioceptors) back to the nerve center that triggered it, via afferent fibers. Thanks to feedback, a closed neural circuit (circuit) is formed, through which it is possible to control the progress of the reaction, adjust the strength, duration and other parameters of the reaction, if they have not been implemented.

The participation of feedback can be considered on the example of the implementation of the flexion reflex caused by mechanical action on skin receptors (Fig. 5). With reflex contraction of the flexor muscle, the activity of proprioreceptors and the frequency of sending nerve impulses along the afferent fibers to the a-motoneurons of the spinal cord, which innervate this muscle, change. As a result, a closed control loop is formed, in which the role of the feedback channel is played by afferent fibers that transmit information about the contraction to the nerve centers from the muscle receptors, and the role of the direct communication channel is played by the efferent fibers of motor neurons going to the muscles. Thus, the nerve center (its motor neurons) receives information about the change in the state of the muscle caused by the transmission of impulses along the motor fibers. Thanks to the 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 scheme in neural circuits of the simplest reflexes

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

Dominant principle is also realized on the basis of the characteristics of the interaction between the nerve centers. The neurons of the dominant, most active center (focus of excitation) have persistent high activity and suppress excitation in other nerve centers, subjecting 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 be in a state of excitation 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 an important event experienced by a person, when all his thoughts and actions somehow become connected with this event.

Dominant Properties

• Hyperexcitability
• Excitation persistence
• Excitation inertia
• Ability to suppress subdominant foci
• Ability to sum excitations

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

The modern understanding of the structure and function of the CNS is based on neural theory, which is a special case of cell theory. The neural theory, which considers the brain as the result of the functional association of individual cellular elements - neurons, became widespread and recognized at the beginning of the 20th century.

Of great importance for its recognition were the studies of the Spanish scientist neurohistologist R. Cajal and the English physiologist C. Sherrington. The final evidence of the complete structural isolation of nerve cells was obtained using an electron microscope.

Scientists have proven that the nervous system is built from two types of cells: nervous and glial. At the same time, the number of glial cells is 8-9 times higher than the number of nerve cells. Despite this, it is nerve cells that provide all the variety of processes associated with the transmission and processing of information.

Thus, the main structural and functional unit of the nervous system is neuron(nerve cell, neurocyte) (Fig. 1).

Fig.1. Nerve cells:

A - multipolar neuron; 1 - neurite;

B - unipolar neuron; 2 - dendrite

B - bipolar neuron

The neuron is made up of body(soma), which contains various intracellular organelles necessary for the life of the cell. In addition, all the processes of chemical synthesis take place in the body of the neuron, from where the products of this synthesis enter the various processes that extend from the body of the neuron. The body of the neuron is covered with a special membrane - membrane. Cells originate from the body processes nerve cell - dendrites and axons. In most cases, the dendrites are highly branched, as a result of which their total surface significantly exceeds the surface of the cell body. According to the number of processes present, neurons are classified as follows:

1) bipolar neurons - have two processes;

2) multipolar neurons - have more than two processes;

3) unipolar neurons - have one well-defined process.

According to scientists, the human brain consists of 2.5 multiplied by 10 to the tenth power of neurons. If you calculate this number, then it will practically coincide with the number that determines the number of stars in the Galaxy.

The main functional purpose of the processes is to ensure the propagation of nerve impulses. Conduction of a nerve impulse from the body of a neuron to another nerve cell or to a working tissue, organ is carried out along the axon (neurite) (from the Greek axon - axis). Any neuron can have only one axon. The processes that conduct nerve impulses to the body of the neuron are called dendrites(from the Greek dendron, meaning tree).

It should be noted that a nerve cell is capable of transmitting a nerve impulse in only one direction - from the dendrite through the body of the nerve cell to the axon and through it further to the destination.

In accordance with the morphofunctional characteristics, three types of neurons are distinguished.

1. sensitive, receptor, or afferent neurons. The bodies of these nerve cells are always located all over the brain or spinal cord, in the nodes (ganglia) of the peripheral nervous system. One of the processes extending from the body of the nerve cell follows to the periphery to one or another organ and ends there with a sensitive ending - a receptor that is able to transform the energy of external influence (irritation) into a nerve impulse. The second process is sent to the CNS, spinal cord or brain stem as part of the posterior roots of the spinal nerves or the corresponding cranial nerves.

Reception, i.e. the perception of irritation and the beginning of the spread of the nerve impulse along the nerve conductors to the centers, I.P. Pavlov attributed to the beginning of the analysis process.

2. Closing, intercalary, associative, or conductor, neuron. This neuron transfers excitation from the afferent (sensitive) neuron to the efferent ones. The essence of this process is to transfer the signal received by the afferent neuron to the efferent neuron for execution in the form of a response. I.P. Pavlov defined this action as "a phenomenon of nervous closure." The trailing (intercalary) neurons lie within the CNS.

3. Effector, efferent (motor or secretory) neuron. The bodies of these neurons are located in the central nervous system (or on the periphery - in the sympathetic, parasympathetic nodes).

Neurons in the nervous system, coming into contact with each other, form chains along which nerve impulses are transmitted (moving). The transmission of a nerve impulse from one neuron to another occurs at the points of their contacts and is provided by a special kind of formations called interneuronal synapses. Synapses are usually divided into axosomatic, when the axon endings of one neuron form contacts with the body of another neuron, and axodendritic, when the axon comes into contact with the dendrites of another neuron. Individual nerve cells form up to 2000 synapses each.

Nerve processes covered with sheaths form nerve fibers. There are two main groups of nerve fibers:

Myelin (pulp);

Myelin-free (non-fleshy).

Nerves are built from pulpy and non-pulmonic nerve fibers and connective tissue membranes. Pulp nerve fibers are part of the sensory and motor nerves; non-fleshy nerve fibers mainly belong to the autonomic nervous system.

Between the nerve fibers is a thin layer of connective tissue - endnervium.

Outside, the nerve is covered with fibrous connective tissue - nerves.

The following physiological properties of the nerve fiber are distinguished:

Excitability. In 1791, the French scientist Galvani put forward the idea of ​​the existence of "living electricity" in nerves and muscles. His compatriot Matteuchi in the 40s of the XIX century received the first evidence of the electrical nature of the nerve impulse, and another scientist Helmholtz, who later became a famous physicist, in 1850 measured the speed of the nerve impulse, determining its transmission along the nerve not as a physical conduction, but as an active biological process. In this regard, nerve impulses are called action potentials. After the research, the idea that the neuron is a cell designed to generate impulses, which are the direct means of signal exchange between nerve cells, has become widespread.

Conductivity. As we noted, the function of the axon is to conduct nerve impulses. The conduction of a nerve impulse can be likened to the propagation of an electric current. As a rule, the action potential originates in the initial segment of the axon closest to the cell body and runs along the axon to its endings. Due to various ions (sodium, potassium, etc.), which constantly move as a result of diffusion through the membrane of a living cell, a charge is formed on its surface, which is called membrane potential. At rest, a negative potential is recorded on the inside of the membrane. A constant negative potential recorded on neurons is commonly called the resting membrane potential, and this phenomenon is called polarization. A decrease in the degree of polarization (shift of the potential to zero) is called depolarization. The increase is hyperpolarization.

nerve fiber integrity. Excitation propagates along the nerve fiber only while maintaining its anatomical and physiological integrity. Loss of structural and physiological properties as a result of cooling, exposure to toxic substances, etc. leads to impaired conduction of the nerve fiber.

Bilateral conduction of excitation along the nerve fiber. This phenomenon was discovered by the Russian scientist R.I. Rabukhin, who showed that excitation, having arisen in any area of ​​\u200b\u200bthe nerve fiber, spreads in both directions, regardless of whether this fiber is centripetal or centrifugal.

Property of isolated nerve impulse conduction. If excitation has arisen in one nerve fiber, then it cannot pass to the neighboring nerve fiber located in the same nerve. The importance of this property is manifested in the fact that most nerves are mixed, consisting of thousands of functionally different nerve fibers.

Relative restlessness of the nerve. This property was singled out in 1884 by the scientist N.E. Vvedensky, who showed that the nerve retains the ability to conduct excitation even with prolonged continuous stimulation, i.e. the nerve is practically inexhaustible. Only changes in the morphological and functional properties of the nerve can gradually suppress its conduction.

Functional lability of nervous tissue. This concept was also formulated by N.E. Vvedensky in 1892, who discovered that a nerve can respond to a given frequency of stimulation with the same frequency of excitation only up to a certain limit. The measure of lability, according to N.E. Vvedensky, is the largest number of excitations that a tissue can reproduce in 1 second in full accordance with the frequency of irritations. For example, the largest number of impulses of the warm-blooded motor nerve is up to 1000 per 1 sec. Excitable tissue, depending on the functional state, is able to change its lability both in the direction of its decrease and increase. In this case, the excitable tissue begins to assimilate new, higher (or lower) rhythms of activity previously inaccessible to it. A decrease in functional lability in the process of life activity leads to inhibition of the function.

The set of nerve cells (neurons) located at different levels of the central nervous system, sufficient for the adaptive regulation of the function of an organ according to the needs of the body, is called nerve centers. For example, the neurons of the respiratory center are located in the spinal cord, and in the medulla oblongata, and in the bridge. However, among several groups of cells located at different levels of the CNS, as a rule, the main part of the center stands out. Thus, the main part of the respiratory center is located in the medulla oblongata and includes inspiratory and expiratory neurons.

The nerve center realizes its influence on effectors either directly with the help of efferent impulses of the somatic and autonomic nervous system, or through the activation and production of the corresponding hormones.

It should also be noted that the space between neurons is filled with cells glia. Glia provides structural and metabolic support for the network of neurons, ensures their relative position. Among glial cells, there are:

1)astrocytes, cells located in the brain and spinal cord;

2)oligodendrocytes, closely connected in the central nervous system with long nerve pathways formed by axon launches, as well as with nerves;

3)ependymal cells that mainly form a continuous epithelial tissue lining the ventricles of the brain;

4)microglia, which consists of small cells scattered in the white and gray matter of the brain.

Questions for self-control:

What is a neuron?

What is its structure?

What is the function of the processes of a neuron?

What is a synapse?

Expand approaches to the classification of synapses.

Describe the types of neurons.

Describe the nerve fiber.

Describe the physiological properties of the nerve fiber.

What is a nerve center?

What is glia and what is its functional purpose?

Neuron - a highly specialized cell adapted for receiving, processing, integrating, storing and transmitting information. The neuron consists of a body and processes of two types: short branching dendrites and a long process - an axon.

Having a fundamentally common structure, neurons differ greatly in size, shape, number, branching, arrangement of dendrites, length and branching of the axon. There are two main types of neurons:

1. pyramidal - large neurons of different sizes, on which impulses from different sources converge. They are divided into two types:

a) afferent;

b) efferent.

2. intercalary (interneurons) - smaller in size, diverse in the spatial arrangement of processes:

a) spindle-shaped;

b) stellate;

c) basket.

Signals ( nerve impulses ) from the organs and tissues of the human body and from the external environment that acts on the surface of the body and sensory organs, they enter the spinal cord and brain through the nerves. There are complex processes of processing the received information. As a result, response signals also go from the brain along the nerves to the organs and tissues, causing the response of the body, which manifests itself in muscle and secretory activity.

Rice. 12. Functioning of the nervous system

In the nervous system, nerve cells, forming contacts ( synapses ) with other nerve cells, fold into circuits of neurons . Through them, nerve impulses are conducted from organs and tissues, where these impulses occur in the nerve endings, to the centers of the nervous system - to the brain. From the brain to the working organs (muscles, glands, etc.), nerve impulses also follow the chains of neurons.

Reflex -(from lat. reflexus- reflection, response) - the body's response to the effects of the external environment or changes in its internal state, performed with the participation of the nervous system.

reflex arc - a path consisting of chains of neurons along which a nerve impulse passes from sensitive nerve cells to a working organ.

All activity of the nervous system is based on reflex arcs, which can be:

1. simple - consists of three neurons;

2. complex - consist of many neurons (several intercalary).

Each reflex arc can be distinguished:

1. first neuron - sensitive or bringing - perceives influences, forms a nerve impulse and brings it to the brain (central nervous system);

2. last neuron - efferent or effector - carries a nerve impulse from the brain to the working organ, includes this organ in work, causes the effect of action;

3. intermediate neuron (one or more) - intercalary or conductive - conduct nerve impulses from the bringing, sensitive neuron to the last, taking out, efferent neuron.