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

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

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

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

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

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

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

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

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

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

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

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

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

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

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I. P. Pavlov divided all reflex reactions of the body to various stimuli into two groups: unconditioned and conditional.
Unconditioned reflexes are innate reflexes inherited from parents. They are specific, relatively permanent and are carried out by the lower parts of the central nervous system - the spinal cord, brain stem and subcortical nuclei of the brain.

Unconditioned reflexes (for example, sucking, swallowing, pupillary reflexes, coughing, sneezing, etc.) are preserved in animals lacking large hemispheres. They are formed in response to the action of certain stimuli. So, the salivation reflex occurs when food stimulates the taste buds of the tongue. The resulting excitation in the form of a nerve impulse is carried along the sensory nerves to the medulla oblongata, where the center of salivation is located, from where it is transmitted along the motor nerves to the salivary glands, causing salivation. On the basis of unconditioned reflexes, the regulation and coordinated activity of various organs and their systems are carried out, the very existence of the organism is supported.

In changing environmental conditions, the preservation of the vital activity of the organism and adaptive behavior is carried out due to the formation of conditioned reflexes with the obligatory participation of the cerebral cortex. They are not congenital, but are formed during life on the basis of unconditioned reflexes under the influence of certain environmental factors. Conditioned reflexes are strictly individual, i.e., in some individuals of a species, this or that reflex may be present, while in others it may be absent.

unconditioned reflexes. The value of unconditioned reflexes

Maintaining the constancy of the internal environment (homeostasis);
- preservation of the integrity of the body (protection from damaging environmental factors);
- reproduction and conservation of the species as a whole.

Unconditioned reflexes and their significance for the development of the child

Birth is a big shock for the child's body. From a vegetative, vegetative existence in a relatively constant environment (the mother's organism), he suddenly passes into completely new conditions of the air environment with an infinite number of frequently changing stimuli, into the world where he has to become a rational person.

The life of a child in new conditions is provided by innate mechanisms. It is born with a certain willingness of the nervous system to adapt the body to external conditions. So, immediately after birth, reflexes are activated that ensure the work of the main body systems (respiration, blood circulation - approx. site). In the early days, you can also note the following. Strong skin irritation (an injection, for example) causes a protective withdrawal, the flashing of an object in front of the face causes squinting, and a sharp increase in the brightness of light causes pupil constriction, etc. These reactions are protective reflexes.

In addition to protective ones, reactions aimed at contact with an irritant can be detected in newborns. These are orienting reflexes. Observations have established that already in the period from the first to the third day, a strong light source causes the head to turn: in the children's room of the maternity hospital on a sunny day, the heads of most newborns, like sunflowers, are turned towards the light. It has also been proven that already in the first days of the newborn it is common to follow a slowly moving light source. Orientation-food reflexes are also easily evoked. Touching the corners of the lips, cheeks causes a search reaction in a hungry child: he turns his head towards the stimulus, opens his mouth.
In addition to those listed, the child has several more innate reactions: a sucking reflex - the child immediately begins to suck the object put into his mouth; grasping reflex - touching the palm causes a grasping reaction; repulsion (crawling) reflex - when touching the soles of the feet and some other reflexes.

Thus, the child is armed with a certain number of unconditioned reflexes that appear in the very first days after birth. In recent years, scientists have proven that some reflex reactions appear even before birth. So, after eighteen weeks, the fetus develops a sucking reflex.

Most inborn reactions are necessary for a child to live. They help him to adapt to the new conditions of existence. Thanks to these reflexes, a new type of breathing and nutrition becomes possible for the newborn. If before birth the fetus develops at the expense of the mother's body (through the walls of the vessels of the placenta - the child's place - nutrients and oxygen enter the blood of the fetus from the mother's blood), then after birth the child's body switches to pulmonary breathing and the so-called oral nutrition (through the mouth and stomach). -intestinal tract). This adaptation occurs reflexively. After the lungs are filled with air, the whole system of muscles is included in the rhythmic respiratory movements. Breathing is easy and free. Feeding occurs through the sucking reflex. The innate actions included in the sucking reflex are at first poorly coordinated with each other: when sucking, the child chokes, suffocates, his strength quickly runs out. All his activity is directed to sucking for the sake of saturation. The establishment of reflex automatism of thermoregulation is also very important: the child's body is getting better and better adapted to temperature changes.

Formation and biological significance of conditioned reflexes

Conditioned reflexes are formed as a result of a combination of an unconditioned reflex with the action of a conditioned stimulus. For this, two conditions must be met:

1) the action of the conditioned stimulus must necessarily somewhat precede the action of the unconditioned stimulus;

2) the conditioned stimulus must be repeatedly reinforced by the action of the unconditioned stimulus.

The mechanism for the formation of a conditioned reflex consists in establishing a temporary connection (short circuit) between two foci of excitation in the mayor of the brain. For the example considered, such foci are the centers of salivation and hearing.
The arc of the conditioned reflex, in contrast to that of the unconditioned reflex, is much more complicated and includes receptors that perceive conditioned irritation, a sensory nerve that conducts excitation to the brain, a section of the cortex associated with the center of the unconditioned reflex, a motor nerve and a working organ.

Conditioned reflexes in higher animals, and especially in humans, are developed constantly. This phenomenon is explained by the dynamism of the external environment, to the constantly changing conditions of which the nervous system must quickly adapt.
Thus, if unconditioned reflexes give only a strictly limited orientation in the environment, then conditioned reflexes provide a universal orientation.

The biological significance of conditioned reflexes in the life of humans and animals is enormous, since they provide their adaptive behavior - they allow you to accurately navigate in space and time, find food (by sight, smell), avoid danger, eliminate harmful effects for the body. With age, the number of conditioned reflexes increases, the experience of behavior is acquired, thanks to which the adult organism is better adapted to the environment than the child's.



PHYSIOLOGY OF HIGHER NERVOUS ACTIVITY. INTEGRATED ACTIVITY OF THE BRAIN AND SYSTEM ORGANIZATION OF ADAPTIVE BEHAVIORAL REACTIONS. TEACHING I.P. PAVLOVA ON TYPES OF HIGHER NERVOUS ACTIVITY

Higher nervous activity and its age features. Conditioned and unconditioned reflexes.

1. Differences between conditioned reflexes and unconditioned ones:

· Unconditioned reflexes- innate reactions of the body, they were formed and fixed in the process of evolution and are inherited.

· Conditioned reflexes arise, are fixed, fade away during life and are individual.

Unconditioned reflexes necessarily occur if certain receptors are affected by adequate stimuli.

Conditioned reflexes require special conditions for their formation, they can be formed to any stimuli (of optimal strength and duration) from any receptive field.

· Unconditioned reflexes are relatively constant, stable, unchanged and persist throughout life.

Conditioned reflexes are changeable and more mobile.

Unconditioned reflexes can be carried out at the level of the spinal cord and brain stem.

Conditioned reflexes are a function of the cerebral cortex, implemented with the participation of subcortical structures.

Unconditioned reflexes can ensure the existence of the organism only at the earliest stage of life.

The adaptation of the body to constantly changing environmental conditions is provided by conditioned reflexes developed throughout life.

Conditioned reflexes are changeable. In the process of life, some conditioned reflexes, losing their meaning, fade away, others are developed.

The biological significance of unconditioned reflexes.

An organism is born with a certain set of unconditioned reflexes. They provide maintenance of vital activity of an organism in rather constant conditions of existence. These include unconditioned reflexes:

· food- chewing, sucking, swallowing, separation of saliva, gastric juice, etc.,

· defensive- withdrawing the hand from a hot object, coughing, sneezing, blinking when a jet of air enters the eye, etc.,

· sexual reflexes- sexual intercourse, feeding and caring for offspring,

· thermoregulatory,

· respiratory,

· cardiovascular,

· maintaining the constancy of the internal environment of the body(homeostasis), etc.

Biological significance of conditioned reflexes.

The student learns about conditioned and unconditioned reflexes even at the first lessons of zoology, when a vivid example of the “Pavlov’s dog” is given, which begins to salivate after a certain signal is given. Then the student gets the first idea about the role of reflexes in human life and about the existence of the so-called "first signal system". However, outside the school curriculum there is such a thing as a “second signaling system”, which is no less important.

The role of the system of conditioned and unconditioned reflexes in human life

What are the types of reflexes, what is the difference between conditioned reflexes and unconditioned ones, and what is their significance?

For example, you burned your finger with a match and pull your hand away, and immediately, without hesitation. Painful irritation of the skin was transmitted by nerve fibers to a group of cells in the central nervous system that are in charge of the motor functions of the muscles of the hands. The excitement that arose in them was immediately transmitted along other nerve fibers to the muscles. They contracted sharply - the hand twitched, the fire no longer burns the finger. This type of human reflex is called unconditioned, there are many such reflexes and they are all congenital.

And conditional reflexes need to be created, worked out. Research in this area is associated with the name of our famous physiologist IP Pavlov. It was this scientist who substantiated the importance of reflexes in human life and proved that if the system of unconditioned reflexes is repeatedly accompanied by a certain stimulus, then after a while the stimulus will begin to cause this reflex.

Here is an example. You are pricked with a needle and at the same time the bell is rung. After a certain number of repetitions, the sound of the bell becomes a signal to withdraw the hand. The needle did not prick, and the hand twitched involuntarily. The conditioned reflex has been created.

Conditioned and unconditioned human reflexes play an important role in life. The child, having been burned by fire, further withdraws his hand before the fire again scorches his skin. A forest animal, having become intimately acquainted with some kind of danger, behaves more cautiously at another time. IP Pavlov called this perception of the surrounding reality by the human and animal brain the first signal system.

In addition, a person has a second signaling system. In this case, the conditioned stimulus is words-images and concepts. If, say, a person has experienced the strongest fright associated with a fire, then with him it is enough to shout “Fire!” To cause the same fright.

Both signal systems of conditioned reflexes in our body are closely interconnected. They represent the work of our central nervous system. And the latter regulates all the activities of the body. It is known that various emotional experiences (fear, grief, joy, etc.) can cause changes in the work of the heart (acceleration and slowing of the heartbeat, constriction or expansion of blood vessels, redness or blanching of the skin), can lead to gray hair and so on. This means that in one way or another we can influence the work of many internal organs, including the word. It can significantly affect the psyche, and therefore, the work of the whole organism.

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Conditioned and unconditioned reflexes are characteristic of the entire animal world.

In biology, they are considered as the result of a long evolutionary process and represent the response of the central nervous system to external environmental influences.

They provide a very fast response to a particular stimulus, which significantly saves the resources of the nervous system.

Classification of reflexes

In modern science, such reactions are described using several classifications that describe their features in different ways.

So, they are of the following types:

1. Conditional and unconditional - depending on how they are formed.
2. Exteroreceptive (from "extra" - external) - reactions of external receptors of the skin, hearing, smell and vision. Interoreceptive (from "intero" - inside) - reactions of internal organs and systems. Proprioceptive (from "proprio" - special) - reactions associated with the sensation of one's own body in space and formed by the interaction of muscles, tendons and joints. This is a classification by type of receptor.
3. According to the type of effectors (zones of a reflex response to information collected by receptors), there are: motor and vegetative.
4. Classification based on a specific biological role. Allocate species aimed at protection, nutrition, orientation in the environment and reproduction.
5. Monosynaptic and polysynaptic - depending on the complexity of the neural structure.
6. According to the type of influence, excitatory and inhibitory reflexes are distinguished.
7. And according to where the reflex arcs are located, they distinguish cerebral (various parts of the brain are included) and spinal (spinal cord neurons are included).

What is a conditioned reflex

This is a term denoting a reflex formed as a result of the fact that at the same time for a long time a stimulus that does not cause any reaction is presented with the stimulus that causes some specific unconditioned reflex. That is, the reflex response as a result extends to an initially indifferent stimulus.

Where are the centers of conditioned reflexes located?

Since this is a more complex product of the nervous system, the central part of the neural arc of conditioned reflexes is located in the brain, and specifically in the cerebral cortex.

Examples of conditioned reflexes

The most striking and classic example is Pavlov's dog. The dogs were presented with a piece of meat (this caused the secretion of gastric juice and salivation) along with the inclusion of a lamp. As a result, after a while, the process of activating digestion started when the lamp was turned on.

A familiar example from life is the feeling of cheerfulness from the smell of coffee. Caffeine does not yet directly affect the nervous system. He is outside the body - in a circle. But the feeling of cheerfulness is turned on only from the smell.

Many mechanical actions and habits are also examples. They rearranged the furniture in the room, and the hand reaches in the direction where the closet used to be. Or the cat that runs to the bowl when it hears the rustle of the food box.

The difference between unconditioned reflexes and conditioned

They differ in that the unconditional are innate. They are the same for all animals of one species or another, as they are inherited. They are quite invariable throughout the life of a person or animal. From birth and always occur in response to receptor irritation, and are not produced.

Conditionals are acquired during life, with experience in interaction with the environment. Therefore, they are quite individual - depending on the conditions under which it was formed. They are fickle throughout life and can die out if they are not reinforced.

Conditioned and unconditioned reflexes - comparative table

The difference between instincts and unconditioned reflexes

An instinct, like a reflex, is a biologically significant form of animal behavior. Only the second is a simple short response to a stimulus, and instinct is a more complex activity that has a specific biological purpose.

The unconditioned reflex is always triggered. But instinct is only in a state of biological readiness of the body and start this or that behavior. For example, mating behavior in birds only kicks in at certain times of the year, when chick survival can be at its maximum.

What is not characteristic of unconditioned reflexes

In short, they cannot change throughout life. Do not differ in different animals of the same species. They cannot disappear or stop appearing in response to a stimulus.

When conditioned reflexes fade

Extinction occurs as a result of the fact that the stimulus (stimulus) ceases to coincide in time of presentation with the stimulus that caused the reaction. They need reinforcements. Otherwise, without being reinforced, they lose their biological significance and fade away.

Unconditioned reflexes of the brain

These include the following types: blinking, swallowing, vomiting, indicative, balance maintenance associated with hunger and satiety, inhibition of movement in inertia (for example, with a push).

Violation or disappearance of any of these types of reflexes can be a signal of serious disorders in the brain.

Pulling your hand away from a hot object is an example of what kind of reflex

An example of a pain reaction is pulling your hand away from a hot kettle. It's an unconditional view, response of the body to the dangerous effects of the environment.

Blink reflex - conditioned or unconditioned

Blinking reaction is an unconditioned species. It occurs as a result of dryness of the eye and to protect against mechanical damage. All animals and humans have it.

Salivation in a person at the sight of a lemon - what a reflex

This is a conditional view. It is formed because the rich taste of lemon provokes salivation so often and strongly that as a result of simply looking at it (and even remembering it), a response is triggered.

How to develop a conditioned reflex in a person

In humans, unlike animals, a conditional view is developed faster. But for all the mechanism is the same - the joint presentation of incentives. One, causing an unconditioned reflex, and the other - indifferent.

For example, for a teenager who fell off a bicycle to some particular music, later unpleasant feelings arising to the same music may become the acquisition of a conditioned reflex.

What is the role of conditioned reflexes in the life of an animal

They enable an animal with rigid, unchanging unconditional reactions and instincts to adapt to conditions that are constantly changing.

At the level of the whole species, this is an opportunity to live in the largest possible areas with different weather conditions, with different levels of food supply. In general, they make it possible to react flexibly and adapt to the environment.

Conclusion

Unconditioned and conditioned responses are essential to the survival of the animal. But it is in interaction that they allow to adapt, multiply and grow the most healthy offspring.