NERVOUS REGULATION OF FUNCTIONS- a set of reactions of the central nervous system aimed at ensuring an optimal level of vital activity, maintaining homeostasis and the adequacy of the interaction of the organism with the environment.

At the heart of ideas about N. of river. f. lies the doctrine of the reflex (see). N. r. f. provides stabilization of the parameters fiziol, (biol.) constants (eg, blood pH), their restructuring to a new level, the formation of new types of motor and autonomic reactions, the provision of anticipatory reactions (i.e., the formation of a response based on conditioned reflex temporary connections).

N. r. f., participating in a single system of neurohumoral regulation (see), ensures the flow of adaptive reactions - from subcellular to behavioral (see Adaptation).

Allocate two main types of the system mechanisms underlying N. of river. f., - rigid (fixed) and flexible (non-fixed). Rigid mechanisms of N. river. f. are genetically fixed in the process of evolution and regulate the achievement of permanently existing goals (for example, the course of metabolic processes, the perception and processing of current information, etc.). Flexible mechanisms N. r. f. provide achievement by an organism of the momentary purposes, after achievement to-rykh cease to function.

At the heart of work of rigid mechanisms N. river. f. there are genotypic programs that predetermine efferent pathways of regulation; phenotypic influences affect only specific forms of implementation of these programs. So, for example, the genotypic regulation of the respiratory center consists in ensuring the alternation of the processes of inhalation and exhalation. Phenotypically, the duration of each phase and the amplitude of these processes can change in accordance with the momentary and needs of the organism.

Flexible, non-fixed mechanisms Y. R. f. are carried out by temporarily created neural ensembles. The leading principle of association is the dominant (see), providing synchronization of work of the nervous structures entering into ensemble. At the same time, the number, functional and structural affiliation of neurons included in the central link of the N. system of river. f., are determined by the tasks of regulation, as well as the dynamics of the formation and implementation of the program.

The N. program is being implemented. f. by means of efferent influences on executive bodies, work to-rykh provides adequate changes of regulated parameters. There are three types of such influences: triggering, causing active activity of the regulated structure or stopping it (for example, muscle contraction, secretion of cells of the gastric mucosa, cessation of secretion of liberin in the hypothalamus, etc.); adaptive, affecting the strength of the reaction and the ratio of its individual components in the process of performing the function, and the so-called. readiness influences (they form the level of readiness of the regulated structure to respond to starting and adaptive influences).

N. r. f. - a necessary link in the chain of reactions aimed at maintaining various fiziol, constants at an optimal level (see Homeostasis). Great value of N. of river. f. has in the implementation of compensation processes (see Compensatory processes).

Violations of N. river. f. are observed at any patol, process. These violations are polyetiological and can be caused by a pain sensation that creates a dominant that inhibits the usual mechanisms of regulation, exposure to microbial toxins, the development of general and local hypoxia, and others. f. as a result of development of vicious forms of compensation patol, process. The most common cause of N.'s disturbances p. f. with direct impact on c. n. With. are hemorrhages, tumors, injuries, etc. (see Nervous system, pathophysiology).

Bibliography: A and about\t in PK System mechanisms of higher nervous activity, M., 1979; B ern sh t e y n N. A. On the construction of movements, M., 1947; B e x t e-|) e in and N. P. Neurophysiological aspects of human mental activity, L., 1974, bibliogr.; You and l e in - with k and y N.N. Ecological physiology of the brain, L., 1979, bibliogr.; Medvedev V. I. Ideas of I. M. Sechenov in modern physiology. Physiol, human, v.5, JVe 3, p. 389, 1979; Miller J. A., a-l and n t e p E. and Pribram K. Plans and structure of behavior, trans. from English, M., 1964; M and with yu to N. S. Structure and correction of behavior, Minsk, 1980, bibliogr.; About r e l and L. A. Questions of higher nervous activity, M. - L., 1949; Pavl about in I. P. Complete works, vol. 1, M. - L., 1951; At about l t e r G. Living brain, ner. from English, M., 1966; III e p r and N Mr. Ch. S. Integrative activity of the nervous system, trans. from English, L., 1969; Ecological Physiology of Animals, ed. A. D. Slonim, part 3, L., 1979.

V. I. Medvedev.

The main role in the regulation of body functions and ensuring its integrity belongs to the nervous system. This mechanism of regulation is more perfect. Firstly, nerve influences are transmitted much faster than chemical influences, and therefore the body through the nervous system carries out rapid responses to the action of stimuli. Due to the significant speed of nerve impulses, the interaction between parts of the body is established quickly in accordance with the needs of the body.

Secondly, nerve impulses come to certain organs, and therefore the responses carried out through the nervous system are not only faster, but also more accurate than with humoral regulation of functions.

Reflex - the main form of nervous activity

All activity of the nervous system is carried out in a reflex way. With the help of reflexes, the interaction of various systems of the whole organism and its adaptation to changing environmental conditions are carried out.

With an increase in blood pressure in the aorta, the activity of the heart changes reflexively. In response to the temperature effects of the external environment, a person narrows or expands the blood vessels of the skin, under the influence of various stimuli, cardiac activity, breathing intensity, etc. reflexively change.

Thanks to reflex activity, the body quickly responds to various influences of the internal and external environment.

Irritations are perceived by special nerve formations - receptors. There are various receptors: some of them are irritated when the ambient temperature changes, others - when touched, others - when painful irritation, etc. Thanks to the receptors, the central nervous system receives information about all changes in the environment, as well as changes inside the body.

When the receptor is stimulated, a nerve impulse arises in it, which propagates along the centripetal nerve fiber and reaches the central nervous system. The central nervous system “knows” about the nature of irritation by the strength and frequency of nerve impulses. In the central nervous system, a complex process of processing the incoming nerve impulses takes place, and already along the centrifugal nerve fibers, the impulses from the central nervous system are sent to the executive organ (effector).

For the implementation of the reflex act, the integrity of the reflex arc is necessary (Fig. 2).

Experience 2

Immobilize the frog. To do this, wrap the frog in a gauze or linen napkin, leaving only the head open. At the same time, the hind legs should be extended, and the front legs should be tightly pressed to the body. Insert a dull blade of scissors into the frog's mouth and cut off the upper jaw with the skull. Do not destroy the spinal cord. A frog in which only the spinal cord is preserved, and the overlying sections of the central nervous system are removed, is called spinal. Secure the frog in the tripod by clamping the lower jaw with a clamp or by pinning the lower jaw to the stopper fixed in the tripod. Leave the frog hanging for a few minutes. On the restoration of reflex activity after removal of the brain, judge by the appearance of a response to the pinch. To prevent the skin from drying out, periodically lower the frog into a glass of water. Pour a 0.5% hydrochloric acid solution into a small glass, dip the frog's hind leg into it and observe the reflex withdrawal of the leg. Wash off the acid with water. On the hind foot, in the middle of the lower leg, make an annular incision in the skin and with surgical tweezers remove it from the bottom of the foot, making sure that the skin is carefully removed from all fingers. Dip the foot in the acid solution. Why doesn't the frog withdraw its limb now? In the same acid solution, lower the other leg of the frog, from which the skin has not been removed. How does the frog react now?

Disrupt the frog's spinal cord by inserting a dissecting needle into the spinal canal. Dip the leg, on which the skin is preserved, into the acid solution. Why does the frog not withdraw its leg now?

Nerve impulses during any reflex act, arriving in the central nervous system, are able to spread through its various departments, involving many neurons in the process of excitation. Therefore, it is more correct to say that the structural basis of reflex reactions is made up of neural circuits of centripetal, central and centrifugal neurons.

Feedback principle

There are both direct and feedback connections between the central nervous system and the executive organs. When the stimulus acts on the receptors, a motor reaction occurs. As a result of this reaction, in the executive organs (effectors) - muscles, tendons, articular bags - receptors are excited, from which nerve impulses enter the central nervous system. it secondary centripetal impulses, or feedback. These impulses constantly signal to the nerve centers about the state of the motor apparatus, and in response to these signals, new impulses arrive from the central nervous system to the muscles, including the next phase of movement or changing the movement in accordance with the conditions of activity.

Feedback is very important in the mechanisms of coordination carried out by the nervous system. In patients with impaired muscle sensitivity, movements, especially walking, lose their smoothness and become uncoordinated.

Conditioned and unconditioned reflexes

A person is born with a whole range of ready-made, innate reflex reactions. it unconditioned reflexes. These include acts of swallowing, sucking, sneezing, chewing, salivation, separation of gastric juice, maintaining body temperature, etc. The number of innate unconditioned reflexes is limited, and they cannot ensure the adaptation of the body to constantly changing environmental conditions.

On the basis of innate unconditioned reactions in the process of individual life, conditioned reflexes. These reflexes are very numerous in higher animals and man and play an enormous role in the adaptation of organisms to the conditions of existence. Conditioned reflexes have a signal value. Thanks to conditioned reflexes, the body is, as it were, warned in advance about the approach of something significant. By the smell of burning, a person and an animal learn about an approaching disaster, a fire; animals search for prey by smell, sounds or, on the contrary, escape from the attack of predators. On the basis of numerous conditional connections formed during an individual life, a person acquires life experience that helps him navigate in the environment.

In order to make the difference between unconditioned and conditioned reflexes clearer, let's take a (mental) excursion to the maternity hospital.

There are three main rooms in the maternity hospital: the delivery room, the neonatal room, and the mothers' room. After the baby is born, it is brought to the neonatal ward and given a little rest (usually 6-12 hours), and then taken to the mother to be fed. And only the mother will attach the child to the breast, as he grabs her with his mouth and begins to suck. Nobody taught this to a child. Sucking is an example of an unconditioned reflex.

Here is an example of a conditioned reflex. At first, as soon as the newborn gets hungry, he starts screaming. However, after two or three days in the neonatal ward, the following picture is observed: the feeding time is coming, and the children, one by one, begin to wake up and cry. The nurse takes them in turn and swaddles them, if necessary, washes them, and then puts them on a special gurney to take them to their mothers. The behavior of the children is very interesting: as soon as they are swaddled, put on a gurney and taken out into the corridor, they all fall silent as if on command. A conditioned reflex was developed for the time of feeding, for the situation before feeding.

To develop a conditioned reflex, it is necessary to reinforce the conditioned stimulus with an unconditioned reflex and repeat them. It took 5-6 times to coincide with swaddling, washing and laying on a gurney with subsequent feeding, which here plays the role of an unconditioned reflex, as a conditioned reflex developed: stop screaming, despite the ever-increasing hunger, wait a few minutes until the feeding begins. By the way, if you take the children out into the corridor and be late with feeding, then after a few minutes they start screaming.

Reflexes are simple and complex. All of them are interconnected and form a system of reflexes.

Experience 3

Develop a conditioned blinking reflex in humans. It is known that when a stream of air enters the eye, a person closes it. This is a protective, unconditioned reflex reaction. If now several times we combine the blowing of air into the eye with some indifferent stimulus (the sound of a metronome, for example), then this indifferent stimulus will become a signal that an air stream enters the eye.

To blow air into the eye, take a rubber tube connected to an air blower. Put a metronome nearby. Cover the metronome, pear and hands of the experimenter from the subject with a screen. Turn on the metronome and after 3 seconds press the bulb, blowing a stream of air into the eye. The metronome should continue to work when air is blown into the eye. Turn off the metronome as soon as the blink reflex occurs. After 5-7 minutes, repeat the combination of the metronome sound with air blowing into the eye. Continue the experiment until the blinking occurs only at the sound of the metronome, without blowing air. Instead of a metronome, you can use a bell, bell, etc.

How many combinations of a conditioned stimulus with an unconditioned stimulus were required to form a conditioned blinking reflex?

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. The 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 the 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 motoneurons 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) It 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.

Biology [A complete guide to preparing for the exam] Lerner Georgy Isaakovich

5.4. Nervous and endocrine systems. Neurohumoral regulation of vital processes of the body as the basis of its integrity, connection with the environment

5.4.1. Nervous system. General plan of the building. Functions

The main terms and concepts tested in the examination paper: autonomic nervous system, brain, hormones, humoral regulation, motor zone, glands, endocrine, glands, mixed secretion, cerebral cortex, parasympathetic nervous system, peripheral nervous system, reflex, reflex arcs, sympathetic nervous system, synapse, somatic nervous system system, spinal cord, central nervous system.

Nervous system controls, coordinates and regulates the coordinated work of all organ systems, the connection of the body with the external environment, maintaining the constancy of the composition of its internal environment. The nervous system is divided into central and peripheral . The central nervous system is made up of the brain and spinal cord. The peripheral nervous system consists of cranial and spinal nerves with their roots, branches and nerve endings, as well as nerve nodes or ganglia. The part of the peripheral nervous system that innervates skeletal muscles is called somatic nervous system . Another part of the peripheral nervous system, responsible for the innervation of internal organs, the circulatory and endocrine systems, the regulation of metabolic processes is called vegetative , or autonomic nervous system . The autonomic nervous system is divided into parasympathetic and sympathetic .

The structural and functional unit of the nervous system is the nerve cell - neuron . Its main properties are excitability and conductivity. Neurons consist of a body and processes. A long single process that transmits a nerve impulse from the body of a neuron to other nerve cells is called axon . The short processes along which the impulse is conducted to the body of the neuron are called dendrites. There may be one or more. Axons, uniting in bundles, form nerves.

neurons are interconnected synapses- the space between neighboring cells, in which the chemical transmission of a nerve impulse from one neuron to another takes place. Synapses can occur between the axon of one neuron and the body of another, between the axons and dendrites of neighboring neurons, between the processes of neurons of the same name.

Synaptic impulses are transmitted by neurotransmitters- biologically active substances - norepinephrine, acetylcholine and others. Molecules of mediators as a result of interaction with the cell membrane change its permeability for Ca ions + , TO + and Cl - . This leads to excitation of the neuron. The spread of excitation is associated with such a property of the nervous tissue as conductivity. There are synapses that inhibit the transmission of nerve impulses.

Depending on the function they perform, the following types are distinguished neurons:

– sensitive, or receptor whose bodies lie outside the CNS. They transmit an impulse from receptors to the central nervous system;

– intercalary that carry out the transfer of excitation from the sensitive to the executive neuron. These neurons lie within the CNS;

– executive, or motor, whose bodies are located in the central nervous system or in the sympathetic and parasympathetic nodes. They provide the transmission of impulses from the central nervous system to the working organs.

Nervous regulation carried out reflexively. A reflex is a response of the body to irritation that occurs with the participation of the nervous system. The nerve impulse that arose during irritation passes a certain path, called reflex arc. The simplest reflex arc consists of two neurons - sensitive and motor. Most reflex arcs are made up of several neurons.

reflex arc most often consists of the following units: receptor- a nerve ending that perceives irritation. Found in organs, muscles, skin, etc. Sensory neuron that transmits impulses to the CNS. An intercalary neuron lying in the central nervous system (brain or spinal cord), an executive (motor) neuron that transmits an impulse to an executive organ or gland.

Somatic reflex arcs carry out motor reflexes. Autonomic reflex arcs coordinate the work of internal organs.

The reflex reaction consists not only in excitation, but also in braking, i.e. in the delay or weakening of the resulting excitation. The relationship of excitation and inhibition ensures the coordinated work of the body.

EXAMPLES OF TASKS

Part A

A1. Nervous regulation is based on

1) electrochemical signal transmission

2) chemical signaling

3) mechanical signal propagation

4) chemical and mechanical signal transmission

A2. The central nervous system is made up of

1) brain

2) spinal cord

3) brain, spinal cord and nerves

4) brain and spinal cord

A3. The basic unit of nervous tissue is

1) nephron 2) axon 3) neuron 4) dendrite

A4. The site of transmission of a nerve impulse from neuron to neuron is called

1) neuron body 3) nerve ganglion

2) nerve synapse 4) intercalary neuron

A5. When the taste buds are stimulated, saliva begins to flow. This reaction is called

1) instinct 3) reflex

2) habit 4) skill

A6. The autonomic nervous system regulates activity

1) respiratory muscles 3) cardiac muscle

2) face muscles 4) limb muscles

A7. Which part of the reflex arc transmits a signal to the intercalary neuron

1) sensitive neuron 3) receptor

2) motor neuron 4) working organ

A8. The receptor is stimulated by a signal received from

1) sensitive neuron

2) intercalary neuron

3) motor neuron

4) external or internal stimulus

A9. Long processes of neurons unite in

1) nerve fibers 3) gray matter of the brain

2) reflex arcs 4) glial cells

A10. The mediator provides the transfer of excitation in the form

1) electrical signal

2) mechanical irritation

3) chemical signal

4) beep

A11. During lunch, the car alarm went off. Which of the following can happen at this moment in the cerebral cortex of this person

1) excitation in the visual center

2) inhibition in the digestive center

3) excitation in the digestive center

4) inhibition in the auditory center

A12. When burned, arousal occurs

1) in the bodies of executive neurons

2) in receptors

3) in any part of the nervous tissue

4) in intercalary neurons

A13. The function of the interneurons of the spinal cord is to

1) perception of irritation

2) conducting impulses from receptors to the central nervous system

3) conducting impulses from the central nervous system to organs

4) conducting impulses inside the central nervous system

Part B

IN 1. Select the links of the reflex arc that transmit impulses from the organ to the central nervous system

1) motor neuron 4) intercalary neuron

2) receptor 5) motor neuron

3) sensitive neuron 6) nerve center

IN 2. What are the functions of receptors?

1) perception of irritation from the external environment

2) conduction of impulses from the spinal cord to the brain

3) analysis of stimulation in the cerebral cortex

4) conversion of irritation into a nerve impulse

5) conducting an impulse along a nerve

6) receiving a signal from internal organs

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Reflexes underlie the nervous regulation of functions.

Reflex- this is a stereotypical (monotonous, repeating in the same way), response of the body to the action of stimuli with the mandatory participation of the central nervous system.

Principles of the reflex theory according to Pavlov

1 The principle of determinism. Each reflex has a reason.

2 The principle of structure. Each reflex has its own morphological substrate, its own reflex arc.

3. The principle of analysis and synthesis. Analysis - splitting into parts, synthesis - combining parts into a whole with a new quality. The implementation of the reflex is based on the morphological substance- reflex arc.

The reflex arc consists of 3 main parts:

afferent part of the reflex arc

2. central part of the reflex arc,

3. efferent part of the reflex arc

Afferent part- the simplest organization of the afferent part of the reflex arc is a sensitive neuron (located outside the central nervous system), while the axon of the sensitive neuron connects it to the central nervous system, and the dendrites of the sensitive neuron (represent sensitive nerves) carry information from the periphery to the body of the neuron. The main thing in the activity of the afferent neuron in the reflex arc is reception. It is due to reception that afferent neurons monitor the external environment, the internal environment, and carry information about this to the central nervous system. Some receptor cells are isolated into separate formations - sense organs. The main task of the afferent part of the reflex arc is to perceive information, i.e. perceive the action of the stimulus, and transmit this information to the central nervous system.

Efferent part presented somatic and autonomic nervous system. The neurons themselves, from which the somatic and autonomic nervous systems begin, lie within the CNS. Starting with subcortical formations and ending with the sacral spine. All cortical neurons DO NOT have a connection with the peripheral system.

For somatic nervous system a neuron that lies within the CNS gives off its axon, which reaches the innervated nervous system (peripheral organ).

autonomic nervous system- her 1st neuron lies within the CNS and its axon never reaches the peripheral organ. There are always 2 neurons. They form autonomic ganglia and only the axons of 2 neurons reach the peripheral organs. Properties of the efferent part (somatic, autonomic nervous system), see "Nerves. Conduction of nerve excitations along the nerves. Synapse. Transmission of excitation in the synapse."

The somatic and autonomic nervous systems, as efferents, have a common afferent system.

central part(see in the book) - intercalary neurons within the CNS are combined into nerve centers.

Exists anatomical and physiological concept of the nerve center.

Anatomical - the spatial association of individual neurons into a single whole is the nerve center.

Physiological - an ensemble of unity of neurons, united by responsibility for the distribution of one and the same function - the nerve center. From an anatomical point of view, a nerve is always a point, it is always a point space, from a physiological point of view, different parts of the nerve centers can be located on different floors of the central nervous system.

Neurons in nerve centers unite into nerve circuits chains create nervous networks. Exists two types of neural networks:

1. local nerve networks,

2. hierarchical neural networks.

local nerve networks- most of the neurons have a short axon and the network is formed from neurons of the same level. Local networks are characterized reverberation- Closed chains of neurons are often formed, through which excitation circulates with gradual attenuation.

Hierarchical networks- these are neurons united together, most of them have long axons that allow you to combine neurons located on different levels of the central nervous system in a chain of neurons. With the help of these networks, subordinate relationships are built in these branched chains of neurons. Hierarchical neural networks organize their activities on two principles: divergence, convergence. Divergence- this is when the input of information is one in the nerve center, and the output is multichannel. Convergence- when there are many information inputs, but only one output.

Properties of nerve centers:

1. nerve centers have a pronounced ability to summation excitations. Summation can be: temporal, spatial/cm. "Synapse"/,

2. irradiation the resulting excitation - the spread of excitation to adjacent neurons.

3. concentration excitation - contraction of excitation to one or more neurons.

4. induction- guidance of the opposite process. Induction happens: positive (when the process of excitation is induced), negative (when the process of inhibition is induced). Induction is divided into: simultaneous, consecutive. Simultaneous- at least two nerve centers are involved in it. In the first one, the process of inhibition or excitation first arises, and the opposite process leads to the neighboring center for the second time. consistent- always develops in the same center. This is such a phenomenon when one process in the center induces a directly opposite process (in the same center).

5. transformation- the ability of the nerve centers to convert the frequency and strength of the incoming excitation. Moreover, the nerve centers can work in a downward and upward mode.

6. occlusion(blockage) - the redundancy of incoming information can lead to blockage of the exit gate from the nerve center.

7. animation- nerve centers are able to multiply the effect.

8. spontaneous electrical activity.

9. aftereffect.

10.reverberation.

1 1. delay in time- occurs when the excitation passes through the nerve center. This is called the central delay of the reflex, it accounts for 1/3 of the total time of the latent period.

12. single destination principle- afferents can be different, internal information in the brain can come from different parts, but the answer will always be the same.

13. tone of nerve centers- some constant level of excitation. Most of the nerves have a pronounced tone at rest, i.e. they are excited partially at rest.

14. plastic nerve centers - their ability to rebuild when conditions of existence change,

15. High fatigue NC,

16. High sensitivity to neurotropic poisons.

17. D ominant. The ability, due to strong excitation, to dominate other nerve centers.

The central part of the reflex arc performs its functions due to the constant interactions of inhibition and excitation processes.