Introduction

1. Reflex theory and its basic principles

2. Reflex - a concept, its role and significance in the body

3. The reflex principle of building the nervous system. Feedback principle

Conclusion

Literature

Introduction

Human interaction with reality is carried out through the nervous system.

In humans, the nervous system consists of three sections: the central, peripheral and autonomic nervous systems. The nervous system functions as a single and integral system.

The complex, self-regulating activity of the human nervous system is carried out due to the reflex nature of this activity.

This paper will reveal the concept of "reflex", its role and significance in the body.

1. Reflex theory and its basic principles

The provisions of the reflex theory developed by I. M. Sechenov. I. P. Pavlov and developed by N. E. Vvedensky. A. A. Ukhtomsky. V. M. Bekhterev, P. K. Anokhin and other physiologists are the scientific and theoretical basis of Soviet physiology and psychology. These propositions find their creative development in the research of Soviet physiologists and psychologists.

The reflex theory, which recognizes the reflex essence of the activity of the nervous system, is based on three main principles:

1) the principle of materialistic determinism;

2) the principle of structure;

3) the principle of analysis and synthesis.

Principle of materialistic determinism means that each nervous process in the brain is determined (caused) by the action of certain stimuli.

Structural principle lies in the fact that the differences in the functions of different parts of the nervous system depend on the features of their structure, and the change in the structure of parts of the nervous system in the process of development is due to a change in functions. Thus, in animals that do not have a brain, the higher nervous activity is much more primitive than the higher nervous activity of animals that have a brain. In humans, in the course of historical development, the brain has reached especially complex structure and perfection that is associated with it labor activity and social conditions of life that require constant verbal communication.

Principle of analysis and synthesis is expressed as follows. When centripetal impulses enter the central nervous system, excitation occurs in some neurons, inhibition occurs in others, i.e., physiological analysis. The result is the distinction between specific objects and phenomena of reality and processes occurring inside the body.

At the same time, during the formation of a conditioned reflex, a temporary nervous connection (closure) is established between the two foci of excitation, which physiologically expresses synthesis. The conditioned reflex is the unity of analysis and synthesis.

2. Reflex - a concept, its role and significance in the body

Reflexes (from the Latin slot reflexus - reflected) are the body's responses to irritation of receptors. In the receptors, nerve impulses arise, which, through the sensory (centripetal) neurons, enter the central nervous system. There, the received information is processed by intercalary neurons, after which motor (centrifugal) neurons are excited and nerve impulses actuate the executive organs - muscles or glands. Intercalary neurons are called neurons, the bodies and processes of which do not go beyond the central nervous system. The path along which nerve impulses pass from the receptor to the executive organ is called the reflex arc.

Reflex actions are holistic actions aimed at satisfying a specific need for food, water, security, etc. They contribute to the survival of an individual or species as a whole. They are classified into food, water-producing, defensive, sexual, orienting, nest-building, etc. There are reflexes that establish a certain order (hierarchy) in a herd or flock, and territorial reflexes that determine the territory captured by one or another individual or flock.

There are positive reflexes, when the stimulus causes a certain activity, and negative, inhibitory, in which the activity stops. The latter, for example, include a passive-defensive reflex in animals, when they freeze at the appearance of a predator, an unfamiliar sound.

Reflexes play an exceptional role in maintaining constancy internal environment organism, its homeostasis. So, for example, when increasing blood pressure there is a reflex slowdown of cardiac activity and expansion of the lumen of the arteries, so the pressure decreases. With its strong fall, opposite reflexes arise, strengthening and speeding up the contractions of the heart and narrowing the lumen of the arteries, as a result, the pressure rises. It continuously fluctuates around a certain constant value, which is called the physiological constant. This value is genetically determined.

The famous Soviet physiologist P. K. Anokhin showed that the actions of animals and humans are determined by their needs. For example, the lack of water in the body is first replenished by internal reserves. There are reflexes that delay the loss of water in the kidneys, the absorption of water from the intestines increases, etc. If this does not lead to desired result, in the centers of the brain that regulate the flow of water, there is excitement and a feeling of thirst. This arousal causes goal-directed behavior, the search for water. Thanks to direct connections, nerve impulses from the brain to the executive organs are provided necessary actions(the animal finds and drinks water), and thanks to feedback, nerve impulses going in the opposite direction - from peripheral organs: oral cavity and stomach - to the brain, informs the latter about the results of the action. So, while drinking, the center of water saturation is excited, and when the thirst is satisfied, the corresponding center is inhibited. This is how the controlling function of the central nervous system is carried out.

A great achievement of physiology was the discovery by I. P. Pavlov conditioned reflexes.

Unconditioned reflexes are inborn, inherited by the body reactions to environmental influences. Unconditioned reflexes are characterized by constancy and do not depend on training and special conditions for their occurrence. For example, the body responds to pain irritation with a defensive reaction. There is a wide variety of unconditioned reflexes: defensive, food, orientation, sexual, etc.

The reactions underlying unconditioned reflexes in animals have been developed over millennia in the course of adaptation various kinds animals to the environment, in the process of struggle for existence. Gradually, under conditions of long evolution, the unconditioned reflex reactions necessary to satisfy biological needs and preserve the vital activity of the organism were fixed and inherited, and those of the unconditioned reflex reactions that lost their value for the life of the organism lost their expediency, on the contrary, disappeared, not recovering.

Under the influence of a constant change in the environment, more durable and perfect forms of animal response were required to ensure the adaptation of the organism to the changed conditions of life. In the process individual development in highly organized animals, a special kind of reflexes is formed, which IP Pavlov called conditional.

Conditioned reflexes acquired by an organism during its lifetime ensure the corresponding reaction of a living organism to changes in the environment and, on this basis, balance the organism with the environment. Unlike unconditioned reflexes, which are usually carried out by the lower parts of the central nervous system (spinal, medulla oblongata, subcortical nodes), conditioned reflexes in highly organized animals and in humans are carried out mainly by the higher part of the central nervous system (bark hemispheres brain).

The observation of the phenomenon of "mental secretion" in a dog helped IP Pavlov to discover the conditioned reflex. The animal, seeing food at a distance, intensively salivated even before the food was served. This fact has been interpreted in different ways. The essence of "mental secretion" was explained by IP Pavlov. He found that, firstly, in order for a dog to start salivating at the sight of meat, it had to see and eat it at least once before. And, secondly, any stimulus (for example, the type of food, a bell, a flashing light, etc.) can cause salivation, provided that the time of action of this stimulus and the time of feeding coincide. If, for example, feeding was constantly preceded by the knocking of a cup in which the food was located, then there always came a moment when the dog began to salivate just at one knock. Reactions that are caused by stimuli that were previously indifferent. I. P. Pavlov called conditioned reflex. The conditioned reflex, I. P. Pavlov noted, is a physiological phenomenon, since it is associated with the activity of the central nervous system, and at the same time, a psychological one, since it is a reflection in the brain of the specific properties of stimuli from outside world.

Conditioned reflexes in animals in the experiments of I. P. Pavlov were most often developed on the basis of an unconditioned food reflex, when food served as an unconditioned stimulus, and one of the stimuli (light, sound, etc.) indifferent (indifferent) to food performed the function of a conditioned stimulus. .).

There are natural conditioned stimuli, which serve as one of the signs of unconditioned stimuli (the smell of food, the squeak of a chicken for a chicken, which causes a parental conditioned reflex in it, the squeak of a mouse for a cat, etc.), and artificial conditioned stimuli that are completely unrelated to unconditioned reflex stimuli. (for example, a light bulb, to the light of which a salivary reflex was developed in a dog, the ringing of a gong, on which moose gather for feeding, etc.). However, any conditioned reflex has a signal value, and if the conditioned stimulus loses it, then the conditioned reflex gradually fades away.

Reflex activity provides communication of the body with the environment, allows you to adequately respond to external and internal changes and quickly protect yourself from external harmful air and respond to internal changes. Eat - find prey. To maintain the constancy of the parameters of the internal environment, to regulate these parameters.

Reflex arc and reflex act.

The material substrate of the reflex is the reflex arc, which is formed by a chain of neurons connected by synaptic connections. Through the reflex arc, nerve impulses from excited sensory receptors travel through the central nervous system to the cells of the executive tissues and organs.

The reflex arc consists of the following elements:

1. sensitive receptor- highly specialized formations that perceive and transform the energy of an external stimulus and transmit nerve impulses to the central structures along sensory nerves

2. sensory neuron- afferent neuron, the cat conducts a nerve impulse to the central nervous system and the set of sensory neurons is located outside the central nervous system

3. Intercalated/associative/interneurons- located in the CNS, receive information from the sensory neuron and transmit it to the efferent neuron - motor neuron / executive

4. Efferent neuron/motoneuron- receives information from the interneuron and transmits it to the effector/executive organ. The bodies of motoneurons are in the CNS, and the axons belong to the peripheral NS

5. Working body / effector- Muscles and glands. Therefore, all reflex responses can be reduced either to m-c contraction, or to secret allocation.

Excitation along the reflex arc due to synapses goes in one direction: from sensitive receptors through the central nervous system to the effector. The set of sensitive receptors, the stimulation of which causes a certain reflex is called receptive field of the reflex.

Reflex time- the time from the moment of action of the stimulus on sensitive receptors to the response from the side of the effector.

Depending on the number of synapses included in the reflex arc, there are:

1. Polysynaptic reflex arcs-consisting of 3 or more neurons

2. Monosynaptic consists of 1 synapse, when inf with feelings is transmitted to the motor. In humans, only tendon reflexes are monosynaptic - knee, plantar, Achilles reflex.

Reflex is a complex nervous process, it distinguishes 4 functional link:

1- Irritation of receptors and impulse conduction along afferent pathways of n. impulses in the central nervous system

2- Deployment nervous process in the central nervous system, i.e. in structures that are called nerve centers and central departments analyzers.

3- Conduction of a nerve impulse along efferent / descending pathways, which causes or regulates the function of an organ

Any reflex act should be evaluated depending on the achievement desired result(Whether the m-tsy were reduced enough to ensure the bending of the arm elbow joint?) Such an assessment is carried out on the basis of feedback: in the effector there are sensitive receptors, inf-I from which enters the central nervous system (in skeletal muscles are proprioceptors)

4- Carrying out afferent impulses from the own sensory receptors of a functioning organ in the central nervous system - feedback information. Such a connection allows to correct the organs, as it makes it possible to regulate the intensity and nature of the organ's activity. Therefore, with reflex p-tions, it is more correct to speak of a reflex ring, taking into account feedback. The reflex ring includes: a reflex arc and ways to receive feedback information.

If the result of the reflector of the district is not achieved, the implementation excitation switching to new afferent pathways.

Therefore, the number of afferent and efferent neurons correlates as 5 to 1. That is, the same reflex response can be observed to a variety of stimuli. Can use 1 and the same final path. i.e. motor neurons certain groups mts, and the afferent links of these reflexes differ.

Charles Sherrington formulated this pattern as the principle of a common final path.

In the absence of the 4th link of the reflex act / feedback, the normal functional activity of the organ becomes impossible, because without feedback mechanisms, without signals that provide the result of the performed action, it is impossible to correct the reactions of the body, which means adaptation to the environment.

Particular physiology of the NS

Physiology spinal cord

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The basis of the activity of the nervous system is reflexes (reflex acts). Reflex It is the body's response to an external or internal stimulus. Numerous reflex acts are divided into unconditional and conditional.

Unconditioned reflexes - These are congenital (inherited) reactions of the body to stimuli carried out with the participation of the spinal cord or brain stem.

Conditioned reflexes - these are temporary reactions of the body acquired on the basis of unconditioned reflexes, carried out with the obligatory participation of the cerebral cortex big brain and forming the basis of higher nervous activity. Higher nervous activity is characterized by complexity reflex actions. They are based not just on reactions to a certain stimulus, but on the assessment of numerous afferent signals from the outside world and the internal environment of the body that enter the brain through various sensory pathways (proprioceptive, pain, tactile, visual, auditory, olfactory, etc.), and evaluation of memory cues that store information about past experiences.

It should be noted that, starting to perform a particular type of activity, a person usually predicts its results, i.e. preliminarily forms an afferent representation, and then performs an action, which leads to the appearance of a result. The coincidence or discrepancy between the predicted and real results of the action affects the nature of the accompanying emotional reactions. In the first case they are positive, in the second they are negative.

The morphological basis of any reflex is reflex arc, represented by a chain of neurons that provide the perception of irritation, the transformation of the energy of irritation into a nerve impulse, the conduction of a nerve impulse to nerve centers, the processing of incoming information and the implementation of a response.

Depending on the complexity of the reflex act, simple and complex reflex arcs are distinguished. As a rule, for the implementation of unconditioned reflexes, simple reflex arcs are formed. Conditioned reflexes are characterized by multi-neuron complex reflex arcs (Fig. 1.5).

Rice. 1.5.

a - simple reflex arc: 1 - receptor (sensitive) neuron; 2 - associative (intercalary) neuron; 3 - effector (motor) neuron; b - complex reflex arc; 1 - afferent path; 2 - associative (intercalary) neuron; 3 - effector (motor) neuron; 4 - receptor (sensitive) neuron; 5 - efferent path; 6 - brain

There are three links in a simple reflex arc - afferent, intercalary (associative) and efferent. The afferent link is represented by a sensitive, or receptor, neuron, which is located in the sensitive node spinal nerve and is represented by pseudo-unipolar cells. One process departs from the body of a pseudo-unipolar cell. It soon divides into peripheral and central processes. The peripheral process begins with receptors on the periphery (in the skin, muscles, tendons, articular bags). The area of ​​localization of receptors, the irritation of which leads to the emergence of a certain reflex, is called the reflexogenic zone. Nerve impulses that have arisen as a result of irritation of the receptors move in a centripetal direction, first to the body of the pseudo-unipolar cell, and then along its central process to the spinal cord. The central process of the receptor neuron forms a synaptic ending on the dendrites of the associative (intercalary) neuron.

Associative neuron is an intercalary link of the reflex arc and is a small multipolar cell with a short axon. It receives a nerve impulse with its dendrites or directly on the surface of the body, conducts it along the axon and forms a synaptic ending on the effector neuron.

effector neuron - This is a large multipolar cell, the axon of which leaves the central nervous system and ends with effector endings in the tissues of the working organ (in the striated muscles).

The complication of reflex arcs occurs due to the insertion link. Associative neurons form numerous nuclei (nerve centers) within the spinal cord and brain. Nerve centers are groups of neurons united on the basis of morphofunctional features, carrying out not only the synaptic transmission of nerve impulses from one neuron to another, but also their certain processing.

A two-way connection is established between the nerve center and the working organ during the implementation of any reflex. Reaching the effectors located in the muscle or gland, nerve impulses cause a response to irritation. In this case, the working effect is accompanied by irritation of receptors located in the executive organ. As a result of this, a new stream of impulses enters the nerve center. The presence of feedback allows you to control the correct execution of commands coming from the nerve centers, and to make additional timely correction in the performance of the body's responses.

Man is by nature active. He is the creator and creator, regardless of what kind of work he does.

Activity is a social category. Animals can only live, which manifests itself as a biological adaptation of the body to the requirements of the environment. A person is characterized by a conscious isolation of himself from nature, knowledge of its laws and a conscious impact on it. A person as a person sets goals for himself, is aware of the motives that prompt him to be active.

The principle of the unity of consciousness and activity, formulated by Soviet psychologists, generalizes a number of theoretical propositions. The content of consciousness is primarily those objects or aspects of cognizable activity that are included in the activity. Thus, the content and structure of consciousness are associated with activity. Activity as the most important characteristic mental reflection personality, is laid down and realized in objective activity and then becomes the mental quality of a person. Being formed in activity, consciousness manifests itself in it. By answering and completing the task, the teacher judges the level of knowledge of the student. Analyzing the educational activity of a student, the teacher makes a conclusion about his abilities, about the features of thinking and memory. By deeds and deeds, the nature of the relationship, feelings, strong-willed and other qualities of the personality are determined. The subject of psychological study is personality in activity.

Any type of activity is associated with movements, regardless of whether it is the musculoskeletal movement of the hand when writing, when performing a labor operation by a machine operator, or the movement of the speech apparatus when pronouncing words. There is movement physiological function living organism. Motor, or motor, function in humans appears very early. The first movements are observed during the intrauterine period of development, in the embryo. The newborn screams and makes chaotic movements with his hands and feet, he also has congenital complexes of complex movements; for example, sucking, grasping reflexes.

The congenital movements of an infant are not objectively directed and are stereotyped. As studies in childhood psychology show, accidental contact of an irritant with the surface of the palm of a newborn causes a stereotypical grasping movement. This is the initial unconditionally reflex connection between sensation and movement without reflecting the specifics of the influencing object. Significant changes in the nature of the grasping reflex occur at the age of 2.5 to 4 months. They are caused by the development of the senses, primarily vision and touch, as well as the improvement of motor skills and motor sensations. Prolonged contact with the object, carried out in a grasping reflex, occurs under the control of vision. Due to this, a system of visual-motor connections is formed based on tactile reinforcement. The grasping reflex disintegrates, giving way to conditioned reflex movements corresponding to the characteristics of the object.

On a physiological basis, all human movements can be divided into two groups: congenital (unconditioned reflex) and acquired (conditioned reflex). The vast majority of movements, including even such an elementary act common with animals as movement in space, a person acquires in life experience, that is, most of his movements are conditioned reflex. Only a very small number of movements (shouting, blinking) are innate. The motor development of the child is associated with the transformation of the unconditioned reflex regulation of movements into a system of conditioned reflex connections.

Anatomical and physiological mechanism of reflex activity

The main mechanism of nervous activity, both in the lowest and in the most complex organisms, is the reflex. A reflex is the response of the body to irritations of the external or internal environment. Reflexes differ in the following features: they always begin with a nervous excitation caused by some stimulus in one or another receptor, and end with a certain reaction of the body (for example, movement or secretion).

Reflex activity is a complex analyzing and synthesizing work of the cerebral cortex, the essence of which is the differentiation of numerous stimuli and the establishment of various connections between them.

The analysis of stimuli is performed by complex nerve analyzer organs. Each analyzer consists of three parts:

1) peripheral perceiving organ (receptor);

2) conductive afferent, i.e. the centripetal pathway, along which nervous excitation is transmitted from the periphery to the center;

3) cortical part of the analyzer (central link).

The transmission of nervous excitation from receptors first to the central parts of the nervous system, and then from them along the efferent, i.e. centrifugal, paths back to the receptors for the response that takes place during the reflex, is carried out along the reflex arc. The reflex arc (reflex ring) consists of a receptor, an afferent nerve, a central link, an efferent nerve, and an effector (muscle or gland).

The initial analysis of stimuli takes place in the receptors and in the lower parts of the brain. It has an elementary character and is determined by the degree of perfection of one or another receptor. The highest and most subtle analysis of stimuli is carried out by the cortex of the cerebral hemispheres, which is a combination of the brain endings of all analyzers.

In the course of reflex activity, the process of differential inhibition is also carried out, during which excitations caused by unreinforced conditioned stimuli, gradually fade away, but excitations remain, strictly corresponding to the main, reinforced conditioned stimulus. Thanks to differential inhibition, a very fine differentiation of stimuli is achieved. Because of this, the formation of conditioned reflexes to complex stimuli is possible.

In this case, the conditioned reflex is caused only by the action of the complex of stimuli as a whole and is not caused by the action of any one of the stimuli included in the complex.



CONDITIONAL REFLECTOR ACTIVITY OF THE ORGANISM

Reflex. Reflex arc. Types of reflexes

The main form of nervous activity is the reflex. Reflex - a causally determined reaction of the body to changes in the external or internal environment, carried out with the participation of the central nervous system in response to irritation of receptors. This is how the emergence, change or cessation of any activity of the body occurs.

Reflex arcs can be simple or complex. A simple reflex arc consists of two neurons - a perceiving and an effector, between which there is one synapse.

An example of a simple reflex arc is the tendon reflex arcs, such as the patellar reflex arc.

The reflex arcs of most reflexes include not two, but a larger number of neurons: receptor, one or more intercalary and effector. Such reflex arcs are called complex, multi-neuronal.

It has now been established that during the response of the effector, numerous nerve endings present in the working organ are excited. Nerve impulses now from the effector again enter the central nervous system and inform it about the correct response of the working organ. Thus, the reflex arcs are not open, but ring formations.

Reflexes are very diverse. They can be classified according to a number of criteria: 1) biological significance, (food, defensive, sexual);

2) depending on the type of irritated receptors:

exteroceptive, interoceptive and proprioceptive;

3) by the nature of the response: motor or motor (executive organ - muscle), secretory (effector - iron), vasomotor (constriction or expansion of blood vessels).

All reflexes of the whole organism can be divided into two large groups: unconditioned and conditioned.

From the receptors, nerve impulses travel along afferent pathways to the nerve centers. It is necessary to distinguish between the anatomical and physiological understanding of the nerve center.

Nerve center from an anatomical point of view - a set of neurons located in a specific section of the central nervous system. Due to the work of such a nerve center, a simple reflex activity is carried out, for example, a knee jerk. The nerve center of this reflex is located in lumbar spinal cord (II–IV segments):

The nerve center from a physiological point of view is a complex functional combination of several anatomical nerve centers located on different levels central nervous system and causing the most complex reflex acts due to their activity. For example, many organs (glands, muscles, blood and lymph vessels, etc.) are involved in the implementation of food reactions. The activity of these organs is regulated by nerve impulses coming from nerve centers located in various parts of the central nervous system. A. A. Ukhtomsky called these functional associations “constellations” of nerve centers.

Physiological properties of nerve centers. Nerve centers have a number of characteristic functional properties that depend on the presence of synapses and a large number of neurons that make up them. The main properties of the nerve centers are:

1) unilateral excitation;

2) delay in excitation;

3) summation of excitations;

4) transformation of the rhythm of excitations;

5) reflex aftereffect;

6) fast fatigue.

Unilateral conduction of excitation in the central nervous system due to the presence of synapses in the nerve centers, in which the transmission of excitation is possible only in one direction - from the nerve ending that releases the mediator to the postsynaptic membrane.

The delay in the conduction of excitation in the nerve centers is also associated with the presence of a large number of synapses. The release of the mediator, its diffusion through the synaptic cleft, and the excitation of the postsynaptic membrane require more time than the propagation of excitation along the nerve fiber.

The summation of excitations in the nerve centers occurs either when weak but repetitive (rhythmic) stimuli are applied, or when several subthreshold stimuli are applied simultaneously. The mechanism of this phenomenon is associated with the accumulation of a mediator on the postsynaptic membrane and an increase in the excitability of the cells of the nerve center. An example of the summation of excitation is the sneeze reflex. This reflex occurs only with prolonged irritation of the receptors of the nasal mucosa. For the first time, the phenomenon of summation of excitations in the nerve centers was described by I. M. Sechenov in 1863.

The transformation of the rhythm of excitations lies in the fact that the central nervous system responds to any rhythm of stimulation, even slow, with a volley of impulses. The frequency of excitations coming from the nerve centers to the periphery to the working body ranges from 50 to 200 per second. This feature of the central nervous system explains the fact that all contractions skeletal muscle in the body are tetanic.

Reflex acts end not simultaneously with the cessation of the stimulus that caused them, but after a certain, sometimes relatively long, period. This phenomenon is called the reflex aftereffect.

Two mechanisms responsible for the aftereffect have been established. or short term memory. The first is due to the fact that excitation in nerve cells does not disappear immediately after the cessation of irritation. For some time (hundredths of a second), nerve cells continue to give rhythmic discharges of impulses. This mechanism can cause only a relatively short aftereffect. The second mechanism is the result of the circulation of nerve impulses through closed neural circuits of the nerve center and provides a longer aftereffect.

The excitation of one of the neurons is transmitted to another, and along the branches of its axon it returns again to the first nerve cell. This is also called reverberation of signals. The circulation of nerve impulses in the nerve center will continue until one of the synapses becomes tired or the activity of neurons is suspended by the arrival of inhibitory impulses. Most often, not one, but many synapses of the excitation profile from the perceived one are involved in this process, and this area remains excited for a long time. This is very important point. With each act of perception in the brain, there are such centers of memory about the perceived, which can accumulate more and more during the day. Consciousness can leave this area and this picture will not be perceived, but it continues to exist, and if consciousness returns here, it will "remember" it. This leads not only to general exhaustion, but, being summed up by boundaries, makes it difficult to distinguish between images. During sleep, general inhibition extinguishes these foci.

Nerve centers are easily fatigued, in contrast to nerve fibers. With prolonged stimulation of afferent nerve fibers, fatigue of the nerve center is manifested by a gradual decrease, and then a complete cessation of the reflex response.

This feature of the nerve centers is proved as follows. After the cessation of muscle contraction in response to irritation of the afferent nerves, they begin to irritate efferent fibers that innervates the muscle. In this case, the muscle contracts again. Consequently, fatigue did not develop in the afferent pathways, but in the nerve center.

Reflex tone of nerve centers. In a state of relative rest, without causing additional irritation, discharges of nerve impulses arrive from the nerve centers to the periphery to the corresponding organs and tissues. At rest, the frequency of discharges and the number of simultaneously working neurons are very small. Rare impulses, continuously coming from the nerve centers, determine the tone (moderate tension) of the skeletal muscles, smooth muscles of the intestines and blood vessels. Such constant excitation of the nerve centers is called the tone of the nerve centers. It is supported by afferent impulses continuously coming from receptors (especially proprioreceptors) and various humoral influences (hormones, CO2, etc.).

Inhibition (as well as excitation) - active process. Inhibition occurs as a result of complex physicochemical changes in tissues, but outwardly this process is manifested by a weakening of the function of any organ.

In 1862, classical experiments were carried out by the founder of Russian physiology, I. M. Sechenov, called "central inhibition." I. M. Sechenov placed a crystal of sodium chloride ( table salt) and observed the inhibition of spinal reflexes. After elimination of the stimulus, the reflex activity of the spinal cord was restored.

The results of this experiment allowed I. M. Sechenov to conclude that in the central nervous system, along with the process of excitation, an inhibition process develops, which is capable of inhibiting the reflex acts of the body.

Currently, it is customary to distinguish two forms of inhibition: primary and secondary.

For the occurrence of primary inhibition, the presence of special inhibitory structures (inhibitory neurons and inhibitory synapses) is necessary. In this case, inhibition occurs primarily without prior excitation.

Examples of primary inhibition are pre- and postsynaptic inhibition. Presynaptic inhibition develops in axo-axonal synapses formed at the presynaptic endings of a neuron. Presynaptic inhibition is based on the development of a slow and prolonged depolarization of the presynaptic ending, which leads to a decrease or blockade of further conduction of excitation. Post-synaptic inhibition is associated with hyperpolarization of the postsynaptic membrane under the influence of mediators that are released during excitation of inhibitory neurons.

Primary inhibition plays an important role in limiting the flow of nerve impulses to effector neurons, which is essential in coordinating work. various departments central nervous system.

No special braking structures are required for the occurrence of secondary inhibition. It develops as a result of a change in the functional activity of ordinary excitable neurons.

The value of the braking process. Inhibition, along with excitation, takes an active part in the adaptation of the organism to the environment; Braking plays important role in the formation of conditioned reflexes: frees the central nervous system from processing less significant information; provides coordination of reflex reactions, in particular, a motor act. Inhibition limits the spread of excitation to other nervous structures, preventing disruption of their normal functioning, that is, inhibition performs a protective function, protecting the nerve centers from fatigue and exhaustion. Inhibition ensures the extinction of an undesirable, unsuccessful result of an action, and excitation enhances the desired one. This is ensured by the intervention of the system, which determines the importance of the result of the action for the organism.

The coordinated manifestation of individual reflexes that ensure the implementation of integral working acts is called coordination.

The phenomenon of coordination plays an important role in the activity of the motor apparatus. The coordination of such motor acts as walking or running is provided by the interconnected work of the nerve centers.

Due to the coordinated work of the nerve centers, the body is perfectly adapted to the conditions of existence.

Principles of coordination in the activity of the central nervous system

This happens not only due to the activity of the motor apparatus, but also due to changes in the vegetative functions of the body (the processes of respiration, blood circulation, digestion, metabolism, etc.).

A number of general patterns have been established - the principles of coordination: 1) the principle of convergence; 2) the principle of irradiation of excitation; 3) the principle of reciprocity; 4) the principle of sequential change of excitation by inhibition and inhibition by excitation; 5) the phenomenon of "recoil"; 6) chain and rhythmic reflexes; 7) the principle of a common final path; 8) the principle of feedback; 9) the principle of dominance.

The principle of convergence. This principle was established by the English physiologist Sherrington. Impulses coming to the central nervous system through different afferent fibers can converge (convert) to the same intercalary and effector neurons. The convergence of nerve impulses is explained by the fact that there are several times more afferent neurons than effector ones. Therefore, afferent neurons form numerous synapses on the bodies and dendrites of effector and intercalary neurons.

The principle of irradiation. Impulses entering the central nervous system with strong and prolonged irritation of the receptors cause excitation not only of this reflex center but also other nerve centers. This spread of excitation in the central nervous system is called irradiation. The process of irradiation is associated with the presence in the central nervous system of numerous branches of axons and especially dendrites. nerve cells and chains of intercalary neurons that connect various nerve centers with each other.

The principle of reciprocity(conjugation). This phenomenon was studied by I. M. Sechenov, N. E. Vvedensky, Sherrington. Its essence lies in the fact that when some nerve centers are excited, the activity of others can be inhibited. The principle of reciprocity was shown in relation to the nerve centers of antagonists of the flexor and extensor muscles of the limbs. It manifests itself most clearly in animals with a removed brain and preserved spinal cord (spinal animal). If the skin of a limb is irritated in a spinal animal (cat), a flexion reflex of this limb is noted, and on the opposite side at this time an extension reflex is observed. The phenomena described are related to the fact that when the flexion center of one limb is excited, reciprocal inhibition of the extension center of the same limb occurs. On the symmetrical side, there are reverse relationships: the extensor center is excited and the flexor center is inhibited. Walking is possible only with such mutually combined (reciprocal) innervation.

The reciprocal relationships of the centers of the brain determine the ability of a person to master complex labor processes and no less complex special movements that occur during swimming, acrobatic exercises, and so on.

The principle of a common final path. This principle is associated with the peculiarity of the structure of the central nervous system. This feature, as already mentioned, consists in the fact that there are several times more afferent neurons than effector neurons, as a result of which various afferent impulses converge to common output paths. The quantitative relationships between neurons can be schematically represented as a funnel: excitation flows into the central nervous system through a wide bell (afferent neurons) and flows out of it through a narrow tube (effector neurons). Common paths can be not only final effector neurons, but also intercalary ones.

Feedback principle. This principle was studied by I. M. Sechenov, Sherrington, P. K. Anokhin and a number of other researchers. With reflex contraction of skeletal muscles, proprioreceptors are excited. From proprioreceptors, nerve impulses again enter the central nervous system. This controls the accuracy of the movements made. Similar afferent impulses arising in the body as a result of the reflex activity of organs and tissues (effectors) are called secondary afferent impulses or "feedback".

Feedback can be either positive or negative. Positive feedback enhances reflex reactions, negative feedback suppresses them.

The principle of dominance was formulated by A. A. Ukhtomsky. This principle plays an important role in the coordinated work of the nerve centers. Dom and nta is a temporarily dominant focus of excitation in the central nervous system, which determines the nature of the body's response to external and internal stimuli. In fact, this is a neurophysiological manifestation of the most general, dominant emotion.

The dominant focus of excitation is characterized by the following main properties: 1) increased excitability; 2) persistence of arousal; 3) the ability to sum up excitation; 4) inertia - the dominant in the form of traces of excitation can persist for a long time even after the cessation of the irritation that caused it.

The dominant focus of excitation is able to attract (attract) nerve impulses to itself from other nerve centers that are less excited in this moment. Due to these impulses, the activity of the dominant increases even more, and the activity of other nerve centers is suppressed.

Dominants can be of exogenous and endogenous origin. Exogenous dominant occurs under the influence of environmental factors. For example, when reading interesting book a person may not hear the music playing on the radio at this time.

The endogenous dominant arises under the influence of factors of the internal environment of the body, mainly hormones and other physiologically active substances. For example, when lowering the content nutrients in the blood, especially glucose, there is an excitation of the food center, which is one of the reasons for the food installation of the organism of animals and humans.

The dominant can be inert (persistent), and for its destruction it is necessary to create a new, more powerful focus of excitation.

The dominant underlies the coordination activity of the organism, ensuring the behavior of humans and animals in the environment, emotional states, reactions of attention. The formation of conditioned reflexes and their inhibition is also associated with the presence of a dominant focus of excitation.