Section tasks: characterize the processes of irradiation and concentration of excitation and inhibition, consider the law of mutual induction and its manifestation, study the phenomenon of the dominant and its role in mental processes, get acquainted with physiological foundations and theories of sleep and dreams, sleep hygiene.

Lesson 1. IRRADIATION AND CONCENTRATION OF NERVE PROCESSES

Equipment: tables, diagrams and figures illustrating the processes of irradiation and concentration of excitation and inhibition.

DURING THE CLASSES

I. Learning new material

Dynamics of nervous processes in a network of neurons

All the complex and varied activities of the higher departments nervous system It is built on the work of two main nervous processes - excitation and inhibition. Flowing in mobile spatial and temporal relations with each other, these processes either spread (radiate), then concentrate (concentrate) in certain points of the cortex, then excitation gives rise to inhibition (negative induction), then inhibition gives rise to excitation (positive induction).

The continuous interaction of excitatory and inhibitory processes that move and call each other creates an extremely fine mosaic in the higher parts of the brain, an oscillating pattern of interweaving of excited and inhibited neurons. Such mosaics underlie both various acts of behavior and their inhibition in sleep phenomena.

Irradiation inhibition

Excitation or inhibition that has arisen in any cell or group of brain cells is always prone to spread. The spread of a nervous process from its site of origin to the surrounding nerve cells is called irradiation(from lat. irradiare- shine).

It is convenient to observe the irradiation of conditioned inhibition in a skin analyzer. A considerable area of ​​this analyzer is like a magnifying mirror, in which one can clearly see how an inhibitory state, for example, differential inhibition, will radiate through sequentially arranged projection fields.

Rice. 1. Experiment with irradiation of differential inhibition through the cortical cells of the skin analyzer:
0 - differentiation stimulus; 1, 2, 3, 4 - positive conditioned stimuli (applied to points on the skin of the leg at a distance from the differentiating stimulus, respectively, by 3, 9, 15 and 22 cm)

Irradiation of differential inhibition was found in the following experiment (Fig. 1). Along the hind leg of the dog, from the foot to the thigh, five "casals" were glued - devices for mechanical skin irritation. The four upper winders were used to develop conditioned alimentary salivary reflexes and the same salivary effects were obtained from these stimuli. The lower cassette served as a differentiation stimulus and was used without food reinforcement until it ceased to cause even the slightest salivation. If now, after the application of the differential cauldron, we try positive stimuli, it turns out that the salivary action of the latter undergoes regular changes.

Each time the differentiation cassette created a center of inhibition, the adjacent positive reflexes began to change as well. Consequently, inhibition goes beyond its focus and captures the neighboring cells of the analyzer, in this case, those on which the points of positive touches are projected.

Under the same conditions, the conditioned reflexes associated with positive wheelchairs change in different ways. Thus, the reflex associated with the nearest point (cassette 1) turned out to be completely inhibited. The reflex associated with the point located somewhat further away (cart 2) was only reduced. The reflexes associated with points located even further away not only did not experience inhibition, but even intensified. Consequently, irradiating inhibition has a stronger effect on the cells of the analyzer, the closer they are to the inhibitory focus.

Everyone who has played ball knows how easy it is to trick a partner by making a few tricks with the ball. After a series of such throws, the partner not only does not try to catch the ball, but does not even move from his place, does not change his position. The inhibition that occurred as a result of the extinction of the conditioned reflex to throw the ball spread to numerous nerve centers. This example also illustrates the irradiation of inhibition.

Inhibition concentration

After a wide irradiation comes concentration, inhibition concentration at the place of its origin. This process is also conveniently traced by the example of differential inhibition in the skin analyzer. The experiments were carried out in the same way as when observing irradiation, but positive reflexes to irritation of each area of ​​the skin were tested at different times after the end of the action of the inhibitory stimulus. With the help of this technique, one can see how the initially far-spread inhibitory state begins to concentrate, returning to the starting point.

When concentrated, inhibition passes in reverse order through all those points of the projection fields of the analyzers that it captured in its forward motion.

What is the braking process? There are two options. In the first case, the widespread inhibition dissipates, fades on the periphery, and the territory occupied by it gradually decreases. In the second case, the reverse deceleration wave rises to that place from where it spread. The latter is more probable, since, for example, the strengthening of differentiation is accompanied by an intensification of the inhibitory process.

Consequently, the concentration of inhibition is not associated with dissipation and weakening, but with its concentration and strengthening.

Speed ​​of irradiation and concentration of inhibition

Based on a number of experiments with a skin analyzer, it was possible to measure the rate of irradiation of the inhibitory state. It turned out that the process of irradiation of inhibition through the nerve cells of the cortex proceeds very slowly. Inhibition takes minutes to pass through the area of ​​the skin analyzer alone.

The absolute values ​​of the concentration time of the inhibitory process, as well as the time of its irradiation, strongly depend on the individual characteristics of the experimental animals, but their ratio turned out to be fairly constant in all the dogs tested. As a rule, irradiation occurs 4–5 times faster than subsequent concentration.

Irradiation and concentration of excitation

The experiment showing the irradiation of the excitatory process resembles in some respects the experiments described with the irradiation of inhibition.

The dog along the hind leg from the metatarsus to the pelvis at approximately the same distance from each other was glued five cassettes. A conditioned salivation reflex was developed in response to the action of the lowest cassette (cassette 1), which was reinforced by pouring acidified water into the dog's mouth. In the first test, other similar stimuli (cassettes 2, 3, 4, and 5) induced salivation. To develop differentiated reactions from wheelchairs, wheelchair 1 was repeatedly used with reinforcement, and the rest of the wheelchairs without reinforcement. Now only wheelchair 1 caused salivation, and the rest turned into brake signals.

After such preparation, they proceeded to the main part of the experiment. Turned on the positive treadmill 1 for 15 s, and immediately after it was turned off, the tether 2 was actuated. However, its action also caused salivation. This meant that the point of the skin analyzer, under the wheelchair 2, which is usually in a state of inhibition, immediately after the appearance of a focus of excitation in the point, under the wheelchair 1, was also in an excited state. In other words, the excitation from the point under the wheelchair 1 at that time spread to the point under the wheelchair 2. If you also test some other, more distant point of the skin analyzer, then you can judge the area of ​​​​such irradiation. Thus, radiating excitation gradually weakens as it moves away from the focus of its development (Fig. 2).

Rice. 2. Experiment with irradiation of excitation through the cortical cells of the skin analyzer:
1 - positive conditioned stimulus; 2, 3, 4, 5 - differentiating stimuli

Experiments have shown that the irradiation of excitation in the cerebral cortex occurs much faster than the irradiation of inhibition, and requires less than 1 s to propagate through the region of the skin analyzer.

Some time after a positive signal, the neighboring points of the analyzer again find themselves in the same braking state. This means that the wave of excitation has already managed to spread over the cortex and re-focus at the starting point.

Similar patterns can be observed in human life. The child was cauterized with iodine on the wound on his hand. First he jerked his hand away, then he began to wave it, then jump up and down, cry, shout. Excitation that arose in one point of the cortex spread to others. It covered vast areas of the cortex, subcortical centers.

In the process of learning any skill, a person first makes a large number of unnecessary movements, and only after a more or less long practice, his movements become economical, coordinated. Irradiation of excitation gives way to concentration, as a result of which excitation is constricted into certain areas.

Thanks to the irradiation of excitation, the animal can respond not only to the conditioned stimulus to which the conditioned reflex was developed, but also to similar stimuli. The cat found the mouse by its squeak and caught it. The squeak of the mouse became a conditioned stimulus. But will a cat react only to this sound? It turns out not. Thanks to the irradiation of excitation, she will respond to a lot of similar sounds: the squeak of chicks, the chirping of a grasshopper, etc. It is possible that some of them will be useful. Irradiation makes the conditioned reflex generalized, or, as they say, generalized. Only some time after the formation of this reflex, thanks to differential inhibition, the animal learns to distinguish true signals from false ones. Due to the concentration of excitation, the catch reflex becomes specialized.

Thus, both the process of excitation and the process of inhibition have the ability to irradiate and concentrate.

II. Consolidation of knowledge

Generalizing conversation in the course of learning new material.

III. Homework

To study a paragraph of the textbook (the concepts of irradiation and concentration of nervous processes, irradiation and concentration of inhibition and their speed, irradiation and concentration of excitation).

Lesson 2-3. INDUCTION OF NERVOUS PROCESSES

Equipment: tables, diagrams and drawings illustrating the processes of irradiation and concentration of excitation and inhibition, as well as the processes of positive and negative induction, the dominant phenomenon.

DURING THE CLASSES

I. Knowledge Test

Card work

Prove that in the early stages of the development of a conditioned reflex, irradiation of excitation occurs in the cortex of the hemispheres big brain.

1. General characteristics of the processes of irradiation and concentration of excitation and inhibition.
2. Characteristics of the irradiation of inhibition.
3. Characteristics of concentration inhibition.
4. Characteristics of irradiation and excitation concentration.
5. Rate of irradiation and concentration of inhibitory and excitatory processes.

II. Learning new material

Positive induction of nervous processes

The movement of the main processes of GNI is determined not only by the properties of irradiation and concentration, but also by the properties of their mutual induction. by induction(from lat. induction- excitation) is the property of each of the main nervous processes to cause around itself and after itself the opposite process.

The phenomenon in which the process of inhibition gives rise to the process of excitation is called positive induction.

The phenomenon of positive induction was revealed in special experiments using an example connected with differential inhibition. Thus, a conditioned alimentary salivation reflex was developed in a dog, in which the signal was irritation of the skin of the front paw with a wheelchair. Another cassette was installed on the rear leg. It was used without reinforcement, so that it soon acted as an inhibitory differentiation stimulus. There was no salivation upon activation of the differential kazakh, but the positive stimulus tested immediately after it gave a sharply enhanced reflex.

Measurement of the strength of the conditioned reflex by the amount of saliva reveals that inhibition at the point of the hind paw increased the conditioned excitation at the point of the fore paw by almost 50%. Consequently, in this case there was a positive induction from the focus of inhibition to the focus of excitation.

We encounter positive induction quite often in life. In a baby who is tired during the day, braking processes begin to develop in the cerebral cortex, since this department has the least endurance. Inhibition in the cortex, according to the law of positive induction, causes excitation of the subcortical centers, in particular those with which emotions are associated. The child begins to either have fun or be capricious. Often positive and negative emotions replace each other: the child cries, then starts laughing again.

The same thing happens with an intoxicated person. Alcohol causes narcotic inhibition in the cortex, which leads to excitation of the subcortical centers due to positive induction. Emotional reactions intensify, the person goes into a state of painful gaiety - euphoria, which is often replaced by severe melancholy. Behavior becomes abnormal, often aggressive. A critical attitude to the situation is lost, an intoxicated person cannot assess the degree of risk. Everything seems to him accessible and possible. This makes a drunk person socially dangerous.

Negative induction of nervous processes

The process by which excitation causes inhibition is called negative induction.

The phenomenon of negative induction can be demonstrated in the following experiment. The dog has a conditioned food reflex to the metronome with a frequency of 120 beats per minute. To this positive stimulus, a metronome differentiation with a frequency of 60 beats per minute was developed. As you know, differentiation is very easy to destroy if you begin to accompany the differentiation stimulus with reinforcement. And indeed, after a few times a metronome with a frequency of 60 beats per minute was used with reinforcement, he himself began to induce salivation. This is a simple and trouble-free way to destroy the brake focus.

After the destruction of differentiation, one metronome with a frequency of 120 beats per minute is used with reinforcement. As a result, a 60 beats per minute metronome, which had just elicited salivation, followed immediately loses its effect. At the same time, differentiation is restored, which is associated with the appearance of a focus of excitation. This focus negatively induced, i.e. inhibited the cells of the metronome point with a frequency of 60 beats per minute, and the induced inhibition enhanced the differentiation residues.

Let us give an example of negative induction from a person's life. The child was given soup, he began to eat it with appetite, but then the TV was turned on, and the child froze with a raised spoon. A familiar external inhibition occurred: a strong excitation of the visual centers slowed down the food center.

Dominant and its role in mental processes

Behavior is largely determined by needs. In the event that one of the needs develops into a strong desire, it can subjugate everything else. The famous physiologist A.A. Ukhtomsky discovered that in the nervous system, in particular in brain, there may be strong foci of temporary excitation. These temporarily dominant foci of excitation in the central nervous system, which have increased excitability to all stimuli that come into them and are capable of exerting an inhibitory effect on the activity of other nerve centers, were called dominants(from lat. dominantis- dominating).

Under the conditions of the dominant, conditioned reflex connections are easily formed between the signal stimulus and the unconditioned reinforcement. Dominants are able not only to exert intense negative induction on neighboring areas, as a result of which a significant inhibition of those fields that do not belong to the dominant is achieved, but also excitations caused by stimuli that are not related to the dominant change their usual direction. Nerve impulses, instead of moving along their traditional path, go towards the dominant focus. The dominant, as it were, attracts them and intensifies at their expense.

For example, if after developing a conditioned chewing reflex in a guinea pig to tapping on the table, instead of tapping, say any phrase, the animal will begin to chew. The guinea pig will start chewing when it hears a voice and stop chewing when you stop talking. Any irritation - auditory, tactile, visual - will cause her chewing movements without prior development. When developing a food conditioned reflex, a dominant was created in a guinea pig. New stimuli (the voice of a person, etc.) now, without any development, turn out to be associated with food arousal. This happens because the nerve impulses that appeared under the influence of these stimuli change their usual path, radiating towards the dominant focus of excitation, as if attracted by it. They enhance dominant excitation, which we see by the appearance of a chewing reaction.

A.A. Ukhtomsky believed that entire systems of reflexes could dominate. The dominant underlies such mental processes as attention, concentration, the ability to volitional efforts. Thanks to the dominant, a person completely “goes” into work, nothing distracts him, he does not hear when he is addressed. The focus is on what he is doing. An alcoholic in a state of binge cannot think of anything but drinking. Often he is unable to control his actions and becomes dangerous to others.

However, in some cases, the appearance of long-lasting foci of dominant excitation can cause various mental illnesses. This kind of stagnant foci of pathological excitation was observed by I.P. Pavlov. They are one of the reasons why mentally ill people misjudge events and react abnormally to them.

Functional mosaic in the higher parts of the nervous system

The interaction of radiating and induced nervous processes creates an unusually complex and changing from moment to moment their balancing and territorial demarcation. As a result, excitation and inhibition form a fractional pattern of a moving mosaic that continuously changes its shape (Fig. 3).

Rice. 3. Redistribution of foci of activity in the cerebral cortex of a rabbit during the development of a long conditioned reflex to visual stimulation

At one time, I.P. Pavlov talked about what a wonderful picture of flashing and fading, continuously intermittent flickering we would see on the surface of the brain if its excited points were luminous. This became possible when studying the movement of nervous processes in the cortex of the cerebral hemispheres using the technique electroencephaloscopy. The electroencephaloscope makes it possible to observe the mosaic of the electrical activity of the cerebral cortex with simultaneous recording of 100 of its points and reproduces on the TV screen continuously emerging and changing moving pictures that are recorded by filming. Such a "TV" of the brain significantly expands the possibilities of an objective study of the spatial dynamics of the activity of the cortex during conditioned reflex activity.

III. Consolidation of knowledge

Laboratory work No. 4. "Studying the phenomenon of mutual induction of excitation and inhibition processes"

Equipment: drawings of dual images.

PROGRESS

1. Consider the drawing "vase - two profiles" (Fig. 4). Find two black profiles on it, facing each other, and a white vase (it is located between the profiles).

2. Why, when the vase is visible, the profiles disappear, and when we see the profiles, the image of the vase disappears? (The reason is that one of the competing images inhibits the appearance of the second, i.e. there is a negative induction: excitation induces inhibition).

3. Look at the picture “vase - two profiles” until the images begin to replace each other: either a vase or two profiles will be visible. Explain this phenomenon. ( When we see a vase, the complex of nerve connections that perceive it is excited, and the complex of connections that perceive the two profiles is inhibited. However, according to the law of successive induction, after one process, the opposite one appears, and excitation is replaced by inhibition in one complex of nerve connections, and inhibition is replaced by excitation in another.).

4. Consider the picture "young and old women" (Fig. 5). Explain the reason for changing images.

5. Conclusion: what law did you encounter when doing laboratory work?

IV. Homework

Study the textbook paragraph (positive and negative induction, dominant phenomenon, functional mosaic in the network of neurons).

Lesson 4-5. HUMAN DREAM AND ITS CHARACTERISTICS. THEORIES OF SLEEP. DREAMS

Equipment: tables, diagrams and drawings illustrating the processes of positive and negative induction, the dominant phenomenon, the stages of sleep.

DURING THE CLASSES

I. Knowledge Test

Card work

1. Give examples of the manifestation of the law of mutual induction of excitation and inhibition.
2. What is the significance of the dominant phenomenon in a person's life?

Oral knowledge test on questions

1. The law of mutual induction of nervous processes. positive induction.
2. Negative induction.
3. The phenomenon of the dominant.
4. Functional mosaic in the higher parts of the nervous system.

II. Learning new material

Human sleep and its physiological significance

Natural phenomena are often strictly periodic: the seasons, the phases of the moon, day and night change. Living organisms have adapted to these changes. The active behavior of people is mainly confined to the daytime hours. At night, sleep sets in, and tired people rest during the night.

Dream - periodically occurring physiological state in vertebrates and humans, characterized by an almost complete absence of reactions to external stimuli, a decrease in the activity of a number of physiological processes.

About a third of his life a person spends in a dream. The alternation of sleep and wakefulness is a necessary condition for the life of the human body. Without sleep, life is impossible. So, in the experiment, dogs lived without food for 20–25 days and lost 50% of their weight, and without sleep for 10–12 days, although their weight decreased by only 5–13%.

How much time do you need to sleep? It depends on age. The newborn sleeps almost all the time, he is awake only 2-3 hours a day; a six-month-old baby sleeps about 14 hours, a one-year-old - 13 hours. At the age of four, children sleep up to 12 hours a day, at a seven-year-old - 11 hours, at a ten-year-old - 10 hours. Fifteen-year-olds should sleep 9 hours a day, and starting from 17-18 years, the duration of sleep can be an average of 7-8 hours. In old age, they usually sleep less. However, sleep duration can vary from person to person. From the biography of Peter I it follows that he slept no more than 5-6 hours, and that was enough for him. Numerous cases are also described when a person was content with an even more limited sleep time.

Constant lack of sleep can cause headaches, increased fatigue and contribute to memory deterioration, the appearance of nervous and other diseases. Prolonged sleep is just as harmful as prolonged wakefulness. Sleep cannot be stocked up for future use.

The brain is kept awake by impulses coming from the body's receptors. With the termination or sharp restriction of their entry into the cortex, sleep develops. Sleep also develops when cortical cells are exposed to prolonged or excessive force of stimuli. At the same time, inhibition develops in the cells of the cortex, which has a protective value. It provides the cortex of the cerebral hemispheres with the conditions for restoring performance during sleep.

At present, the existence of formations in the brain stem that influence the onset of wakefulness and sleep has been established. The reticular formation has a significant influence on wakefulness, and the thalamus has a significant influence on sleep.

About physiological significance of sleep There are different assumptions that can be conditionally reduced to the following groups.

Restoration of the specific metabolism of brain nerve cells, which ensures its full activity in the waking state. I.P. Pavlov believed that the "exhaustion" of cortical cells that occurs during a hard day's work causes sleep inhibition during which their performance is restored. According to Pavlov, “sleep is a general inhibition that occurs when brain cells need rest.” Sleep protects the brain from overstrain, in a dream the information accumulated during the day is processed, new ideas are born.

Adaptation to adverse working conditions. Diurnal animals become helpless at night, as they do not navigate in the dark and can become easy prey for nocturnal predators. In turn, the latter find themselves in a similar position during the day. Sleep provides not only rest, but also security through protective immobility in a secluded place. This is one of the types of instinctive adaptive behavior.

Streamlining the processes of processing and storing information. The significance of sleep for the state of memory is understood in two ways. A number of scientists believe that the “unnecessary” information accumulated during the day is being eliminated, and memory is “disintegrating”. This preparation of the brain for the perceptions of the next day is compared to erasing information in the memory cells of a computer. Others, on the contrary, believe that during sleep there is a consolidation of memory, a transition from short-term to long-term. There are also assumptions about the processing of information that the brain did not have time to process during the day.

Restoring the consistency of the temporal flow of body functions. Countless biochemical reactions are built into a complex system for providing the functions of cells, tissues and organs. Coordination in time of these interrelated, periodically changing functions is a necessary condition normal life organism.

Thus, sleep is a protective adaptation of the body, preventing overwork of the nervous system.

Characteristics of human sleep stages

According to the electrical activity of the brain, night sleep can be divided into two periods (phases):

slow wave(slow sleep) ;

paradoxical, or fast wave(rapid sleep).

Sleep time is differentiated into slow and fast sleep, mainly for plastic recovery processes, processing of accumulated information and consolidation of long-term memory.

During sleep, the physiological activity of the body changes: muscles relax, skin sensitivity, vision, hearing, smell decrease, conditioned reflexes are inhibited. Breathing during sleep is rare, blood pressure, heart rate are reduced. But sleep is not an inactive state of the nervous system. During sleep, electrical discharges occur in neurons, but the nature of the electrical activity changes. Some reactions in a sleeping person intensify: the skin vessels dilate, the face turns red, the tone of some muscles increases, the secretion of the gastric and intestinal glands increases, absorption is more intense, many synthetic processes are activated.

The dynamics of the electrical activity of the brain during the development and course of sleep in humans has been studied by many researchers. A classification of sleep stages was proposed based on changes in the level of consciousness and the shape of the electroencephalogram. The main stages in the development of natural sleep in humans include(Fig. 6) :

stage A- initial for falling asleep. The neurons of the brain are dominated by electrical waves with a frequency of 8-12 oscillations per second, which is typical for a state of calm wakefulness;

stage B- drowsiness. Low-voltage oscillations of different frequencies predominate;

stage C- superficial sleep. Spindle-shaped groups of oscillations with a frequency of 12-14 oscillations per second and separate slow waves appear in the electrical activity of the brain;

stage D- deepening sleep. Giant (200–300 μV) slow waves (1–3 oscillations per second) appear;

stage E- deep sleep, continuous rows of slow waves. Slow sleep is accompanied by a decrease in breathing, pulse, muscle relaxation. It is characterized by dreams and imaginings;

stage P (paradoxical)- deep sleep, accompanied by shudders, movements of the eyeballs, dreams. In the encephalogram, waves appear that resemble attention reactions during wakefulness, but at a higher frequency. Awakened in this state, people noted that they had dreams. A person experiencing paradoxical sleep disorders is hard.

stages D and E referred to as the period of slow sleep, and the stage R- as a period of paradoxical sleep. During the night, the depth of sleep can change many times. Accordingly, the stages of sleep will replace each other when leaving deep sleep in the reverse order, and the next time it deepens, in the usual sequence. Therefore, periods of slow and fast (paradoxical) sleep alternate many times. A typical night's sleep consists of 4-6 completed cycles, each of which begins with non-REM sleep and ends with REM sleep. The duration of the cycle is from 60 to 90 minutes. In a normal 8-hour night of sleep, non-REM sleep takes a total of 6.5 hours, and REM sleep takes more than 1.5 hours.

Stimuli to awaken from sleep can be: bright light, noise, signals from internal organs (a hungry stomach, a full bladder), increased hormonal activity and metabolism.

Theories of sleep

With the accumulation of factors and observations of human and animal sleep, different theoretical ideas about its nature arose. Let's get acquainted with some of them.

1. Hypnotoxin Theory. The well-known refreshing effect of sleep suggested that during this time the body is freed from the toxic metabolic products accumulated during daytime activity, which cause sleep inhibition of brain nerve cells. Recently, the involvement of humoral factors in the development of sleep has been shown. From the blood of an animal that fell asleep as a result of irritation of certain areas of the thalamus, was obtained delta sleep peptide, the introduction of which caused sleep.

2. Theory of sleep centers. This theory originates from clinical observations of patients with encephalitis, which causes lethargic sleep. In these patients, a certain part of the brain stem turns out to be inflamed, which has come to be regarded as the center of sleep. The assumption that sleep is caused by excitation of special centers was supported in experiments with stimulation of the structure of the diencephalon, under the influence of which the cat was put into a characteristic sleep position and fell asleep (Fig. 7). However, further studies showed that such a result can be obtained by stimulating various brain structures in a certain mode of stimulation, which contradicted the idea of ​​a nerve center that should have a certain localization. In addition, clinical observations have shown that sleep pathology is not associated with a specific localization of brain damage. At the same time, the question of sleep centers is of considerable interest.

3. Theory of conditional inhibition. When studying conditioned reflexes, representatives of the school of I.P. Pavlova, it was found that the production various kinds conditioned inhibition can lead to sleep. This was observed during the development of differentiations, retardation, and conditioned inhibition. Similar circumstances cause drowsiness in humans. From this it was concluded that "internal inhibition of conditioned reflexes and sleep are one and the same process."

4. Theory of deafferentation of sensory systems. The basis for this theory was the facts of the development of deep sleep in animals with the main pathways for information to the cerebral hemispheres turned off (by cutting the brain stem at a level preceding the midbrain). This theory is supported by a description of a patient who retained only one eye and one ear of all his senses (this patient fell asleep as soon as they were closed), and experiments with surgically turning off a dog's sight, hearing and smell, as a result of which it almost all the time sleeping.

5. Theories of nonspecific regulators of sleep–wakefulness. The ascending activating system of the reticular formation of the midbrain plays a special role in the nonspecific regulation of the functional state of the higher parts of the brain. Her irritation causes an awakening reaction, increases the excitability of the cerebral cortex. Reducing the influence of the reticular formation on the cortex leads to the development of sleep. This explains the deep non-awakening sleep after the transection of the brain stem in front of the midbrain.

To be continued

Rice. 7. A-Irradiation of nervous processes; B - concentration of nervous processes.

Without movement and interaction of the main nervous processes - excitation and inhibition- Higher nervous activity is impossible. The movement of nervous processes is a natural phenomenon. IP Pavlov discovered two basic laws of motion of nervous processes in the cortex: the law of irradiation and concentration and the law of mutual induction.

The movement of nervous processes is a natural phenomenon. I. P. Pavlov discovered two basic laws of motion of nervous processes in the cortex: the law of irradiation and concentration and the law of mutual induction

Excitation or inhibition of the cortex hemispheres

Excitation (or inhibition), having arisen at any point in the cerebral cortex, does not remain in it, but first irradiates, i.e., spreads to the nearest nerve cells, sometimes captures vast areas of the cortex (Fig. 7, A). After some time, the opposite phenomenon of concentration is observed, i.e., the concentration of the nervous process in the place where it arose (Fig. 7, B). Since the cells of the cortex may be in a different functional state, the irradiation of a nervous process may meet with resistance from the opposite nervous process, irradiating from another point in the cortex. Meeting opposite processes causes them to fight. A wave of irradiating excitation “drives away” the inhibitory process from the nearest cells to distant points of the cortex, but if inhibition becomes strong enough, which happens when the conditioned stimulus is not reinforced, it, spreading, in turn “drives” the excitation to the place of its origin. Very convincingly the phenomenon of irradiation and concentration of nervous processes is proved by the well-known experiments in the laboratories of I. P. Pavlov with irritation of the skin analyzer of a dog by means of treadmills.

The movement of nervous processes in the cerebral cortex has a number of patterns.

Excitation spreads and concentrates much faster than inhibition. The speed of its movement is measured in seconds and fractions of seconds. Speed movement of the braking process measured in minutes, and the concentration of inhibition occurs 4-5 times slower than irradiation. It was further established that movement of nervous processes in the cortex depends on the strength of the stimuli that caused them, on the functional state of the cerebral cortex at the time of the experiment, and on the balance of excitation and inhibition, which, in turn, depends on the age and individual typological characteristics of the organism.

Irradiation of excitation

The phenomenon of generalization of communication conditions, which was discussed above, is explained irradiation of excitation along the cortical part of the analyzer, and sometimes along the nearby cells of other analyzers. Therefore, a non-specific, generalized response of the body to similar stimuli arises. Generalization of excitation, according to IP Pavlov, has positive and negative values. On the one hand, this phenomenon is biologically justified. The agents to which natural conditioned reflexes are formed in animals constantly fluctuate. Thus, the voice of a predator, which serves as a danger signal for the prey animal, fluctuates in height, strength, and composition depending on the tension of the vocal apparatus, distance, and resonance. The smell of a plant, which serves as a signal of a food conditioned reflex to a herbivore, varies depending on air humidity, distance, proximity to other smells, and other conditions. Without generalization, the animal would not be able to attribute all changes in the stimulus to one and the same agent and act in accordance with its role.

The negative value of generalization lies in the fact that sometimes, with a wide irradiation of excitation through the cells of the cortex, agents remotely similar to the main signal are included in the scope of generalization; and this leads to gross indistinction, an undesirable confusion of actions.

The phenomenon of generalization of the conditioned connection is the phenomenon of the simplest cortical synthesis.

Generalization of conditioned reflexes is followed by their specialization

That is, a distinct isolation of the signal stimulus from the mass of agents similar to it. She explains concentration of nervous processes in certain points of the cortex, which is caused by differential inhibition. The phenomenon of specialization of conditional connection is the phenomenon of cortical analysis. Specialized conditioned reflexes can interact with each other, forming complex functional systems. Such a secondary synthesis is higher in its level than the primary generalization. It is based on selective generalization. The analytical and synthetic activity of the cortex develops in an animal in the process of complicating its connection with the outside world, in a person - in the process of training and education.

The study of the patterns of cortical inhibition made it possible to reveal the physiology of sleep. Sleep, according to the teachings of I. P. Pavlov, has a conditioned reflex nature and arises as a result of a wide irradiation of inhibition, which covers the entire cortex of the hemispheres and descends lower - into the subcortex and even the midbrain. Sleep inhibition can be caused by various reasons: a decrease in the level of efficiency of cortical cells as a result of their prolonged and intense functioning, limitation of stimuli entering the cortex from outside (a long stay in the dark, in silence with immobility or rhythmic movements of the body can cause sleep even if a person is not tired) and the habit of falling asleep in certain time. In an experimental setting, sleep can be induced by prolonged, continuous action of some stimulus without its reinforcement by an unconditioned one. In this case, extinctive inhibition, irradiating, passes into sleep.

Sleep inhibition spreads through the cortex with uneven speed and force.

Some groups of nerve cells in which persistent process of excitation may remain uninhibited even during sleep. So-called "guard points" are formed, which leads to an immediate awakening under the influence of certain signals, even weak ones. This is the dream of a nursing mother, who immediately wakes up to faint sounds coming from the baby (groaning, shortness of breath, slight movement of the baby).

The reasons for sleep may be different. Sleep can be induced by a sharp restriction of external stimuli, as well as by electrical stimulation of special subcortical centers. Sleep is necessary for the body to restore the efficiency of nerve cells.

Rice. 8. Simultaneous induction: A - positive; B - negative

Excitation and inhibition mutually induce, i.e., they cause and reinforce each other. Excitation causes inhibition and vice versa. The stronger the excitation, the stronger will be the inhibition caused by it. There are two types of induction: positive and negative, each of which can be simultaneous and sequential. If the initial process is excitation, which by induction causes inhibition, this is negative induction (Fig. 8, B), and if inhibition causes excitation, this is positive induction (Fig. 8, L), with simultaneous induction, the nervous processes are located in different points of the cortex and exist together, but with sequential induction (Fig. 8, A, B) nervous processes replace each other in the same point of the cortex.1 Let us give examples of various types of inductive relations in the cortex.

With a high concentration of auditory attention, a person sits motionless, does not notice anything that does not relate to the object of his attention. Excitation process concentrated in certain cortical cells of the auditory analyzer, and inhibition is temporarily diffused around them. This is a simultaneous negative induction. But the sounds that the person listened to (for example, the speech of the teacher) stopped. Now, in the working cells of the auditory analyzer, excitation is replaced by inhibition. This is sequential negative induction. If students in a physics lesson solved problems on their own, and then the teacher invited them to observe a demonstration of physical experience, then such a change in mental activity entails temporary rest, inhibition of the working cells of certain brain fields after their prolonged excitation. This is also consistent negative induction.

An example of simultaneous positive induction is the phenomenon of contrast in perception.

So, the light gray background around the black square appears white in contrast. There is no light irritation from the black square. In the corresponding cortical cells of the visual analyzer, an inhibitory process occurs, which, by induction, enhances the excitation process that arose in neighboring cells from the perception of a light gray background. The illusion of a brighter illumination of this background is created than it actually is. Second example. The monotonous quiet speech of the teacher in the lesson, not accompanied by a demonstration of visual aids or experiments and not containing vivid descriptions, very quickly tires schoolchildren, especially children younger age. Their attention becomes distracted. AT tired nerve cells In the speech-auditory area of ​​the cortex, a process of inhibition occurs, which, by induction, enhances the excitation of neighboring nerve cells of the visual, auditory and motor analyzers, caused by the action of weak stimuli: the child now notices the occasional creak of the desk, the rustle of paper from behind, coughing; examines his hands and objects lying on the desk, sitting in front of the students; sorts through any familiar things in his pockets or in his desk, etc. Orienting reflexes to extraneous weak stimuli are amplified precisely because the main stimulus - the teacher's voice - caused persistent inhibition in the speech-auditory area of ​​the cortex. This is a simultaneous positive induction. An example of sequential positive induction is the same fact with a boring lesson: after a long forced sitting in the classroom, even disciplined children and teenagers make quite a noisy break. long inhibition of motor reactions replaced by increased physical activity. Inductive relationships of the basic nervous processes also exist between the cortex and the nearest subcortex. With strong emotions (anger, fear, despair), the excited subcortex induces inhibition of cortical nerve connections, primarily secondary signals. This explains the lack of reasonableness of some actions of an emotionally excited person. The opposite is also possible.

The activity of the cerebral cortex is subject to a number of principles and laws. The main ones were first established by I.P. Pavlov. At present, some provisions of the Pavlovian teaching have been clarified, developed, and some of them have been revised. However, in order to master the basics of modern neurophysiology, it is necessary to become familiar with the fundamental provisions of Pavlov's teaching.

Analytical-synthetic principle of higher nervous activity.

As established by I.P. Pavlov, the main fundamental principle of the cerebral cortex is the analytic-synthetic principle. Orientation in environment associated with the isolation of its individual properties, aspects, features (analysis) and the association, the connection of these features with what is beneficial or harmful to the body (synthesis). Synthesis is the closure of connections, and analysis is an increasingly subtle separation of one stimulus from another.

The analytical and synthetic activity of the cerebral cortex is carried out by the interaction of two nervous processes: excitation and inhibition. These processes are subject to the following laws.

The law of irradiation of excitation. Very strong (as well as very weak) stimuli with prolonged exposure to the body cause irradiation - the spread of excitation over a significant part of the cerebral cortex.

Only optimal stimuli of medium strength cause strictly localized foci of excitation, which is the most important condition for successful activity.

The law of concentration of excitation. Excitation that has spread from a certain point to other areas of the cortex, over time, is concentrated in the place of its primary occurrence.

This law underlies the main condition of our activity - attention (concentration of consciousness on certain objects of activity).

When excitation is concentrated in certain areas of the cerebral cortex, its functional interaction with inhibition occurs, and this ensures normal analytical and synthetic activity.

The law of mutual induction of nervous processes. On the periphery of the focus of one nervous process, a process with the opposite sign always occurs.

If the process of excitation is concentrated in one area of ​​the cortex, then the process of inhibition inductively arises around it. The more intense the concentrated excitation, the more intense and widespread the process of inhibition.

Along with simultaneous induction, there is a successive induction of nervous processes - a successive change of nervous processes in the same parts of the brain.

Only a normal ratio of excitation and inhibition processes provides behavior that is adequate (corresponding) to the environment.

The imbalance between these processes, the predominance of one of them causes significant disturbances in the mental regulation of conduction.

So, the predominance of inhibition, its insufficient interaction with excitation leads to a decrease in the activity of the organism. The predominance of excitation can be expressed in disorderly chaotic activity, excessive fussiness, which reduces the effectiveness of activity. The process of inhibition is an active nervous process. It limits and directs the process of excitation in a certain direction, promotes concentration, concentration of excitation.

Braking is external and internal. So, if some new strong stimulus suddenly acts on the animal, then the previous activity of the animal at the moment will slow down. This is external (unconditional) inhibition. In this case, the emergence of a focus of excitation, according to the law of negative induction, causes inhibition of other parts of the cortex.

One of the types of internal or conditioned inhibition is the extinction of the conditioned reflex if it is not reinforced by an unconditioned stimulus (extinguishing inhibition). This type of inhibition causes the cessation of previously developed reactions if they become useless under new conditions.

Inhibition also occurs when the brain is overexcited. It protects nerve cells from exhaustion. This type of braking is called protective braking.

The analytical activity of the cerebral cortex, the ability to distinguish objects and phenomena similar in their properties, is also based on the internal form of inhibition. So, for example, when an animal develops a conditioned reflex to an ellipse, it first reacts to both the ellipse and the circle. There is a generalization, a primary generalization of similar stimuli. But, if the presentation of the ellipse is constantly accompanied by a food stimulus and the presentation of the circle is not reinforced, then the animal gradually begins to separate (differentiate) the ellipse from the circle (the reaction to the circle slows down). This type of inhibition, which underlies analysis, differentiation, is called differential inhibition. It clarifies the actions of the animal, makes it more adapted to the environment.

What conditions are necessary for the development of a conditioned reflex?

How does reflex inhibition occur?

Multiple repetition and the occurrence of a temporary connection

As a result of systematic non-reinforcement of actions

1. How does the nervous system regulate the work of organs?

In the neurons of the nervous system, there are two main oppositely directed processes: excitation inhibition Excitation stimulates the organ to work, as if including it in it, inhibition slows down or stops this work. Thanks to these processes, the work of organs is regulated. This regulation is multilevel.

2. What is the essence of multilevel regulation? What was the significance of the discovery of I.M. Sechenov central braking?

As studies by I.M. Sechenov, the lower centers work under control higher centers. They can inhibit many unconditioned reflexes (central inhibition) or enhance them. It is the centers of the cerebral cortex that send inhibitory signals to the spinal cord, and we do not withdraw our hand when we take blood for analysis.

3. What types of inhibition were discovered by I.P. Pavlov?

Continuing the research of I.M. Sechenov, I.P. Pavlov showed that there is conditional and unconditional inhibition.

4. Give examples of unconditional and conditional inhibition.

Unconditional, or congenital, inhibition. Imagine that you are doing something, like reading a book, and you are invited to dinner. You were presented with two incentives, the most important one is selected from them. If the book is very interesting, you may not hear the words addressed to you, since stimuli of little importance to you affect the inhibited areas of the cortex. There will be a different choice if you are hungry and the book is boring. Then the old activity will be inhibited and a new one will begin. Thanks to unconditional inhibition, the choice of activity is possible: with the beginning of one activity, another automatically stops (or does not start). Conditional or acquired inhibition. Conditioned inhibition includes, for example, the extinction of a conditioned reflex. If the conditioned signal is left without reinforcement, then the conditioned reflex will soon fade away, and with prolonged non-reinforcement it can turn into a negative (inhibitory) conditioned connection. Thanks to these inhibitory connections, animals and humans learn to distinguish between similar stimuli. If the dog is fed after one call and not given food after two, then salivation will occur only after one call (after two it will not). Of course, this won't happen right away. At first, saliva will be separated into both stimuli, and only after a long training the animal will learn to correctly distinguish between signals.

5. In what cases is a negative (inhibitory) conditional relationship formed between a signal and behavior?

Conditioned inhibition is developed in cases where the conditioned reflex is not reinforced by the vital important event, about which the conditioned signal warned. Thanks to conditioned inhibition, it is possible to distinguish important signals from stimuli similar to them. IP Pavlov discovered the law of mutual induction: excitation in one center causes inhibition in a competing center, and vice versa. There is also sequential induction: excitation in one center after a while is replaced by inhibition, and vice versa.

6. What is a dominant and how does it manifest itself?

The behavior of animals and humans is regulated by needs. They retreat for a while after they are satisfied, then reappear. A.A. Ukhtomsky discovered the phenomenon of dominance: the emergence in the brain of a powerful temporary focus of excitation caused by some urgent need. Thanks to the dominant, the formation of a temporary connection between the future signal and the need that has arisen is facilitated, which favors the development of a conditioned reflex.

7. Give examples of the manifestation of the law of mutual induction of excitation and inhibition.

The light gray background around the black square appears white in contrast. There is no light irritation from the black square. In the corresponding cortical cells of the visual analyzer, an inhibitory process occurs, which, by induction, enhances the excitation process that arose in neighboring cells from the perception of a light gray background. The illusion of a brighter illumination of this background is created than it actually is. Second example. The monotonous quiet speech of the teacher in the lesson, not accompanied by a demonstration of visual aids or experiments and not containing vivid descriptions, very quickly tires schoolchildren, especially young children. Their attention becomes distracted. In the tired nerve cells of the speech-auditory area of ​​the cortex, an inhibition process occurs, which, by induction, increases the excitation of neighboring nerve cells of the visual, auditory and motor analyzers, caused by the action of weak stimuli: the child now notices the occasional creak of the desk, the rustle of paper from behind, coughing; examines his hands and objects lying on the desk, sitting in front of the students; sorts through any familiar things in his pockets or in his desk, etc. Orienting reflexes to extraneous weak stimuli are amplified precisely because the main stimulus - the teacher's voice - caused persistent inhibition in the speech-auditory area of ​​the cortex. This is a simultaneous positive induction. An example of sequential positive induction is the same fact with a boring lesson: after a long forced sitting in the classroom, even disciplined children and teenagers make quite a noisy break. Prolonged inhibition of motor reactions was replaced by increased motor activity. Inductive relationships of the basic nervous processes also exist between the cortex and the nearest subcortex. With strong emotions (anger, fear, despair), the excited subcortex induces inhibition of cortical nerve connections by induction. This explains the lack of reasonableness of some actions of an emotionally excited person. The opposite is also possible.

When closing and opening the circuit, the current is not established instantly. The deceleration effect is determined by the inductance of the circuit. Let's find the dependence when opening and closing the circuit.

P When the circuit is opened, the current decreases from the value
to zero and at the same time emf arises. self-induction
, which counteracts the decrease in current. At each moment in time, the current in the circuit is determined by Ohm's law:

.

Integrating the equation from before , we get:

,

where
- a constant having the dimension of time is called the relaxation time.

The more , the slower the current drops. During the current in the circuit decreases in times (approximately 3 times) (see dependence 1 in the figure).

.

Explore on your own.

The phenomenon of mutual induction. Mutual inductance. Ems of mutual induction.

E If two electrical circuits are close, they can influence each other. Such circuits are called inductively coupled. Let's consider two such contours (see figure). If a current is passed through the first circuit then the magnetic flux coupled to the second circuit will be proportional to the current , and will also depend on the mutual orientation of the contours, their geometric dimensions, the number of turns, and the magnetic properties of the medium. You can write:

.

Here the coefficient
called mutual inductance second circuit depending on the first. Reversely, if you pass the current through the second circuit, then for the magnetic flux coupled to the first circuit, we can write:

.

For linear media, the coefficients
and
are equal to each other:

.

Mutual inductance or inductance is measured in henries (H).

Mutual inductance
numerically equal to the magnetic flux coupled to one of the circuits, with a unit current in the other circuit. Mutual inductance depends on the shape, size and mutual orientation of the circuits, the magnetic permeability of the medium.

For example, the mutual inductance of two coils with a common core is:

,

where - the volume of the core, and - the number of turns per unit length of the generatrix of the core for the first and second coils.

D let's provide it. Let current flow on the first coil (see picture). For a sufficiently long coil, neglecting edge effects, we assume that the magnetic field in the core is uniform:

.

The magnetic flux coupled to the second coil will then be equal to:

Where does the expression for
, considering that
is the length of the core.

Note that the resulting relation for
is approximate and can be represented differently:

,

where and is the inductance of the coils.

E If an alternating current is passed through one of the circuits, then an induction current will appear in the second in accordance with Faraday's law.

For example, if in the first circuit
, then the magnetic flux coupled to the second circuit will change over time
and emf will appear in it. induction.

.

At
:

.

Obviously,
.

The emf that occurs in the circuits is called emf mutual induction.

Direction of currents and emf mutual induction is determined by the Lenz rule (see figure)

The resulting inductive current in the second circuit
their magnetic field hinders growth magnetic flux from the first loop.

The resulting inductive current in the second circuit with its magnetic field prevents the reduction of the magnetic flux from the primary circuit.

The change in currents in inductively coupled circuits in linear media is described by Ohm's law:

where
- emf sources in circuits 1 and 2,
- circuit inductance,
- mutual inductance of the circuits.

Note that the effect of transformers that serve to convert currents and voltages is based on the phenomenon of mutual induction.

R Let's consider the idling of the transformer. This is the case when the secondary winding of the transformer is not loaded (see figure). In this case, you can write:

.

because
.

Neglecting the resistance of the primary winding of the transformer
, we estimate the voltage on the secondary winding:

.

Transformers are used to increase or decrease voltage. For currents in the transformer windings, an inversely proportional dependence on the number of turns is observed:

.

Justify yourself.