The activity of the nervous system is carried out according to the reflex principle. Activities of the nervous system

The main and specific manifestation of the activity of the nervous system is the reflex principle. This is the body’s ability to respond to external or internal stimulation with a motor or secretory response. The foundations of the doctrine of the reflex activity of the body were laid by the French scientist Rene Descartes (1596-1650). Of greatest importance were his ideas about the reflex mechanism of the relationship of the organism with the environment. The term “reflex” itself was introduced much later - mainly after the publication of the works of the outstanding Czech anatomist and physiologist G. Prohaska (1749-1820).

A reflex is a natural reaction of the body in response to irritation of receptors, which is carried out by a reflex arc with the participation of the central nervous system. This is an adaptive reaction of the body in response to changes in the internal or environmental environment. Reflex reactions ensure the integrity of the body and the constancy of its internal environment; the reflex arc is the basic unit of integrative reflex activity.

A significant contribution to the development of reflex theory was made by I.M. Sechenov (1829-1905). He was the first to use the reflex principle to study physiological mechanisms mental processes. In the work “Reflexes of the Brain” (1863) I.M. Sechenov convincingly proved that the mental activity of humans and animals is carried out according to the mechanism of reflex reactions that occur in the brain, including the most complex of them - the formation of behavior and thinking. Based on his research, he concluded that all acts of conscious and unconscious life are reflexive. Reflex theory of I.M. Sechenov served as the basis on which the teaching of I.P. arose. Pavlova (1849-1936) about higher nervous activity. The method of conditioned reflexes he developed expanded the scientific understanding of the role of the cerebral cortex as a material substrate of the psyche. I.P. Pavlov formulated a reflex theory of brain function, which is based on three principles: causality, structure, unity of analysis and synthesis. P.K. Anokhin (1898-1974) proved the importance of feedback in the reflex activity of the body. Its essence is that during the implementation of any reflex act, the process is not limited only to the effector, but is accompanied by excitation of the receptors of the working organ, from which information about the consequences of the action arrives through afferent pathways to the central nervous system. Ideas about a “reflex ring” and “feedback” appeared.

Reflex mechanisms play a significant role in the behavior of living organisms, ensuring their adequate response to environmental signals. For animals, reality is signaled almost exclusively by stimuli. This is the first signal system of reality, common to humans and animals. I.P. Pavlov proved that for humans, unlike animals, the object of reflection is not only the environment, but also social factors. Therefore, for him, the second signal system acquires decisive importance - the word as a signal of the first signals.

The conditioned reflex underlies the higher nervous activity of humans and animals. It is always included as an essential component in the most complex manifestations of behavior. However, not all forms of behavior of a living organism can be explained from the point of view of the reflex theory, which reveals only the mechanisms of action. The reflex principle does not answer the question of the appropriateness of human and animal behavior and does not take into account the result of the action.

Therefore, over the past decades, on the basis of reflexive ideas, a concept has been formed regarding the leading role of needs as driving force behavior of humans and animals. The presence of needs is a necessary prerequisite for any activity. The activity of the body acquires a certain direction only if there is a goal that meets this need. Each behavioral act is preceded by needs that arose in the process of phylogenetic development under the influence of environmental conditions. That is why the behavior of a living organism is determined not so much by a reaction to external influences, but by the need to implement the intended program, plan, aimed at satisfying one or another need of a person or animal.

PC. Anokhin (1955) developed the theory of functional systems, which provides a systematic approach to the study of the mechanisms of the brain, in particular, the development of problems of the structural and functional basis of behavior, the physiology of motivation and emotions. The essence of the concept is that the brain can not only adequately respond to external stimuli, but also foresee the future, actively make plans for its behavior and implement them. The theory of functional systems does not exclude the method of conditioned reflexes from the sphere of higher nervous activity and does not replace it with something else. It makes it possible to delve deeper into the physiological essence of the reflex. Instead of the physiology of individual organs or brain structures, the systems approach considers the activity of the organism as a whole. For any behavioral act of a person or animal, an organization of all brain structures is needed that will provide the desired final result. So, in the theory of functional systems, the central place is occupied by the useful result of an action. Actually, the factors that are the basis for achieving a goal are formed according to the type of versatile reflex processes.

One of the important mechanisms of the central nervous system is the principle of integration. Thanks to the integration of somatic and autonomic functions, which is carried out by the cerebral cortex through the structures of the limbic-reticular complex, various adaptive reactions and behavioral acts are realized. Highest level Integrating functions in humans are the frontal cortex.

The principle of dominance, developed by O. O. Ukhtomsky (1875-1942), plays an important role in the mental activity of humans and animals. Dominant (from the Latin dominari to dominate) is a superior excitation in the central nervous system, which is formed under the influence of stimuli from the surrounding or internal environment and at a certain moment subordinates the activity of other centers.

The brain with its highest section - the cerebral cortex - is a complex self-regulatory system built on the interaction of excitatory and inhibitory processes. The principle of self-regulation is carried out at different levels of analyzer systems - from the cortical sections to the level of receptors with the constant subordination of the lower parts of the nervous system to the higher ones.

When studying the principles of functioning of the nervous system, it is not without reason that the brain is compared to an electronic computer. As is known, the basis of the operation of cybernetic equipment is the reception, transmission, processing and storage of information (memory) with its further reproduction. For transmission, information must be encoded, and for reproduction, it must be decoded. Using cybernetic concepts, we can consider that the analyzer receives, transmits, processes and, possibly, stores information. Its decoding is carried out in the cortical sections. This is probably enough to make it possible to try to compare the brain with a computer. At the same time, one cannot identify the work of the brain with a computer: “... the brain is the most capricious machine in the world. Let us be modest and careful with our conclusions” (I.M. Sechenov, 1863). A computer is a machine and nothing more. All cybernetic devices operate on the principle of electrical or electronic interaction, and in the brain, which is created by evolutionary development In addition, complex biochemical and bioelectric processes occur. They can only be carried out in living tissue. The brain, unlike electronic systems, does not function on an all-or-nothing basis, but takes into account a great many gradations between these two extremes. These gradations are due not to electronic, but to biochemical processes. This is a significant difference between the physical and the biological. The brain has qualities that go beyond those of a computing machine. It should be added that the behavioral reactions of the body are largely determined by intercellular interactions in the central nervous system. One neuron typically receives branches from hundreds or thousands of other neurons, and it in turn branches off into hundreds or thousands of other neurons. No one can say how many synapses there are in the brain, but the number 10 14 (one hundred trillion) does not seem incredible (D. Hubel, 1982). The computer holds significantly fewer elements. The functioning of the brain and the vital activity of the body are carried out under specific environmental conditions. Therefore, the satisfaction of certain needs can be achieved provided that this activity is adequate to the existing external environmental conditions.

For the convenience of studying the basic patterns of functioning, the brain is divided into three main blocks, each of which performs its own specific functions.

The first block is the phylogenetically ancient structures of the limbic-reticular complex, which are located in the stem and deep parts of the brain. They include the cingulate gyrus, seahorse (hippocampus), papillary body, anterior nuclei of the thalamus, hypothalamus, and reticular formation. They provide regulation of vital functions - breathing, blood circulation, metabolism, as well as general tone. Regarding behavioral acts, these formations take part in the regulation of functions aimed at ensuring eating and sexual behavior, the processes of preserving the species, in the regulation of systems that ensure sleep and wakefulness, emotional activity, and memory processes.

The second block is a set of formations located behind the central sulcus: the somatosensory, visual and auditory areas of the cerebral cortex. Their main functions are: receiving, processing and storing information.

The neurons of the system, which are located predominantly anterior to the central sulcus and are associated with effector functions and the implementation of motor programs, constitute the third block.

However, it should be recognized that it is impossible to draw a clear boundary between the sensory and motor structures of the brain. The postcentral gyrus, which is a sensitive projection zone, is closely interconnected with the precentral motor zone, forming a single sensorimotor field. Therefore, it is necessary to clearly understand that this or that human activity requires the simultaneous participation of all parts of the nervous system. Moreover, the system as a whole performs functions that go beyond the functions inherent in each of these blocks.

The interaction of nerve cells forms the basis for the purposeful activity of the nervous system and, above all, the implementation of reflex acts. Thus, nervous regulation is reflexive in nature.

Reflex call the body's response to receptor irritation, carried out through the central nervous system (CNS). The basic principles of the reflex principle of the central nervous system have been developed over two and a half centuries. Scientists identify five stages in the development of this concept.

First stage. Associated with the formation in the 16th century of the foundations for understanding the reflex principle of the central nervous system. The principle of reflex (reflective) activity of the nervous system was put forward in the 17th century by the French philosopher and mathematician Rene Descartes, who believed that all things and phenomena can be explained by natural science. This initial position allowed R. Descartes to formulate two important provisions of the reflex theory:

1) the activity of the body under external influence is reflected (later it began to be called reflex - from the Latin reflexus - reflected);

2) the response to irritation is carried out using the nervous system.

According to the theory of R. Descartes, nerves are tubes through which animal spirits and material particles of an unknown nature move at great speed. They travel along the nerves to the muscle, which as a result swells (contracts).

Second stage. Associated with the experimental substantiation of materialistic ideas about the reflex (XV11 - XV111 centuries). In particular, it was found that the reflex reaction can be carried out on one frog metamere ( metame p - a segment of the spinal cord associated with a “piece of body”). A significant contribution to the development of ideas about the reflex activity of the nervous system was made by the Czech physiologist of the 18th century I. Prochazka, who proceeded from the recognition of the unity of the body and the environment, and also asserted the leading role of the nervous system in the regulation of body functions. It was I. Prokhazka who proposed the very term “reflex”. In addition, he introduced the law of force into physiology (increasing the strength of a stimulus increases the strength of the reflex reaction of the body; there are not only external but also internal stimuli); first described the classical reflex arc. During this time period, scientists, as a result of clinical experimental studies, established the role of the posterior (sensitive) and anterior (motor) roots of the spinal cord (Bell-Magendie law). Active reflex activity (in particular, segmental reflexes) is studied by Ch. Sherrington. As a result of his scientific research, the scientist describes the principle of afferent innervation of antagonist muscles, introduces the concept of “synapse”, the principle of a common nerve pathway, and the concept of the integrative activity of the nervous system.

Third stage. Materialistic ideas about mental activity are being established (I.M. Sechenov, 1960s). Observing the development of children, the scientist comes to the conclusion that the principle of reflex underlies the formation of mental activity. He expressed this statement in the following phrase: “All acts of conscious and unconscious life, according to the method of origin, are reflexes.” When studying reflexes, he substantiated the adaptive nature of the variability of the reflex, discovered the mechanism of inhibition of reflexes, as well as the mechanism of summation of excitation in the central nervous system.

Fourth stage. Associated with the development of the fundamentals of the doctrine of higher nervous activity (research by I.P. Pavlov, early twentieth century). I.P. Pavlov discovered conditioned reflexes and used them as an objective method in the study of mental activity (higher nervous activity). Scientists formulated three basic principles of reflex theory:

1. The principle of determinism (principle of causality), according to which any reflex reaction is causally determined. I.P. Pavlov argued: “There is no action without a reason.” Every activity of the body, every act of nervous activity is caused by a specific cause, influence from the external world or the internal environment of the body. The appropriateness of the reaction is determined by the specificity of the stimulus, the sensitivity of the body to them (stimuli).

2. The principle of structure. Its essence lies in the fact that the reflex reaction is carried out using certain structures. The more structures and structural elements involved in this reaction, the more perfect it is. There are no processes in the brain that do not have a material basis. Each physiological act of nervous activity is confined to a specific structure.

3. The principle of unity of the processes of analysis and synthesis as part of a reflex reaction. The nervous system analyzes, i.e. distinguishes, with the help of receptors, all acting external and internal stimuli and, based on this analysis, forms a holistic response - synthesis. Analysis and synthesis of both incoming information and responses occurs continuously in the brain. As a result, the body extracts from the environment useful information, processes it, records it in memory and forms response actions in accordance with circumstances and needs.

Fifth stage. Characterized by the creation of the doctrine of functional systems (research by P.K. Anokhin, mid-twentieth century). A functional system is a dynamic set of various organs and tissues that is formed to achieve a useful (adaptive) result. A useful result is maintaining the constancy of the internal environment of the body through the regulation of the functions of internal organs and behavioral somatic regulation (for example, the search and consumption of water when there is a lack of water in the body and thirst arises - a biological need). Satisfying a social need (achieving high results in educational activities) can also be a useful result.

Studying the reflex basis of the vital activity of living organisms, scientists came to the conclusion that the basic ones are innate (unconditioned) reflexes, since these reflexes, formed over millions of years of evolution, are the same for all representatives of a particular species of animal organism and depend little on the situational conditions of existence of that organism. or another specific representative of a given animal species. With a sharp change in environmental conditions, an unconditioned reflex can lead to the death of the organism.

Unconditioned reflexes– the body’s response to irritation of sensory receptors, carried out using the nervous system. I.P. Pavlov identified, first of all, unconditioned reflexes aimed at self-preservation of the body (the main ones here are food, defensive, orientation and some others). These reflexes make up large groups various innate reactions.

Unconditioned reflex activity was studied by P.V. Somonov. According to the scientist, the development of each sphere of the environment corresponds to three different classes unconditioned reflexes:

· vital unconditioned reflexes that ensure individual and species preservation of the body (food, drink, sleep regulation, defensive and orientation, energy saving reflex, etc.). The criteria for these reflexes are: the physical death of an individual as a result of dissatisfaction of the corresponding need, the implementation of an unconditioned reflex without the participation of another individual of the same species;

· role-playing (zoosocial). They can be realized only through interaction with other individuals of their species. These reflexes underlie territorial, parental, etc. behavior. In addition, they are of great importance for the phenomenon of emotional resonance, “empathy” and the formation of a group hierarchy, where each individual invariably plays one role or another (mating partner, parent or cub, owner of the territory or alien, leader or follower, etc.). d.);

· unconditioned reflexes of self-development. They are focused on mastering new spatio-temporal environments and are oriented towards the future. These include exploratory behavior, the unconditioned reflex of resistance (freedom), imitation (imitative) and play.

Scientists also include the orienting reflex among the unconditioned reflexes. Orienting reflex- unconditional reflex involuntary sensory attention, accompanied by an increase in muscle tone, caused by an unexpected or new stimulus for the body. Scientists often call this reaction a reflex of wariness, anxiety, surprise, and I.P. Pavlov defined it as a reflex “what is this?” The orientation reflex is characterized by the manifestation of a whole complex of reactions. Scientists distinguish three phases in the development of this reflex.

First phase. Characterized by cessation of current activity and fixation of posture. According to P.V. Simonov, this is a general (preventive) inhibition that occurs upon the appearance of any extraneous stimulus with an unknown signal value.

Second phase. It begins when the “stop reaction” state turns into an activation reaction. At this phase, the entire body is transferred to a state of reflex readiness for a possible meeting with emergency, which manifests itself in a general increase in the tone of all skeletal muscles. At this phase, the orienting reflex manifests itself in the form of a multicomponent reaction, including turning the head and eyes in the direction of the stimulus.

Third phase. It begins with fixing the stimulus field to develop the process of differentiated analysis of external signals and make a decision about the body’s response.

The multicomponent composition of the orientation reflex indicates its complex morphofunctional organization.

The orienting reflex is part of the structure of orienting behavior (orienting-exploratory activity), which is especially pronounced in a new environment. Research activity here can be aimed both at mastering novelty, satisfying curiosity, and at searching for a stimulus, an object that can satisfy this need. In addition, the orienting reflex is also aimed at determining the “significance” of the stimulus. At the same time, there is an increase in the sensitivity of the analyzers, which makes it easier to perceive the stimuli affecting the body and determine their meaning.

The mechanism for the implementation of the orientation reflex is the result of a dynamic interaction between many different formations of specific and nonspecific systems of the central nervous system. Thus, the general activation phase is associated mainly with the activation of the stem reticular formation and generalized excitation of the cortex. In the development of the stimulus analysis phase, the leading place is occupied by cortical-limbic-thalamic integration. In this case, the hippocampus plays an important role. This ensures the specialized processes of analyzing the “novelty” and “significance” of a stimulus.

Along with unconditioned reflexes that can be attributed to lower nervous activity, in higher animals and humans, on the basis of this lower nervous activity, new mechanisms of adaptation to constantly changing environmental conditions have been formed - higher nervous activity. With its help, and more specifically, with the help of conditioned reflexes, these living organisms acquired the ability to respond not only to the direct influence of biologically significant agents (food, defensive, etc.), but also to their remote signs.

At the turn of the 19th and 20th centuries, the famous Russian physiologist I.P. Pavlov, for a long time who studied the functions of the digestive glands (for these studies the scientist was awarded the Nobel Prize in 1904), discovered in experimental animals a regular increase in the secretion of saliva and gastric juice, not only when food enters the oral cavity and then into the stomach, but also just when waiting for the intake food. At that time, the mechanism of this phenomenon was unknown and was explained by “mental excitement salivary glands" As a result of further scientific research in this direction, scientists named this phenomenon as conditioned reflexes. According to I.P. Pavlov, conditioned reflexes are developed on the basis of unconditioned ones and are acquired in the process of life. In addition, conditioned reflexes are not constant, that is, they can appear and disappear throughout a person’s life, depending on changing living conditions. The acquisition of conditioned reflexes occurs throughout a person’s life. It is determined by the immediate, constantly changing environment. Newly acquired conditioned reflexes repeatedly increase and expand the range adaptive reactions animals and humans.

To develop a conditioned reflex, there must be a coincidence in time of two stimuli acting on an animal (or person). One of these stimuli, under any circumstances, causes a natural reflex reaction, classified as an unconditioned reflex. Such a stimulus itself is defined as a conditioned reflex. Another stimulus used to develop a conditioned reflex, due to its ordinariness, as a rule, does not cause any reaction and is defined as indifferent (indifferent). Stimuli of this kind, only at the first presentation, cause a certain response orienting reaction, which, for example, can manifest itself in turning the head and eyes towards the current stimulus. With repeated actions of the stimulus (irritant), the orienting reflex weakens and then completely disappears as a result of the habituation mechanism, and then the stimulus that caused it becomes indifferent.

As numerous studies by I.P. Pavlov and his colleagues have shown, a conditioned reflex is developed subject to the following rules:

1. The indifferent stimulus must act several seconds earlier than the unconditioned stimulus. I.P. Pavlov's research on dogs showed that if, for example, an indifferent stimulus (various sound signals) begins to act directly during the feeding process, and not before it begins, then a conditioned reflex is not formed.

2. The biological significance of the indifferent stimulus must be less than that of the unconditioned stimulus. Again, referring to the research conducted in the laboratory of I.P. Pavlov, it should be noted that if, for example, you use too loud, frightening sound signals, giving the animal food immediately after this, the conditioned reflex will not form.

3. The formation of a conditioned reflex should not be interfered with by extraneous stimuli that distract the animal’s attention.

We can speak of a developed conditioned reflex if a previously indifferent stimulus begins to evoke the same reaction as the unconditioned stimulus used in combination with it. Thus, if feeding an animal was preceded several times by the inclusion of a sound signal and, as a result of this combination, in the future only when sound signal salivation begins to occur, then this reaction should be considered a manifestation of a conditioned reflex. The action of an unconditioned stimulus following an indifferent one is defined as reinforcement, and when a previously indifferent stimulus begins to evoke a reflex response, it becomes a conditioned stimulus (conditioned signal).

There are several approaches to the classification of conditioned reflexes.

First of all, scientists divide all conditioned reflexes (as well as unconditioned ones) into the following groups.

According to biological significance they are distinguished into food, defensive, etc.

By receptor type , from which development begins, conditioned reflexes are divided into exteroceptive, proprioceptive, interoreceptive. In studies by V.M. Bykov and V.N. Chernigovsky and their colleagues, the connection between the cortex and cerebral hemispheres with everyone internal organs. Interoreceptive conditioned reflexes are usually accompanied by vague sensations, which I.M. Sechenov defined as “dark feelings” that affect mood and performance. Proprioceptive conditioned reflexes underlie the learning of motor skills (walking, industrial operations, etc.). Exteroceptive conditioned reflexes form adaptive behavior animals for obtaining food, avoiding harmful influences, procreation, etc. For a person, exteroceptive verbal stimuli that shape actions and thoughts are of utmost importance.

According to the function of the nervous system and the nature of the efferent response conditioned reflexes are distinguished between somatic (motor) and vegetative (cardiovascular, secretory, excretory, etc.).

In relation to the signal stimulus to the unconditioned (reinforcing) stimulus all conditioned reflexes are divided into natural and artificial (laboratory). Natural conditioned reflexes are formed to signals that are natural signs of a reinforcing stimulus (smell, color, certain time, etc.). For example, eating at the same time leads to the release of digestive juices and some other reactions of the body (for example, leukocytosis at the time of eating). Artificial (laboratory) are called conditioned reflexes to such signal stimuli that in nature are not related to the unconditioned (reinforced) stimulus. The main of these conditioned reflexes are the following:

· according to complexity they distinguish: simple conditioned reflexes produced to single stimuli (classical conditioned reflexes discovered by I.P. Pavlov); complex conditioned reflexes (reflexes formed under the influence of several signals acting either simultaneously or sequentially); chain reflexes - reflexes to a chain of stimuli, each of which causes its own conditioned reflex (a typical example here would be a dynamic stereotype),

· Based on the ratio of the time of action of the conditioned and unconditioned stimuli, a distinction is made between present and trace reflexes. The development of conditioned reflexes is characterized by the coincidence of the actions of conditioned and unconditioned stimuli. Trace reflexes are developed under conditions when the unconditioned stimulus is connected somewhat later in time (after 2-3 minutes) than the conditioned one. THOSE. the development of a conditioned reflex occurs in response to a signal stimulus,

· according to the development of a conditioned reflex on the basis of another conditioned reflex, conditioned reflexes of the first, second, third and other orders are distinguished. First-order reflexes are conditioned reflexes developed on the basis of unconditioned reflexes (classical conditioned reflexes). Second-order reflexes are developed on the basis of first-order conditioned reflexes, in which there is no unconditioned stimulus. A third-order reflex is formed on the basis of a second-order reflex, etc. The higher the order of the conditioned reflex, the more difficult it is to develop. Thus, in dogs it is possible to develop only conditioned reflexes of the third order (not higher),

· conditioned reflexes for a time can be not only natural, but also artificial. When an unconditioned stimulus is repeatedly presented with a constant interval between presentations, a timed reflex is formed. That is, some time before the supply of reinforcement, a conditioned effector reaction occurs.

Depending on the signaling system distinguish conditioned reflexes to signals of the first and second signaling systems, i.e. on external influences and on speech.

Besides, conditioned reflexes can be positive and negative .

Many scientists define conditioned reflexes as reactions to future events. Biological meaning conditioned reflexes lies in their preventive role. For the body, they have an adaptive significance, preparing the body for future useful behavioral activities and helping it avoid harmful effects, subtly and effectively adapt to the surrounding natural and social environment. It should also be noted that conditioned reflexes are formed due to the plasticity of the nervous system.

General characteristics of unconditioned and conditioned reflexes are presented in Table 1.

Table 1

General characteristics of unconditioned and conditioned reflexes

The path along which excitation spreads during the implementation of a reflex is called reflex arc ( Fig 2) .

The reflex arc consists of five main links:

1. Receptor.

2. Sensitive path.

3. Central nervous system.

4. Motor pathway.

5. Working body.

Fig.2. Reflex arc:

a – two-neuron; b – three-neurton

1 – receptor; 2 – sensitive (centripetal) nerve; 3 – sensory neuron in spinal glia; 4 – axon of a sensitive neuron; 5 – dorsal roots of spinal nerves; 6 – interneuron; 7 – axon of the intercalary nerve; 8 – motor neuron in the horns of the spinal cord; 9 – spinal cord; 10 – axon of a motor (centrifugal) neuron; 11 – working body.

A reflex arc is a chain of nerve cells, including afferent (sensitive) and effector (motor or secretory) neurons, along which a nerve impulse moves from its place of origin (from the receptor) to the working organ (effector). Most reflexes are carried out with the participation of reflex arcs, which are formed by neurons of the lower parts of the central nervous system - neurons of the spinal cord.

The simplest reflex arc consists of only two neurons - afferent (receptor) and effector (efferent). The body of the first neuron (afferent) is located outside the central nervous system. As a rule, this is a so-called unipolar neuron, the body of which is located in the spinal ganglion or in the sensory ganglion of the cranial nerves. The peripheral process of this cell is located in the spinal nerves or with sensory fibers of the cranial nerves and their branches and ends with a receptor that perceives external (from the external environment) or internal (in organs, tissues of the body) irritation. This irritation is transformed by the receptor into a nerve impulse, which reaches the body of the nerve cell, and then along the central process (the totality of such processes forms the posterior, sensitive roots of the spinal nerves) is sent to the spinal cord or along the corresponding cranial nerves to the brain. In the gray matter of the spinal cord or in the motor nucleus of the brain, this process of the sensitive cell forms a synapse with the body of the second neuron (efferent). In the interneuron synapse, with the help of mediators, nerve excitation is transferred from a sensitive (afferent) neuron to a motor (efferent) neuron, the process of which leaves the spinal cord as part of the anterior roots of the spinal nerves or motor (secretory) nerve fibers of the cranial nerves and is directed to the working organ, causing muscle contraction, or inhibition, or increased secretion of the gland.

Complex reflex arc. As a rule, the reflex arc does not consist of two neurons and is much more complex. Between two neurons - receptor (afferent) and effector (efferent) - there is one or more closure (intercalary) neurons. In this case, excitation from the receptor neuron along its central process is transmitted not directly to the effector nerve cell, but to one or more interneurons. The role of interneurons in the spinal cord is performed by cells located in the gray matter of the posterior columns. Some of these cells have an axon (neurite), which is directed to the motor cells of the anterior horns of the spinal cord at the same level and closes the reflex arc at the level of this segment of the spinal cord. The axon of other cells can pre-divide in a T-shape in the spinal cord into descending and ascending branches, which are directed to the motor cells of the anterior horns of the adjacent, superior and underlying segments. Along the route, each of the marked ascending or descending branches can send collaterals to the motor cells of these and other neighboring segments. In this regard, it should be noted that irritation of even the smallest number of receptors can be transmitted not only nerve cells of a specific segment of the spinal cord, but also spread to the cells of several neighboring segments. As a result, the response is a contraction of not one muscle or one muscle group, but several groups at once. Thus, in response to irritation, a complex reflex movement occurs - a reflex.

As we noted above, I.M. Sechenov in his work “Reflexes of the Brain” put forward the idea of ​​causality (determinism), noting that every phenomenon in the body has its own cause, and the reflex effect is a response to this cause. These ideas were continued and confirmed in the works of I.P. Pavlov and S.P. Botkin. It was I.P. Pavlov who extended the doctrine of reflex to the entire nervous system, from its lower parts to its higher parts, and experimentally proved the reflex nature of all forms of vital activity of the body without exception. According to I.P. Pavlov, simple form activity of the nervous system, which is constant, innate, specific and for the formation of structural prerequisites for which no special conditions are required, is an unconditioned reflex. Temporary connections acquired in the process of life activity, which allow the body to establish quite complex and diverse relationships with the environment, are, according to I.P. Pavlov’s definition, conditionally reflexive. The place of closure of conditioned reflexes is the cerebral cortex. Thus, the brain and its cortex are the basis of higher nervous activity.

Another scientist, P.K. Anokhin and his students confirmed the presence of the so-called feedback of the working organ with the nerve centers (this phenomenon is called “reverse afferentation”). At the moment when efferent impulses from the central nervous system reach the executive organs, they produce a response (movement or secretion). This operating effect irritates the receptors of the executive organ itself. The impulses that arise as a result of these processes are sent along afferent pathways back to the centers of the spinal cord or brain in the form of information about the execution of a certain action by the organ in each at the moment. Thus, it is possible to accurately record the correct execution of commands in the form of nerve impulses entering the working organs from the nerve centers, and their constant correction is carried out. The existence of two-way signaling along closed, circular or ring reflex nerve chains of “reverse afferentation” allows for constant, continuous, moment-to-moment corrections of any reactions of the body to any changes in conditions of the internal and external environment. Without feedback mechanisms, adaptation of living organisms to the environment would be impossible.

Thus, with scientific progress, the old ideas that the activity of the nervous system is based on an “open” (unclosed) reflex arc was replaced by the idea of ​​a closed, annular arc, which is a chain of reflexes.

The process of formation of a classical conditioned reflex goes through three main stages.

1. Pregeneralization stage. It is characterized by a pronounced concentration of excitation (mainly in the projection zones of the cortex of conditioned and unconditioned stimuli) and the absence of conditioned behavioral reactions.

2. The stage of generalization of the conditioned reflex, which is based on the process of “diffuse” spread (irradiation) of excitation. Conditioned reactions occur to signal and other stimuli (the phenomenon of afferent generalization), as well as in the intervals between presentations of the conditioned signal (inter-signal reactions). During this period, various bioelectrical shifts (blockade of the alpha rhythm, desynchronization, etc.) are widespread throughout the cortex and subcortical structures.

3. Specialization stage, when intersignal reactions fade and a conditioned response occurs only to the signal stimulus. Changes in biocurrents are more limited and are confined mainly to the action of a conditioned stimulus. This process ensures differentiation, subtle discrimination of stimuli, and specialization of the conditioned reflex skill. In the process of specialization, the sphere of distribution of biopotentials is significantly narrowed and the conditioned reflex response increases.

According to the results of research by I.P. Pavlov, a temporary connection is formed between the cortical center of the unconditioned reflex and the cortical center of the analyzer, the receptors of which are affected by the conditioned stimulus, i.e. the connection is made in the cerebral cortex). The basis of the closure of a temporary connection is dominance interaction process between excited centers. Impulses caused by an indifferent (conditioned) signal from any part of the skin and other sensory organs (eye, ear, etc.) enter the cerebral cortex and ensure the formation of a focus of excitation there. If, after an indifferent signal, food reinforcement (feeding) is given, then a more powerful second focus of excitation arises in the cerebral cortex, to which the previously arisen and irradiating excitation along the cortex is directed. Repeated combination of an indifferent (conditioned) signal and an unconditioned stimulus (reinforcement) facilitates the passage of impulses from the cortical center of the indifferent signal to the cortical representation of the unconditioned reflex.

I.P. Pavlov called the formation of a temporary connection in the cerebral cortex the closure of a new conditioned reflex arc.

Research by scientists has also proven that, in parallel with the formation of a conditioned reflex, the process is underway the formation of another conditioned reflex connection, specifically changing the state of neurons, which is expressed in an increase in their background activity. If for some reason a conditioned reflex change in the state of a given neuron does not occur, then the reflex developed by it is not detected. This enabled scientists to conclude that the associative response includes the formation of a state that is qualitatively specific for each temporary connection. This phenomenon is considered by physiologists as another of the leading mechanisms for the formation of conditioned reflex behavior.

Thus, according to I.P. Pavlov, there are two mechanisms of conditioned reflex activity:

1. tuning, regulating the state of the brain and creating a certain level of excitability and performance of nerve centers:

2. trigger, which initiates one or another conditioned reaction.

The modern explanation of the mechanism of formation of conditioned reflexes is based on the idea of ​​​​modifying the activity of synapses existing in those conditional points of the neural network that are capable of associating sensory signals that coincided in time.

Research by scientists has also proven that the process of formation of conditioned reflexes is directly related to memory. At the beginning of the development of a conditioned reflex, communication is carried out only with the help of short-term memory mechanisms - the spread of excitation occurs between two excited cortical centers. As the action of conditioned and unconditioned stimuli is repeated and the corresponding centers are repeatedly excited, short-term memory turns into long-term memory, that is, significant structural changes occur in neurons.

Conditioned reflexes, as shown by numerous studies, are changeable (variable), they can be inhibited.

We can distinguish two types of inhibition of conditioned reflexes, which are fundamentally different from each other: congenital and acquired (Fig. 3). Moreover, each type of braking has its own variations.

Unconditional Conditional(internal)

1. External 1. Extinctive

3. Differentiation

4.Conditional brake

Rice. 3. Inhibition of conditioned reflexes

Unconditioned (innate) inhibition conditioned reflexes are divided into external and transcendental. External braking manifests itself in the weakening or complete cessation of an existing (currently occurring) conditioned reflex under the influence of any extraneous stimulus. For example, turning on the light during the current conditioned reflex causes the appearance of an orienting-exploratory reaction, weakening or stopping the existing conditioned reflex activity. This reaction, which arose to a change in the external environment (reflex to novelty), I.P. Pavlov called the “what is it?” reflex. With the repetition of the additional stimulus, the reaction to this signal weakens and disappears, since the body does not need to take any action. I.P. Pavlov also studied the mechanism of this type of inhibition of conditioned reflexes. According to his theory, an extraneous signal is accompanied by the appearance in the cerebral cortex of a new focus of excitation, which, with an average strength of the stimulus, has a depressing effect on the current conditioned reflex activity according to the dominant mechanism. External inhibition is unconditional reflex. This type of inhibition was called external because in these cases the excitation of the cells of the orienting-exploratory reflex arising from an extraneous stimulus is outside the arc of the existing conditioned reflex. External inhibition contributes to the body’s emergency adaptation to changing conditions of the external and internal environment and provides the opportunity to switch to other activities in accordance with the situation.

Extreme braking occurs during prolonged nervous excitation of the body, under the influence of an extremely strong conditioned signal or several weak ones. There is a certain correspondence between the strength of the conditioned stimulus and the magnitude of the response - the “law of force”: the stronger the conditioned signal, the stronger the conditioned reflex reaction. However, this law can only be maintained up to a certain value (threshold), above which the effect begins to decrease, despite the continuing increase in the strength of the conditioned signal. These facts allowed I.P. Pavlov to conclude that cortical cells have a limit to their performance.

Conditioned (internal, acquired) inhibition conditioned reflexes are an active nervous process that requires development, like the reflex itself. It is no coincidence that this type of inhibition of a conditioned reflex is called conditioned reflex inhibition. It is acquired, individual. According to the theory of I.P. Pavlov, it is localized within (“within”) the nerve center of a given conditioned reflex. Distinguish the following types conditioned inhibition: extinctive, delayed, differentiated and conditioned inhibition.

Extinction inhibition occurs when a conditioned signal is repeatedly applied and its further non-reinforcement. In this case, at first the conditioned reflex weakens and then completely disappears. However, it may recover after some time. The rate of extinction depends on the intensity of the conditioned signal and the biological significance of the reinforcement. The more significant they are, the more difficult it is for the conditioned reflex to fade. It is precisely extinction inhibition that can explain the forgetting of previously received information, which long time does not repeat.

Delayed braking occurs when reinforcement lags by 1-3 minutes relative to the onset of the conditioned signal. Gradually, the appearance of the conditioned reaction shifts to the moment of reinforcement. This species Inhibition of the conditioned reflex is also characterized by the phenomenon of disinhibition.

Differential braking is produced with the additional inclusion of a stimulus close to the conditioned one, and without reinforcement of it.

Conditional brake occurs when another stimulus is added to the conditioned signal and this combination is not reinforced. So, if you develop a conditioned salivary reflex to light, then connect an additional stimulus (sound) to this signal, and do not reinforce this combination, then the conditioned reflex to it will gradually fade away.

The significance of all types of conditioned (internal) inhibition of conditioned reflexes is to eliminate unnecessary given time activity, that is, a very subtle adaptation of the body to the environment.

A fixed system of conditioned and unconditioned reflexes, combined into a single functional complex, is usually called dynamic stereotype. A dynamic stereotype is formed under the influence of stereotypically repeated changes and influences of the external and internal environment of the body. Stimuli that are repeated in the same sequence and act on the body are external stereotype. It corresponds to the stereotypical dynamics of cortical processes of excitation and inhibition, which, as a result of multiple repetitions of the external stereotype, begins to be reproduced in the same sequence as a single whole. After this, the stereotypical sequence of cortical processes can be caused not only by the action of an external stereotype (that is, a complex of stimuli), but also by the action of any one stimulus from this complex.

The concept of “dynamic stereotype” was introduced in the early 30s of the twentieth century, when I.P. Pavlov, proving his position regarding the reflex theory of the functioning of the nervous system. The opponents of the domestic scientist were mainly foreign researchers who argued that the reflex theory had ceased to contribute to the understanding of the functions of the brain and had become an obstacle to progress in this area of ​​knowledge. Defending and explaining his approach to the theory of reflexes, I.P. Pavlov identified “three basic principles of accurate scientific research” in reflex activity:

· the principle of determinism, that is, the reason, reason for any given action, effect;

· the principle of analysis and synthesis, that is, the primary decomposition of the whole into parts that make up units and then again the gradual addition of the whole from units, individual elements;

· the principle of structure, that is, the location of the actions of force in space. I.P. Pavlov comments on this principle as follows. When in the cortex and the nearest subcortex any stimulus causes excitation or inhibition of cells, then the excited and inhibited cells located in different parts of it form a dynamic combination with each other. Since the number of stimuli and options for their combination is innumerable, the dynamic combinations of excited and inhibited cells also cannot be taken into account. Such combinations can become stable and exist during the action of the stimulus. At the same time, they can remain as “imprints of reality” even after the termination of external influence. This means that the trace of previous influences can influence the nature of responses in the future, which, thus, will depend not only on the immediate stimulus, but also on previously learned experience.

I.P. Pavlov considered the formation and maintenance of a dynamic stereotype as “serious nervous work, varying depending on the complexity of the stereotype and the individuality of the animal.”

In the laboratory of I.P. Pavlov, various schemes for the development of dynamic stereotypes were used, some of which were relatively simple and consisted, for example, of only two positive reflexes. Others were complex combinations of positive, that is, exciting, and inhibitory stimuli. Rearranging the active stimuli of the complex, changing the meaning of individual stimuli from excitatory to inhibitory or vice versa made it possible to identify individual characteristics animal behavior. In the process of changing the dynamic stereotype, all animals became hyperexcited, stopped responding to the previous conditioned stimuli, sometimes refused food and resisted being introduced into the laboratory room. I.P. Pavlov called this state “painful” for the animal and explained it as “intense nervous labor,” which he considered not only as associative activity, but also as mental activity (labor).

Questions for self-control:

1. Define a reflex.

2. Expand the basic principles of the reflex principle of the central nervous system.

3. What types of reflexes exist?

4. What are the specific features of unconditioned reflexes.

5. Reveal the mechanism of formation of conditioned reflexes.

6. Classification of conditioned reflexes.

7. The mechanism of inhibition of conditioned reflexes.

8. What is the role of reflexes in the life of living organisms?

9. What is a reflex arc?

10. What is the structure of the reflex arc?

11. Describe the simplest reflex arc?

12. Reveal the mechanism of functioning of a complex reflex arc.

13. What is “reverse afferentation”?

14. What is the essence and significance of feedback mechanisms?

15. Expand the stages of formation of the classical conditioned reflex.

16. The mechanism of inhibition of conditioned reflexes.

17. What is the “law of force”?

18. What is the significance of inhibition of the conditioned reflex?

19. What is a dynamic stereotype?

The main form of activity of the nervous system is the implementation of reflexes. Reflexes- these are reactions of the body that occur in response to irritation of receptors and are carried out with the obligatory participation of the nervous system. Thanks to reflex reactions, the body constantly interacts with the environment, uniting and regulating the activities of all its organs and tissues.

The path along which the nerve impulse passes during the reflex is called reflex arc. The simplest reflex arcs have only two neurons, the more complex ones have three, and most reflex arcs have even more neurons. An example of a two-neuron reflex arc is the arc of the tendon knee reflex, which manifests itself in extension of the knee joint when lightly tapping the tendon below the kneecap (Fig. 66, A).

The three-neuron reflex arc (Fig. 66, B) includes: 1) receptor; 2) afferent neuron; 3) interneuron; 4) efferent neuron; 5) working organ (muscle or gland cells). Communication between neurons in the reflex arc, between the efferent neuron and the cells of the working organ is carried out using synapses.

Receptors call the endings of the dendrites of afferent neurons, as well as specialized formations (for example, rods and cones of the retina), which perceive irritation and generate nerve impulses in response to it. Nerve impulses from the receptor travel along the afferent nerve pathway, consisting of the dendrite, body and axon of the afferent neuron, to the nerve center.

Nerve center called a set of neurons necessary for the implementation of a reflex or regulation of a particular function. Most nerve centers are located in the central nervous system, but they are also found in the nerve ganglia of the peripheral nervous system. Neurons whose bodies lie in different parts of the nervous system can be functionally combined into one nerve center.

In the nerve center there is an interneuron, to the body or dendrites of which excitation from the axon of the afferent neuron is transmitted. The impulse travels along the axon of the interneuron to the efferent neuron, the body of which is also located in the nerve center. In most reflex arcs between the axon of the afferent neuron and the body of the efferent neuron, not one, but a whole chain of interneurons is included. These reflex arcs are called polyneuron, or polysynaptic.

Along the axon of the efferent neuron, nerve impulses travel to the cells of the working organ (muscles, glands). As a result, a reflex reaction (movement, secretion) to receptor irritation is observed. The time from the beginning of receptor stimulation to the beginning of the response is called reaction time, or reflex latency time. Most of all, the reflex time depends on the speed of excitation through the nerve centers. Deterioration of the functional state of the nerve center leads to an increase in reflex time.

Execution of a response is not yet the end of the reflex act. In the working organ that carries out the response, receptors are irritated, impulses from which arrive along afferent nerve fibers to the central nervous system and inform the nerve centers about the course of the reflex reaction and the state of the working organ. This information is called feedback. There are positive and negative feedbacks. Positive feedback causes the continuation and strengthening of the reflex response, and negative feedback causes its weakening and cessation.

Thus, excitation during a reflex reaction is not only transmitted along the reflex arc from the initially stimulated receptor to the working organ, but also then again enters the central nervous system from the receptors of the working organ, which were excited as a result of its reflex response. This relationship between nerve centers and innervated organs, which is observed during the implementation of a reflex, is called reflex ring. Thanks to feedback connections carried out along the reflex ring, the central nervous system receives information about the results of reflex reactions, makes amendments to their implementation, and ensures the coordinated activity of the body.

All activity of the nervous system is of a reflex nature, i.e. consists of a huge number of different reflexes different levels complexity. Reflex- this is the body’s response to any external or internal influence involving the nervous system. The authors of the reflex theory are I.P. Pavlov and I.M. Sechenov.

Each reflex has:

• reflex time - the time from the application of irritation to the response to it
• receptive field - a certain reflex occurs only when a certain receptor zone is irritated
• nerve center - a specific localization of each reflex in the central nervous system.

Unconditioned reflexes are specific, constant, hereditary, and persist throughout life. During the process of embryonic development, reflex arcs of all unconditioned reflexes are formed. A set of complex innate reflexes is instincts. Conditioned reflexes are individual, acquired during a person’s life, and are not inherited. The person has a complex social behavior, thinking, consciousness, individual experience (higher nervous activity) is a combination of a huge number of diverse conditioned reflexes. The material basis of conditioned reflexes is the cerebral cortex. The coordination of all reflex reactions is carried out in the central nervous system due to the processes of excitation and inhibition of neuronal activity.

To implement any reflex, a special anatomical formation is necessary - reflex arc. Reflex arc - this is a chain of neurons through which a nerve impulse passes from the receptor (perceiving part) to the organ that responds to irritation.

The simplest reflex arc in humans is formed by two neurons - sensory and motor (motoneuron). An example of a simple reflex is the knee reflex. In other cases, three (or more) neurons are included in the reflex arc - sensory, intercalary and motor. In a simplified form, this is a reflex that occurs when a finger is pricked with a pin. This is a spinal reflex; its arc passes not through the brain, but through the spinal cord. The processes of sensory neurons enter the spinal cord as part of the dorsal root, and the processes of motor neurons exit the spinal cord as part of the anterior root. The bodies of sensory neurons are located in the spinal ganglion of the dorsal root (in the dorsal ganglion), and intercalary and motor neurons are located in the gray matter of the spinal cord.

Question No. 3

Carbohydrate metabolism

Carbohydrates enter the human body as part of food in the form monosaccharides (glucose, fructose, galactose), disaccharides(sucrose, maltose, lactose) and polysaccharides(starch, glycogen). Up to 60% of human energy metabolism depends on the transformation of carbohydrates. The oxidation of carbohydrates occurs much faster and easier compared to the oxidation of fats and proteins. In the human body, carbohydrates perform a number of functions important functions:

• energy ( with the complete oxidation of one gram of glucose, 17.6 kJ of energy is released) ;
• receptor(form carbohydrate receptors
• protective(part of mucus);
• storing ( stored in the muscles and liver in the form of glycogen);

In the human digestive tract, polysaccharides and disaccharides are broken down into glucose and other monosaccharides. In the body, excess carbohydrates from the blood under the influence of the hormone insulin are stored in the form of polysaccharides. glycogen in the liver and muscles. With a lack of insulin, a serious illness develops - diabetes mellitus

Daily requirement person in carbohydrates 400 - 600 grams. Plant foods are rich in carbohydrates. If there is a lack of carbohydrates in food, they can be synthesized from fats and proteins. Excess carbohydrates in food are converted into fats during metabolism.

Water and salt metabolism

The human body contains about 65% water. Nervous tissue cells (neurons), spleen and liver cells contain especially large amounts of water – up to 85%. Daily water loss is 2.5 liters. Replenishment of water loss is carried out through food and fluid consumption. About 300g of water is formed inside the body every day due to the oxidation of proteins, fats and carbohydrates. Water like chemical substance has a number of unique physical and chemical properties, on what are the functions it performs in the body based: