Textbook for 8th grade

Higher nervous activity

Higher nervous activity (HNA) refers to all those nervous processes that underlie human behavior, ensuring each person’s adaptation to rapidly changing and often very complex and unfavorable living conditions. The material basis of higher nervous activity is the brain. It is into the brain that all the information about what is happening in the world around us flows. Based on a very fast and accurate analysis of this information, the brain makes decisions that lead to changes in the activity of body systems, ensuring optimal (best under these conditions) interaction between a person and the environment, maintaining the constancy of his internal environment.

Reflex activity of the nervous system

The idea that mental activity is carried out with the participation of the nervous system arose in ancient times, but how this happens remained unclear for a very long time. Even now it cannot be said that the mechanisms of the brain are fully revealed.

The first scientist to prove the participation of the nervous system in the formation of human behavior was the Roman physician Galen (2nd century AD). He discovered that the brain and spinal cord are connected to all other organs by nerves and that rupture of the nerve connecting the brain and muscle leads to paralysis. Galen also proved that when the nerves coming from the sensory organs are cut, the body ceases to perceive stimuli.

The origin of brain physiology as a science is associated with the works of the French mathematician and philosopher Rene Descartes (17th century). It was he who laid down the ideas about the reflex principle of the body’s functioning. True, the term “reflex” itself was proposed in the 18th century. Czech scientist I. Prochazka. Descartes believed that the basis of the activity of the brain, as well as the entire human body, are the same principles as the basis of the operation of the simplest mechanisms: watches, mills, blacksmith's bellows, etc. Explaining simple human movements from a completely materialistic position, R. Descartes recognized the presence of a soul, which controls the complex and diverse behavior of man.

What is a reflex? A reflex is the most correct, most common reaction of the body to external stimuli, which is carried out through the nervous system. For example, a child touched a hot stove with his hand and immediately felt pain. The only correct decision that the brain always makes in this situation is to pull your hand away so as not to get burned.

At a higher level, the doctrine of the reflex principle of the body’s activity was developed by the great Russian physiologist Ivan Mikhailovich Sechenov (1829-1905). The main work of his life - the book “Reflexes of the Brain” - was published in 1863. In it, the scientist proved that a reflex is a universal form of interaction of the organism with the environment, i.e. not only involuntary, but also voluntary - conscious ones have a reflex character movements. They begin with irritation of any sensory organs and continue in the brain in the form of certain nervous phenomena that lead to the launch of behavioral programs. I.M. Sechenov was the first to describe inhibitory processes developing in the central nervous system. In a frog with destroyed cerebral hemispheres of the brain, the scientist studied the reaction to irritation of the hind leg with an acid solution: in response to a painful stimulus, the leg bent. Sechenov discovered that if in an experiment a salt crystal is first applied to the surface of the midbrain, the time until the response will increase. Based on this, he concluded that reflexes could be inhibited by some strong influences. A very important conclusion made by scientists at the end of the 19th - beginning of the 20th century was the conclusion that any response of the body to a stimulus is always expressed by movement. Any sensation, consciously or unconsciously, is accompanied by a motor response. By the way, it is precisely on the fact that any reflex ends with the contraction or relaxation of muscles (i.e., movement), that the work of lie detectors is based, capturing the smallest, unconscious movements of an excited, alarmed person.

The assumptions and conclusions of I.M. Sechenov were revolutionary for their time, and not all scientists at that time immediately understood and accepted them. Experimental evidence of the truth of I. M. Sechenov’s ideas was obtained by the great Russian physiologist Ivan Petrovich Pavlov (1849 1936). It was he who introduced scientific language the term "higher nervous activity". He believed that higher nervous activity is equivalent to the concept of “mental activity.”

Indeed, both sciences - physiology of GNI and psychology study the activity of the brain; They are also united by a number of common research methods. At the same time, the physiology of GNI and psychology study different aspects of the work of the brain: physiology of GNI - the mechanisms of activity of the entire brain, its individual structures and neurons, connections between structures and their influence on each other, as well as mechanisms of behavior; psychology - the results of the work of the central nervous system, manifested in the form of images, ideas, concepts and other mental manifestations. Scientific research by psychologists and physiologists of GNI has always been interdependent. In recent decades, a new science has even emerged - psychophysiology, the main task of which is to study the physiological foundations of mental activity.

I. P. Pavlov divided all reflexes that arise in the body of an animal or a person into unconditioned and conditioned.

Unconditioned reflexes. Unconditioned reflexes ensure the body's adaptation to constant environmental conditions. In other words, this is the body’s reaction to strictly defined external stimuli. All animals of the same species have a similar set of unconditioned reflexes. Therefore, unconditioned reflexes are classified as species characteristics.

An example of unconditioned reflexes is the occurrence of a cough when foreign bodies enter the respiratory tract, or the withdrawal of a hand when pricked by rose thorns.

Already in a newborn child, unconditioned reflexes are observed. This is understandable, because it is impossible to live without them, and there is no time to learn: breathing, eating, avoiding dangerous influences is necessary from the very first moments of life. One of the important reflexes of newborns is the sucking reflex - an unconditioned food reflex. An example of a protective unconditioned reflex is the constriction of the pupil in bright light.

The role of unconditioned reflexes is especially important in the life of those creatures whose existence lasts only a few days, or even just one day. For example, the female of one species of large solitary wasp emerges from the pupa in the spring and lives only for a few weeks. During this time, she must have time to meet the male, catch prey (spider), dig a hole, drag the spider into the hole, and lay eggs. She performs all these actions several times throughout her life. The wasp emerges from the pupa as an “adult” and is immediately ready to carry out its activities. This does not mean that she is not capable of learning. For example, she can and should remember the location of her burrow.

More complex forms of behavior - instincts - are a chain of sequentially interconnected reflex reactions that follow one after another. Here, each individual reaction serves as a signal for the next one. The presence of such a chain of reflexes allows organisms to adapt to a particular situation or environment.

A striking example of instinctive activity is the behavior of ants, bees, birds when building a nest, etc.

In highly organized vertebrates the situation is different. For example, a wolf cub is born blind and completely helpless. Of course, at birth he has a number of unconditioned reflexes, but they are not enough for a full life. In order to adapt to existence in constantly changing conditions, it is necessary to develop a wide range of conditioned reflexes. Conditioned reflexes, developed as a superstructure over innate reflexes, greatly increase the body’s chances of survival.

Conditioned reflexes. Conditioned reflexes are reactions acquired during the life of each person or animal, with the help of which the body adapts to changing environmental influences. For the formation of a conditioned reflex, the presence of two stimuli is necessary: ​​conditioned (indifferent, signal, indifferent to the reaction being developed) and unconditioned, causing a certain unconditioned reflex. The conditioned signal (flash of light, sound of a bell, etc.) should be somewhat ahead of the unconditional reinforcement in time. Typically, a conditioned reflex is developed after several combinations of conditioned and unconditioned stimuli, but in some cases, one presentation of conditioned and unconditioned stimuli is enough to form a conditioned reflex.

For example, if you turn on the light bulb several times before giving the dog food, then, starting at some point, the dog will approach the feeder and salivate every time the light is turned on, even before the food is presented to it. Here light becomes a conditioned stimulus, signaling that the body should prepare for an unconditioned reflex food reaction. A temporary functional connection is formed between the stimulus (light bulb) and the food reaction. A conditioned reflex is developed during the learning process, and the connection between the sensory (in our case, visual) system and the effector organs that ensure the implementation of the food reflex is formed based on the combination of a conditioned stimulus and unconditional reinforcement of it with food. So, for the successful development of a conditioned reflex, three conditions must be met. First, the conditioned stimulus (in our example, light) must precede the unconditional reinforcement (in our example, food). Secondly, the biological significance of the conditioned stimulus must be less than that of the unconditioned reinforcer. For example, for a female of any mammal, the cry of her cub is obviously a stronger irritant than food reinforcement. Thirdly, the strength of both conditioned and unconditioned stimuli must have a certain magnitude (the law of strength), since very weak and very strong stimuli do not lead to the development of a stable conditioned reflex.

A conditioned stimulus can be any event that occurred in the life of a person or animal that coincided several times with the action of reinforcement.

The brain, capable of developing conditioned reflexes, considers conditioned stimuli as signals indicating the imminent appearance of reinforcement. Thus, an animal that has only unconditioned reflexes can only eat food that it accidentally stumbles upon. An animal capable of developing conditioned reflexes associates a previously indifferent smell or sound with the presence of food nearby. And these stimuli become a hint that forces him to more actively search for prey. For example, pigeons can sit calmly on the eaves and window sills of some architectural landmark, but as soon as a bus with tourists approaches them, the birds will immediately begin to descend to the ground, expecting to be fed. Thus, the sight of a bus, and especially tourists, is a conditioned stimulus for pigeons, indicating that they need to take a more comfortable place and start fighting with rivals for food.

As a result, an animal capable of quickly developing conditioned reflexes will be more successful in obtaining food than one that lives using only a set of innate unconditioned reflexes.

Braking. If unconditioned reflexes are practically not inhibited throughout life, then developed conditioned reflexes can lose their significance when the conditions of the organism’s existence change. The extinction of conditioned reflexes is called inhibition.

There are external and internal inhibition of conditioned reflexes. If, under the influence of a new strong external stimulus, a focus of strong excitation appears in the brain, then the previously developed conditioned reflex connection does not work. For example, a dog’s conditioned food reflex is inhibited by strong noise, fear, exposure to a painful stimulus, etc. This type of inhibition is called external. If the salivation reflex developed in response to a bell is not reinforced by feeding, then gradually the sound ceases to act as a conditioned stimulus; the reflex will begin to fade and will soon slow down. The temporary connection between the two excitation centers in the cortex will be destroyed. This type of inhibition of conditioned reflexes is called internal.

Skills. A separate category of conditioned reflexes includes motor conditioned reflexes developed throughout life, i.e. skills, or automated actions. A person learns to walk, swim, ride a bike, and type on a computer keyboard. Learning takes time and persistence. However, gradually, when the skills are already established, they are performed automatically, without conscious control.

During his life, a person masters many special motor skills related to his profession (working a machine, driving a car, playing a musical instrument).

Possession of skills is beneficial for a person because it saves time and energy. Consciousness and thinking are freed from control over operations that have become automated and become skills in everyday life.

Works by A. A. Ukhtomsky and P. K. Anokhin

At every moment of life, a person is affected by many external and internal stimuli - some of them are very important, while others can be neglected at the moment. After all, the body cannot ensure the simultaneous implementation of many reflexes. You should not even try to satisfy the need for food while you are running away from the dog. You have to choose one thing. According to the great Russian physiologist Prince A. A. Ukhtomsky, a single focus of excitation temporarily dominates in the brain, as a result of which the execution of one reflex that is vital at the moment is ensured. A. A. Ukhtomsky called this focus of excitation a dominant (from the Latin “dominance” - dominant). Dominants constantly replace each other as the main needs at some point are satisfied and new ones arise. If the need for food after a heavy lunch has passed, the need for sleep may arise, and a completely different dominant will arise in the brain, aimed at searching for a sofa and pillow. The dominant focus inhibits the work of neighboring nerve centers and, as it were, subordinates them to itself: when you want to eat, the sense of smell and taste are heightened, and when you want to sleep, the sensitivity of the senses weakens. The dominant underlies such mental processes as attention, will, and makes human behavior active and selectively aimed at satisfying the most important needs.

Since the body of an animal or a person cannot fully respond to several different stimuli at the same time, it is necessary to establish something like a “queue”. Academician P.K. Anokhin believed that in order to satisfy the most important need at the moment, various systems and organs are combined into a so-called “functional system”, consisting of many sensitive and working links. This functional system “works” until the desired result is achieved. For example, when a person feels hungry, he feels full. Now the same systems that participated in the search, production, and absorption of food can unite into another functional system and participate in satisfying other needs.

Sometimes previously developed conditioned reflexes persist for a long time, even if they no longer receive unconditional reinforcement.

• In the English cavalry of the mid-19th century. horses have been trained for years to charge in close formation. Even if the rider was knocked out of the saddle, his horse had to gallop in a general formation side by side with other horses and make a U-turn with them. During the Crimean War, in one of the attacks, the cavalry unit suffered very heavy losses. But the surviving part of the horses, turning around and maintaining formation as much as possible, returned to the starting position, saving those few wounded cavalrymen who were able to stay in the saddles. As a token of gratitude, these horses were sent from Crimea to England and kept there in excellent conditions, without being forced to walk under saddle. But every morning, as soon as the stable doors opened, the horses ran out onto the field and lined up. Then the leader of the herd gave a signal by neighing, and the line of horses rushed in perfect order across the entire field. At the edge of the field, the line turned around and returned to the stable in the same order. And this was repeated day after day... This is an example of a conditioned reflex that persisted for a long time without unconditional reinforcement.

Test your knowledge

1. What are the merits of I.M. Sechenov and I. P. Pavlov in the development of the doctrine of higher nervous activity?
2. What is an unconditioned reflex?
3. What unconditioned reflexes do you know?
4. What underlies the innate form of behavior?
5. How does a conditioned reflex differ from an unconditioned reflex?
6. What is instinct?
7. What conditions are necessary for the development of a conditioned reflex?
8. What forms of behavior can be classified as acquired?
9. Why can a conditioned reflex fade over time?
10. What's the point conditioned inhibition?

Think

As a result, the conditioned reflex fades away? What is the biological meaning of this phenomenon?

The basis of nervous activity is a reflex. There are innate and acquired behavior. They are based on unconditioned and conditioned reflexes. Complex shape acquired behavior is rational activity, this is the beginning of thinking. Conditioned reflexes may fade. There are unconditioned and conditioned inhibition.

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

REFLEX REGULATION OF THE ACTIVITY OF ORGANS, SYSTEMS AND ORGANISM

Regulation based on the reflex principle was deeply studied and formalized into the doctrine of nervism by I. M. Sechenov and I. P. Pavlov. According to their concept, the nervous system operates on the principle of a reflex. The activity of the nervous system on the principle of a reflex is called reflex.

Reflex is a natural response of the body to irritation of receptors, carried out with the participation of the central nervous system.

The reflex is carried out through a special structural formation of the nervous system, which is called reflex arc. Three types of neurons are involved in the formation of a reflex arc: sensory, contact and motor.

They are combined into neural circuits. Neurons contact each other and the executive organ using synapses. Receptor neurons are located outside the central nervous system, contact and motor neurons are located in the central nervous system. A reflex arc can be formed by a different number of neurons of all three types. In turn, there are 5 links in the reflex arc: receptor, afferent pathway, nerve center, efferent pathway and working organ, or effector.

A receptor is a formation that perceives irritation. It is either a branching end of the dendrite of a receptor neuron, or specialized, highly sensitive cells, or cells with auxiliary structures that form the receptor organ.

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

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

This is a complex formation of a reflex arc, which is an ensemble of neurons located in various parts of the central nervous system, including the cerebral cortex and providing a specific adaptive reaction.

The nerve center has four physiological roles: perception of impulses from receptors through the afferent pathway; analysis and synthesis of perceived information; transmission of the generated program along a centrifugal path; perception of feedback from the executive body about the implementation of the program, about the completed action.

The efferent link is formed by the axon of a motor neuron and conducts excitation from the nerve center to the working organ.

A working organ is one or another organ of the body that carries out its characteristic activity.

The principle of the reflex. Through reflex arcs, adaptive responses to the action of stimuli, i.e., reflexes, are carried out.

Receptors perceive the action of stimuli, a stream of impulses arises, which is transmitted to the afferent link and through it enters the neurons of the nerve center. The nerve center perceives information from the afferent link, carries out its analysis and synthesis, determines its biological significance, forms an action program and transmits it in the form of a stream of efferent impulses to the efferent link. The efferent link ensures the implementation of the action program from the nerve center to the working organ. The working body carries out its characteristic activities. The time from the onset of the stimulus to the onset of the organ response is called reflex time.

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

Classification of reflexes. The reflexes of animals and humans are diverse, so they are classified according to a number of principles: by nature into unconditional and conditional.

Unconditioned reflexes are innate and hereditary. Unconditioned reflexes are carried out through formed reflex arcs. Unconditioned reflexes are specific, that is, they are characteristic of all animals of a given species. They are relatively constant and occur in response to adequate stimulation of certain receptors. Unconditioned reflexes are classified according to biological significance for nutritional, defensive, sexual, statokinetic and locomotor, orientation, maintaining homeostasis, etc.; by receptor location: exteroceptive; interoceptive; proprioceptive; by the nature of the response: motor, secretory, etc.; at the location of the centers through which reflexes are carried out: spinal, bulbar, mesencephalic, diencephalic, cortical.

Conditioned reflexes are reflexes acquired by an organism during its individual life. Conditioned reflexes are carried out through newly formed reflex arcs on the basis of reflex arcs of unconditioned reflexes with a temporary connection in the cerebral cortex between certain sensory zones and the cortical representation of the nerve center of the reflex arc of the unconditioned reflex.

Each reflex has its own name, depending on the response it provides.

Reflexes in the body are often carried out with the participation of endocrine glands and hormones. Joint reflex-hormonal regulation is the main form of regulation in the body.

Properties of nerve centers. The features of reflex activity are largely determined by the properties of the nerve centers:

unilateral conduction of excitation: from afferent neuron to effector neuron;

excitation is carried out slowly;

the action of one stream of impulses facilitates the action of the subsequent one; property relief, or summation;

is happening transformation of the rhythm of impulses, the strength of the impulses also changes;

characteristic occlusion; with the simultaneous arrival of two afferent flows, the number of excited neurons is less than arithmetic sum excitations for each stream of impulses separately;

manifests itself aftereffect", excitation persists for some time after the influx of impulses stops. The aftereffect is determined by the circular connections of neurons;

characteristic fatigue, decreased activity during prolonged activity due to a decrease in transmitter reserves in synapses;

are in a state constant tone, some excitement;

under certain conditions, after a long previous arrival of pulses of a frequent rhythm, the nerve center remains in a state of increased excitability for a certain time - post-tetanic potency;

characteristic braking, weakening or cessation of activity.

Coordination of reflex activity. Reflex activity is associated with coordination - the interaction of neurons, and consequently, nervous processes in the central nervous system, ensuring the coordinated activity of nerve centers. Coordination is carried out on the basis of certain principles, phenomena and phenomena.

The principle of convergence. Impulses from many afferent pathways converge to the nerve center; there are 4-5 times more of them than efferent ones.

The phenomenon of irradiation. Excitation arising in the center radiates - spreads to neighboring areas of the central nervous system.

The principle of reciprocal innervation. Such a relationship between nerve centers when the excitation of one inhibits the activity of the other.

The phenomenon of induction -- guidance from one nerve center to another of the opposite nervous process. If inhibition induces excitation, then the induction is positive; if excitation induces inhibition, then the induction is negative.

The phenomenon of "recoil"-- consists in a rapid change of excitation of one center by excitation of another, providing reflexes of opposite significance.

The phenomenon of chain and rhythmic excitations nerve centers. The excitation of one nerve center causes the excitation of another, etc. Thus, food intake is associated with the capture of food, chewing, and swallowing.

The alternation in a certain sequence of the same simple reflex acts is called rhythmic stimulation of nerve centers.

Feedback principle. In the body, as a result of the activity of organs, certain impulses are born, which enter the center and inform about the parameters of the action performed.

The principle of a common final path. The same response can be evoked from different receptor fields through one center. The effector neuron of the center forms a common final path.

The principle of dominance. At each period of time, one or another center dominates in the central nervous system. To a certain extent, it subordinates the activities of other centers.

Plasticity of nerve centers; manifests itself in the adaptability and variability of its functional significance when the nature of connections with receptors and effectors changes.

Nerve centers have a characteristic role trophic regulator, which manifests itself in the adaptation of metabolic processes in organ tissues to changing conditions in order to maintain them structural organization and activities.

• Central nervous system (CNS)- the brain and spinal cord
• Peripheral nervous system- these are nerves extending from the central nervous system (12 pairs of cranial and 31 pairs of spinal), nerve ganglia and nerve plexuses outside the central nervous system. The peripheral nervous system provides communication between the brain and spinal cord and all organs of the body.

• Somatic nervous system(innervates skeletal muscles, ensuring their contractions, forms receptors for the skin and sensory organs)
• Autonomic (autonomic) nervous system(innervates all internal organs, including skeletal muscles, sensory organs and skin, regulating metabolic processes in them); divided into sympathetic and parasympathetic nervous system. The sympathetic nervous system as a whole accelerates the intensity of metabolic processes, increases the speed of physiological reactions, and is active during various physical and mental activities, and in a state of stress. The parasympathetic nervous system performs an inhibitory function, slowing down the intensity of metabolic processes, reducing the speed of physiological reactions. Majority internal organs innervated by the sympathetic and parasympathetic nervous system, due to which the activity of the organs is precisely adjusted to the needs 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 difficulties. Reflex- this is the body’s response to any external or internal influence involving the nervous system. Reflex is an adaptive reaction of the body that ensures a subtle, precise and perfect balance of the body with the state of the external or internal environment. “If you turn off all the receptors, then a person should fall asleep and never wake up” (I.M. Sechenov). That. The nervous system works on the principle of reflection: stimulus - response. The authors of the reflex theory are outstanding Russian physiologists I.P. Pavlov and I.M. Sechenov.

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

The reflex arc consists of 5 links:

1. receptor, perceiving external or internal influences; receptors convert the influencing energy into the energy of a nerve impulse; receptors have very high sensitivity and specificity (certain receptors perceive only a certain type of energy)
2. sensitive (centripetal, afferent) a neuron formed by a sensory neuron through which the nerve impulse enters the central nervous system
3. interneuron, lying in the central nervous system, along which the nerve impulse switches to the motor neuron
4. motor neuron (centrifugal, efferent), along which the nerve impulse is conducted to the working organ that responds to irritation
5. nerve endings - effectors, transmitting a nerve impulse to a working organ (muscle, gland, etc.)

The reflex arcs of some reflexes do not have interneurons, for example the knee reflex.

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.

Classification of reflexes

1. According to biological significance:

• food
• defensive
• indicative
• sexual
• and etc.

• motor
• secretory
• vascular
• and etc.

• spinal(nerve centers are located in the spinal cord - urination, defecation, etc.)
• bulbar(nerve centers are located in the medulla oblongata - coughing, sneezing, etc.)
• mesencial(nerve centers are located in the midbrain - straightening the body, walking)
• diencephalic(in the diencephalon - thermoregulation, etc.)
• cortical(nerve centers are located in the cerebral cortex - all conditioned reflexes).

• simple
• complex(chain reflexes)

• vegetative
• somatic

• congenital (unconditional)
• acquired (conditional).

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. A person has complex social behavior, thinking, consciousness, individual experience (higher nervous activity) - this is a combination of a huge number of diverse conditioned reflexes. The material basis of conditioned reflexes is the cerebral cortex. The author of the doctrine of higher nervous activity is the outstanding Russian physiologist I.P. Pavlov, laureate Nobel Prize(1904).

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.

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 phase. 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 organism and 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 C. 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:

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, an influence from outside 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).

The principle of structure. Its essence lies in the fact that the reflex reaction is carried out using certain structures. The more structures structural elements participates in the implementation of 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.

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 useful information from the environment, 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 of 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 of unconditioned reflexes:

vital unconditioned reflexes that ensure individual and species preservation of the body (food, drinking, 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 toward 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 the “what is this?” reflex. 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 an emergency situation, 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, who studied the functions of the digestive glands for a long time (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 ingested food into the oral cavity, and then into the stomach, but also with just the anticipation of eating. At that time, the mechanism of this phenomenon was unknown and was explained by “mental stimulation of the salivary glands.” As a result of further scientific research in this direction, this phenomenon was called by scientists 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 greatly increase and expand the range of adaptive reactions of 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 (stimulant), 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:

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.

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.

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, salivation began to occur only when there was a sound signal, 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 reaction, 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. The studies of V.M. Bykov and V.N. Chernigovsky and their colleagues showed the connection of the cerebral cortex with all 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 the adaptive behavior of animals in 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,

Based on 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 to avoid harmful effects, to 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:

Receptor.

Sensitive way.

Central nervous system.

Motor path.

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 gray matter 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 closing (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 stimulation of even the smallest number of receptors can be transmitted not only to the nerve cells of a particular 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, a simple form of 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 performance of a certain action by the organ at any given 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.

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.

The stage of generalization of a 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 bioelectric shifts (blockade of the alpha rhythm, desynchronization, etc.) are widespread throughout the cortex and subcortical structures.

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, there is a process of formation of another conditioned reflex connection, which specifically changes 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:

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

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 that exist 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 promotes emergency adaptation of the body 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. The following types of conditioned inhibition are distinguished: 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 is not repeated for a long time.

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 the elimination of activities that are unnecessary at a given time, 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 cessation 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 current stimuli of the complex, changing the meaning of individual stimuli from excitatory to inhibitory or vice versa made it possible to identify individual characteristics of the animals' 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 condition “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:

Define reflex.

Reveal the basic principles of the reflex principle of the central nervous system.

What types of reflexes are there?

What are the specific features of unconditioned reflexes.

Reveal the mechanism of formation of conditioned reflexes.

Classification of conditioned reflexes.

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

What is a reflex arc?

What is the structure of the reflex arc?

Describe the simplest reflex arc?

Reveal the mechanism of functioning of a complex reflex arc.

What is “reverse afferentation”?

What is the essence and significance of feedback mechanisms?

Expand the stages of formation of the classical conditioned reflex.

The mechanism of inhibition of conditioned reflexes.

What is the “law of force”?

What is the significance of inhibition of a conditioned reflex?

What is a dynamic stereotype?

All activity of the nervous system is of a reflex nature, i.e. consists of a huge number of different reflexes of different levels of 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. A person has complex social behavior, thinking, consciousness, individual experience (higher nervous activity) - this 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 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.

The daily human need for carbohydrates is 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 physicochemical properties, on which the functions it performs in the body are based: