Reflex is the main form of activity of the nervous system.

The assumption of a fully reflexive nature of the activity of the higher parts of the brain was first developed by the physiologist I.M.Sechenov. Before him, physiologists and neurologists did not dare to raise the question of the possibility of physiological analysis mental processes that were given to solve psychology.

Further, the ideas of I.M.Sechenov were developed in the works of I.P. Pavlov, who opened the way for an objective experimental study of the functions of the cortex, developed a method for the development of conditioned reflexes and created the doctrine of higher nervous activity. Pavlov, in his writings, introduced the division of reflexes into unconditioned, which are carried out by innate, hereditarily fixed nerve pathways, and conditioned, which, according to Pavlov's views, are carried out through nervous connections formed in the process of the individual life of a person or animal.

Charles S. Sherrington (Nobel Prize in Physiology or Medicine, 1932) made a great contribution to the formation of the doctrine of reflexes. He discovered coordination, mutual inhibition and facilitation of reflexes.

The meaning of the doctrine of reflexes

The study of reflexes provided a lot for understanding the very essence of nervous activity. However, the reflex principle itself could not explain many forms of purposeful behavior. At present, the concept of reflex mechanisms is supplemented by the concept of the role of needs in the organization of behavior, it has become a generally accepted idea that the behavior of animals, including humans, is active in nature and is determined not only by certain stimuli, but also by plans and intentions that arise under the influence of certain needs. These new ideas were expressed in the physiological concepts of PK Anokhin's "functional system" or NA Bernstein's "physiological activity". The essence of these concepts boils down to the fact that the brain can not only adequately respond to stimuli, but also foresee the future, actively make plans of behavior and implement them in action. The idea of ​​an "action acceptor" or "model of the required future" allows us to speak of "outstripping reality."

General mechanism of reflex formation

Neurons and pathways for nerve impulses during a reflex act form a so-called reflex arc:

Stimulus - receptor - neuron - effector - reaction.

In humans, most reflexes are carried out with the participation of at least two neurons - sensory and motor (motor neuron, executive neuron). In the reflex arcs of most reflexes, interneurons (interneurons) are also involved - one or more. Any of these neurons in humans can be located both inside the central nervous system (for example, reflexes with the participation of central chemo- and thermoreceptors) and outside it (for example, reflexes of the metasympathetic division of the ANS).

Classification

On a number of grounds, reflexes can be divided into groups.

1. By type of education: conditioned and unconditioned reflexes.
2. By types of receptors: exteroceptive (skin, visual, auditory, olfactory), interoceptive (from receptors of internal organs) and proprioceptive (from receptors of muscles, tendons, joints)
3. By effectors: somatic, or motor (skeletal muscle reflexes), for example, flexor, extensor, locomotor, statokinetic, etc.; vegetative - digestive, cardiovascular, sweating, pupillary, etc.
4. By biological significance: defensive, or protective, digestive, sexual, indicative.
5. According to the degree of complexity of the neural organization of reflex arcs, monosynaptic arcs are distinguished, the arcs of which consist of afferent and efferent neurons (for example, the knee), and polysynaptic, the arches of which also contain one or more intercalary neurons and have two or more synaptic switches (for example, flexor painful).
6. By the nature of the influences on the activity of the effector: excitatory - causing and intensifying (facilitating) its activity, inhibitory - weakening and suppressing it (for example, a reflex increase in the heart rate of the sympathetic nerve and its reduction or cardiac arrest - by a wandering one).
7. According to the anatomical location of the central part of the reflex arcs, spinal reflexes and reflexes of the brain are distinguished. In the implementation of spinal reflexes, neurons located in the spinal cord are involved. An example of the simplest spinal reflex is pulling the hand away from a sharp pin. Reflexes of the brain are carried out with the participation of neurons in the brain. Among them are bulbar, carried out with the participation of neurons of the medulla oblongata; mesencephalic - with the participation of midbrain neurons; cortical - with the participation of neurons in the cerebral cortex. There are also peripheral reflexes carried out by the metasympathetic division of the ANS without the participation of the head and spinal cord.

Unconditional

Unconditioned reflexes are hereditarily transmitted (congenital) reactions of the body inherent in the entire species. They perform a protective function, as well as the function of maintaining homeostasis (constancy of the internal environment of the body).

Unconditioned reflexes are inherited, unchanging reactions of the body to certain influences from the external or internal environment, regardless of the conditions for the occurrence and course of reactions. Unconditioned reflexes ensure the adaptation of the body to constant environmental conditions. The main types of unconditioned reflexes: food, protective, orienting, sexual.

An example of a protective reflex is the reflexive withdrawal of the hand from a hot object. Homeostasis is maintained, for example, by a reflexive increase in respiration with an excess of carbon dioxide in the blood. Almost every part of the body and every organ is involved in reflex reactions.

Neural organization of the simplest reflex

The simplest vertebrate reflex is considered to be monosynaptic. If the arc of the spinal reflex is formed by two neurons, then the first of them is represented by a cell of the spinal ganglion, and the second is a motor cell (motoneuron) of the anterior horn of the spinal cord. A long dendrite of the spinal ganglion goes to the periphery, forming a sensitive fiber of a nerve trunk, and ends with a receptor. The axon of the neuron of the spinal ganglion is part of the posterior root of the spinal cord, reaches the motor neuron of the anterior horn and through the synapse connects to the body of the neuron or one of its dendrites. The axon of the motor neuron of the anterior horn is part of the anterior root, then the corresponding motor nerve and ends with a motor plaque in the muscle.

There are no pure monosynaptic reflexes. Even the knee reflex, which is a classic example of a monosynaptic reflex, is polysynaptic, since the sensory neuron not only switches to the extensor motor neuron, but also gives off the axonal collateral, which switches to the insertion inhibitory neuron of the antagonist muscle, the flexor.

Conditional

Conditioned reflexes arise in the course of individual development and the accumulation of new skills. The development of new temporary connections between neurons depends on the conditions of the external environment. Conditioned reflexes are formed on the basis of unconditioned ones with the participation of the higher parts of the brain.

The development of the doctrine of conditioned reflexes is associated primarily with the name of I.P. Pavlov. He showed that a new stimulus can start a reflex response if it is presented for some time together with an unconditioned stimulus. For example, if a dog is allowed to sniff meat, then gastric juice is secreted from it (this is an unconditioned reflex). If, however, the bell rings with meat, the dog's nervous system associates this sound with food, and gastric juice will be secreted in response to the bell, even if meat is not presented. Conditioned reflexes are at the core of acquired behavior... These are the simplest programs. The world around us is constantly changing, so only those who quickly and expediently respond to these changes can successfully live in it. With the acquisition of life experience in the cerebral cortex, a system of conditioned reflex connections develops. This system is called dynamic stereotype... It underlies many habits and skills. For example, having learned to skate, bike, we subsequently no longer think about how to move in order not to fall.

Axon reflex

The axon reflex is carried out along the branches of the axon without the participation of the neuron body. The reflex arc of the axon reflex does not contain synapses and neuronal bodies. With the help of axon reflexes, the regulation of the activity of internal organs and blood vessels can be carried out (relatively) independently of the central nervous system.

Pathological reflexes

Pathological reflexes is a neurological term for reflex reactions that are unusual for a healthy adult. In some cases, they are characteristic of earlier stages of phylo- or ontogenesis.

There is an opinion that mental dependence on something is caused by the formation of a conditioned reflex. For example, mental dependence on drugs is associated with the fact that the intake of a certain substance is associated with a pleasant state (a conditioned reflex is formed, which persists for almost the entire life).

Harlampy Tiras, PhD in Biology, believes that "the idea of ​​conditioned reflexes that Pavlov worked with is entirely based on forced behavior, and this gives an incorrect registration [of experimental results]." “We insist: the object should be studied when it is ready for it. Then we act as observers without raping the animal, and, accordingly, we get more objective results. " The author does not specify what exactly the author means by “violence” of an animal and what are the “more objective” results.

For many centuries, people have pondered the amazing adaptability of animal behavior to habitat conditions. The purposeful, rational behavior of a person seemed even more mysterious. The explanation for this was first expressed in 1863 by the great Russian physiologist I. M. Sechenov, who explained the behavior and "mental" - mental activity the principle of the work of the nervous system.

I.P. Pavlov experimentally confirmed, creatively expanded and developed I.M.Sechenov's position on the reflex principle of brain activity and created a new section in science - physiology of higher nervous activity of animals and humans... Under lower nervous activity I.P. Pavlov meant the reflex regulation of the physiological functions of the body, higher nervous activity defined as a mental activity that determines the reflex regulation of a person's relationship with the environment.

Higher nervous activity provides individual behavioral adaptation of man and higher animals to changing conditions of the environment and internal environment, is reflex in nature, is carried out by unconditioned and conditioned reflexes.

Unconditioned reflexes

Unconditioned reflexes- ensure the maintenance of life in relatively constant environmental conditions, they are inherent in humans from birth. For example, the separation of saliva under the direct action of food on the mucous membrane of the mouth: food acts on the sensitive nerve endings of the oral cavity and causes excitement in them, which rushes along the centripetal nerves to the salivary gland and activates it. This reflex, like all unconditioned reflexes, has a certain reflex arc, ready for the moment of birth. Unconditioned reflexes are congenital, hereditary, specific and always arise under constant conditions (necessarily, of course) and persist throughout the life of the organism.

Unconditioned reflexes include food, defensive, sexual and orientation reflexes, due to which the integrity of the body is maintained, the constancy of the internal environment is maintained and reproduction occurs. From the Animals section, you know the instinctive behavior of many animals. These are also unconditioned reflexes. Instincts are a system of innate unconditioned reflex behavioral reactions associated with the continuation and preservation of the species.

Conditioned reflexes

In an infinitely complex and changeable environment, adaptability with the help of unconditioned reflexes is insufficient and the body can die if it does not prepare in advance for new changes in the environment. Thus, an animal has incomparably more chances to save itself if it detects signs of a predator approaching in advance. Consequently, everything that signals, warns of the approach of a predator - noise, smell, sight, etc., acquires vitality for the animal. essential and evokes appropriate reactions in him, in accordance with the prevailing conditions environment.

Similarly, the sight, the smell of familiar food, everything that signals, warns a hungry person about the possibility of a quick meal, makes him saliva a separating reflex, preliminary secretion of digestive juices, which allows you to quickly and fully process food when it enters the digestive system.

These are reflexes that allow you to adapt to a future event that has not yet occurred. I.P. Pavlov named conditioned reflexes, because they are formed under certain conditions: it is necessary to repeatedly coincide in time with the action of two stimuli - the future signal, or conditioned, and unconditioned, that is, causing an unconditioned reflex. The conditioned stimulus should somewhat precede the unconditioned stimulus, as it signals about it. Thus, a conditioned reflex is a reflex acquired by the body during life and formed as a result of a combination of conditioned stimuli with an unconditioned one. In mammals, animals and humans, the arcs of conditioned reflexes pass through the cerebral cortex.

Pavlov also called the conditioned reflex a temporary connection, because this reflex manifests itself only during the time when the conditions under which it was formed are in effect; acquired by the individual, since it is formed in the individual life of the organism. Conditioned reflexes can be formed by any stimulus on the basis of any unconditioned reflex.

Conditioned reflexes form the basis of skills, habits, training and education, the development of speech and thinking in a child, labor, social and creative activities.

Studies have established that the basis for the formation of conditioned reflexes is the establishment of temporary connections in the cerebral cortex between the nerve centers of the unconditioned reflex and the conditioned stimulus.

Excitation and inhibition

Along with excitation in the cerebral cortex, an inhibition of the active state occurs, a delay in some reactions, which makes it possible to implement others. With the help of the formation of conditioned reflexes and their inhibition, a deeper adaptation of the organism to specific conditions of existence is carried out.

Excitation and inhibition are two interrelated processes that continuously occur in the cerebral cortex and determine its activity. IP Pavlov divided the phenomenon of inhibition in the cerebral cortex into 2 types: external and internal.

External braking occurs due to the appearance in the cerebral cortex of another focus of excitation. It is caused by an additional stimulus, the action of which causes another reflex act.

Internal braking occurs as a result of reinforcement of the conditioned stimulus by the unconditioned one, which leads to the gradual disappearance of the conditioned reflex. It got the name extinction of the conditioned reflex... Internal inhibition is characteristic only of the higher parts of the central nervous system and is very important for the body.

Reflex activity provides a connection between the body and the environment, allows you to adequately respond to external and internal changes and quickly protect yourself from external harmful influences and respond to internal changes. To eat is to find prey. Maintain the constancy of the parameters of the internal environment, adjust these parameters.

Reflex arc and reflex act.

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

The reflex arc consists of the following elements:

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

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

3. Insertion / associative / interneurons- located in the central nervous system, receive information from a sensory neuron and transmit it to an efferent neuron - a motor neuron / executive

4. Efferent neuron / motor neuron- receives information from the interneuron and transfers it to the effector / executive organ. The bodies of motor neurons are in the central nervous system, and the axons belong to the peripheral NS

5. Working organ / effector- muscles and glands. Therefore, all reflex responses can be reduced either to the reduction of m-ts, or to the allocation of a secret.

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

Reflex time- the time from the moment the stimulus acts on sensitive receptors to the response from the effector.

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

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

2. Monosynaptic composition of 1 synapse, when inf from feeling is transmitted to the motor. In humans, only tendon reflexes are monosynaptic - the knee, plantar, and Achilles reflexes.

Reflex is a complex nervous process, 4 functional links:

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

2- Deployment of the nervous process in the central nervous system, that is, in structures that are called nerve centers and central parts of the analyzers.

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

Any reflex act should be assessed depending on the achievement of the desired result (Are the muscles contracted enough to ensure flexion of the arm with the elbow joint?) Such an assessment is carried out on the basis of feedback: the effector contains sensitive receptors, the information from which enters the central nervous system (in the skeletal muscles, these are proprioceptors)

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

If the result of the reflex of the district is not reached, the switching excitation to new afferent pathways.

Therefore, the number of afferent and efferent neurons correlates as 5 to 1. That is, the same reflex response can be observed to a variety of stimuli. Can be used 1 and the same final path. Ie motoneurons of certain group m-c, and the afferent links of these reflexes are different.

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

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

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Spinal Cord Physiology

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Date the page was created: 2016-02-12

CONDITIONAL REFLECTIVE ACTIVITIES OF THE BODY

Reflex. Reflex arc. Types of reflexes

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

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

An example of a simple reflex arc is a tendon reflex arc, such as a knee reflex arc.

The reflex arcs of most reflexes include not two, but large quantity neurons: receptor, one or more intercalated and effector. Such reflex arcs are called complex, multi-neuronal.

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

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

2) depending on the type of irritated receptors:

exteroceptive, interoceptive and proprioceptive;

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

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

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

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

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

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

1) unilateral conduct of excitation;

2) delay in conducting excitation;

3) summation of excitations;

4) transformation of the rhythm of excitement;

5) reflex aftereffect;

6) fast fatigability.

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

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

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

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

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

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

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

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

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

Reflex tone of the nerve centers. In a state of relative rest, without causing additional irritation, discharges of nerve impulses come from the nerve centers to the periphery to the corresponding organs and tissues. At rest, the frequency of discharges and the number of simultaneously operating neurons are very small. Rare impulses continuously coming from nerve centers cause tone (moderate tension) of skeletal muscles, intestinal smooth muscles and blood vessels. This constant excitement of the nerve centers is called the tone of the nerve centers. It is supported by afferent impulses continuously coming from receptors (especially proprioceptors) and various humoral influences (hormones, COs, etc.).

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

In 1862, classical experiments were carried out by the founder of Russian physiology, I. M. Sechenov, which received the name "central inhibition". On the frog's visual hillocks, separated from the cerebral hemispheres, I.M.Sechenov placed a crystal of sodium chloride (table salt) and observed the inhibition of spinal reflexes. After elimination of the stimulus, the reflex activity of the spinal cord was restored.

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

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

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

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

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

No special braking structures are required for secondary braking to occur. It develops as a result of changes in the functional activity of ordinary excitable neurons.

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

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

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

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

The principles of coordination in the activity of the central nervous system

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

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

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

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

The principle of reciprocity(conjugation). This phenomenon was studied by I.M.Sechenov, N.E. Vvedensky, Sherrington. Its essence lies in the fact that when some nerve centers are excited, the activity of others can be inhibited. The principle of reciprocity has been shown in relation to the nerve centers of the antagonists of the flexor and extensor muscles of the limbs. It is most clearly manifested in animals with a removed brain and preserved spinal cord (spinal animal). The described phenomena are associated with the fact that when the center of flexion of one limb is excited, reciprocal inhibition of the center of extension of the same limb occurs. On the symmetrical side, there is an inverse relationship: the center of the extensors is excited and the center of the flexors is inhibited. Walking is possible only with such interconnected (reciprocal) innervation.

Reciprocal relationships between the centers of the brain determine a person's ability to master complex labor processes and no less complex special movements performed during swimming, acrobatic exercises and so on.

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

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

Feedbacks can be positive and negative. Positive feedbacks enhance reflex reactions, negative ones suppress them.

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

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

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

Dominants can be of exogenous and endogenous origin. An exogenous dominant arises under the influence of environmental factors. For example, when reading an interesting book, a person may not hear the music sounding on the radio at that time.

The endogenous dominant arises under the influence of factors of the internal environment of the body, mainly the images of hormones and other physiologically active substances. For example, with a decrease in the content of nutrients in the blood, especially glucose, the food center is excited, which is one of the reasons for the food setting of the body of animals and humans.

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

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

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

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

The analysis of stimuli is performed by complex nerve analyzer organs. Each analyzer consists of three parts: 1) peripheral perceiving organ (receptor); 2) conductive afferent, those. centripetal path through which nervous excitement is transmitted from the periphery to the center; 3) the cortical part of the analyzer (central link).

Transmission of nervous excitement from receptors, first to the central parts of the nervous system, and then from them along efferent, those. centrifugal, pathways back to the receptors for the response that occurs during the reflex is carried out along the reflex arc. Reflex arc (reflex ring) consists of a receptor, an afferent nerve, a central link, an efferent nerve and an effector (muscle or gland).

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

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

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

Unconditioned reflexes. Instincts

Unconditioned reflexes have been allocated to a special category to designate the specific reactions of the body to internal and external stimuli, which are carried out on the basis of innate neural connections, i.e. reflecting the phylogenetic experience of adaptation to the conditions of existence. Unconditioned reflexes are relatively constant, manifest themselves stereotypically in response to adequate stimulation of a certain receptive field and serve as the basis for the formation of numerous conditioned reflexes associated with individual experience. Unconditioned reflexes provide coordinated activity aimed at maintaining the constancy of many parameters of the internal environment, the interaction of the body with the external environment, coordinated activity of somatic, visceral and autonomic reactions.

However, optimal adaptation to the changing states of the external and internal environments of the body is achieved with the help of conditioned reflexes, due to which stimuli that are indifferent to certain activities acquire the quality of biologically significant signals.

Features of unconditioned reflexes

Several classifications of unconditioned reflexes in accordance with the nature of the stimuli that cause them, their biological role, levels of control (communication with certain parts of the central nervous system), the order of sequence in a specific adaptive act. The authors of these classifications reflected in them their scientific interests and methodological guidelines. I.P. Pavlov described food, defensive, orientation, parental and child reactions, subdivided into more fractional reflexes. Thus, food reflexes associated with the activity of the food center include the search, extraction, capture, taste testing of food, the secretion of saliva and digestive juices in the gastrointestinal tract, and its motor activity.

In the works of I.P. Pavlova, there are also indications of the following unconditioned reflexes: food (positive and negative), indicative, collecting, goals, caution, freedom, exploratory, self-preserving (positive and negative), aggressive, watchdog, submission, sexual (male and female), play, parental, nesting, migratory, social, drinking.

ON. Rozhansky identified 24 reflexes included in the following six groups: general activity, metabolic, inter-animal relations, continuation of the species and reproduction, ecological and non-behavioral reflexes of the subcortical-stem parts of the brain. This classification almost does not affect the autonomic sphere of regulation, which plays a large role in the implementation of behavioral acts.

A broader classification is based on the study of the adaptive aspects of unconditioned reflex activity. The representative of the ecological and physiological direction A.D. Slonim proposed to divide unconditioned reflexes into three groups of reactions, associated with maintaining the constancy of the internal environment, changes in the external environment and preservation of the species.

These classifications provide not only a description of behavior, but also an elucidation of the underlying physiological mechanisms. The latter is of lesser interest to ethologists who also study behavior in an environment adequate for an animal. Here's an example classification types of behavior, proposed by the German ethologist G. Tembrok.

Metabolic behavior consisting of food and food intake, urination and defecation, food storage, rest and sleep, and stretching.

Comfortable behavior.

Defensive behavior.

Breeding behavior, consisting of area guarding, mating, offspring care.

Social (group) behavior.

Construction of nests, burrows and shelters.

Although, in many respects, such a division is close to the above classifications of the physiologists N.A. Rozhansky and A.D. Slonima, it gravitates more towards external description innate stereotypes of behavior.

For P.V. Simonov, the classifying principle of grouping the most complex unconditioned reflexes was the ideas of V.I. Vernadsky and A.A. Ukhtomsky about assimilation by living beings of different levels of organization in the geo-, bio-, and for humans also in the socio- and noosphere (intellectual exploration of the world). P.V. Simonov identified the following unconditioned reflexes: vital, role (zoosocial) and self-development. Vital unconditioned reflexes include food, drinking, sleep regulation, defensive reflexes (including the "biological caution" reflex), the energy-saving reflex, and many others. They do not require the participation of another individual, and the impossibility of their implementation leads to physical death. Role (zoosocial) unconditioned reflexes, on the contrary, are manifested in the process of interaction with other individuals of this species. Unconditioned self-development reflexes reflect exploratory behavior, reflexes of freedom, imitation and play.

Polish neurophysiologist J. Konorski divided unconditioned reflexes into according to their biological role in conservation associated with entering the body and removing everything necessary from it; restorative (sleep) aimed at preserving the species (copulation, pregnancy, caring for offspring), and protective ensuring the removal of the whole body or its individual parts from the sphere of action of a harmful or dangerous stimulus for the body (withdrawal and retreat reflexes) or associated with the elimination of harmful agents that have fallen on the surface of the body or inside the body, destruction or neutralization of harmful agents (offensive reflexes).

Conservation reflexes of attraction are directed directly to the object (food, sexual partner), protective ones are directed in the direction opposite to the harmful stimulus. In the order of the sequence of phases, this classification is supplemented by an indication of preparatory (drive, motivational) and executive (consumative) unconditioned reflexes associated with final actions.

So, based on this classification, we can distinguish preparatory food unconditioned reflexes underlying the formation of states of hunger and satiety. These include reactions that occur when the chemical composition of the blood changes, changes in metabolism, increases or decreases in interoceptive signaling (mainly from receptors in the stomach, intestines and liver).

The initiation and termination of alimentary excitement are determined by nerve and humoral signals perceived by specialized receptors in the hypothalamic region. Many other brain structures are also involved in the formation of states of hunger and satiety. Nutritional impulse depends on internal stimuli and on stimuli emanating from the external environment. Against the background of the dominant motivation of hunger, motor restlessness arises and some sensory systems(in particular, taste and smell). After food enters oral cavity preparatory reflexes are inhibited and executive food reflexes begin to be realized: chewing food, salivation, swallowing a formed food lump, coordinated contractions of the esophagus and stomach, secretion of gastric and pancreatic juices, changes in metabolic reactions, etc.

Equally complex are preparatory and executive unconditioned reflexes associated with sexual or defensive behavior. At the same time, it should be borne in mind that in the process of ontogenesis, preparatory and executive unconditioned reflexes are modified under the influence of external and internal stimuli, therefore, in coordinated adaptive activity, the primary role begins to play conditioned reflexes.

As you can see, reflex control of body functions is carried out by mechanisms of varying complexity. This allowed I.P. Pavlova to divide unconditioned reflexes according to the anatomical principle: simple(spinal), complicated(medulla), complex(midbrain) and the most difficult(the nearest subcortex and cerebral cortex). At the same time I.P. Pavlov pointed to the systemic nature of the regulation of physiological processes, which he considered using the example of the organization of the "food center" - a functional set of structures located at different levels of the brain.

Regulation on consistency as the basic principle of the brain was formulated by A.A. Ukhtomsky in his doctrine of the dominant - the functional association of various nerve centers on the basis of increased excitability. These ideas were developed by P.K. Anokhin, according to which functional systems dynamically combine nerve elements of different levels of the central nervous system, providing certain adaptive effects.

Thus, it is possible to classify unconditional reflex and conditioned reflex activity on the basis of anatomical and functional approaches, between which there are no fundamental contradictions. In recent decades, with the help of stereotaxic technique, it has been possible to determine the participation in specialized unconditioned reflex activity of many parts of the brain (hypothalamus, amygdala, hippocampus, striopallidal system, etc.). The data obtained expanded the understanding of the organization of various forms of behavior.

The development of the theory of automatic regulation has led to the need to consider the organization of innate and acquired behavior in terms of ideas about informational and control activity of the brain... It was allocated six levels its organization (AB Kogan and others): elementary, coordination, integrative, complex unconditioned reflexes, elementary conditioned reflexes and complex forms of higher nervous (mental) activity.

Elementary unconditioned reflexes- simple responses of local importance, implemented in accordance with the rigidly determined program of their segmental centers. They are carried out along one main channel (centripetal, central and centrifugal links). The role of feedback (mostly negative) in the correction of elementary unconditioned reflexes is small. Examples of such a reflex are pulling a burned leg away from the fire or blinking when a speck enters the eye.

Coordination unconditioned reflexes are also carried out at the segmental level, but unlike elementary reflexes, they include a number of cycles, although stereotyped, but admitting correction based on negative and positive feedbacks. An example of a simple coordination reflex is the antagonistic reflex, which matches the contractions of the flexor and extensor muscles.

Integrative unconditioned reflexes- synthesis of coordinated motor acts with their vegetative support into complex reactions of a certain biological value. They maintain homeostasis and correct elementary and coordination reflexes. The implementation of integrative reflexes is determined by suprasegmental mechanisms (mainly by the lower parts of the trunk, structures of the medulla oblongata, midbrain and diencephalon, cerebellum). If for the implementation of elementary and coordination reflexes are mainly important physical properties and local application of the stimulus, then integrative reflexes provide integral responses of the organism (the simplest behavioral acts with their vegetative components).

The mechanisms of nervous regulation of different levels are closely intertwined, so their division is conditional. Even in a spinal animal, several reflex arcs are involved in the implementation of an elementary reflex. Even I.M. Sechenov found that in the frog, the ineffectiveness of removing the damaging stimulus with the paw leads to the involvement of new motor coordination in the reaction. The motor response is determined by the initial state of the reflex apparatus. In a decapitated frog, irritation of the skin of the foot causes its flexion, and with a bent one, extension. The non-stencil of the implementation of congenital reflex programs, manifested even after the removal of the suprasegmental parts of the central nervous system, is much more pronounced in the absence of a violation of its integrity.

Difficulty organizing congenital reactions can be traced on the example of the unconditioned salivary reflex, which was considered to be relatively simple. In reality, it is associated with various receptors (taste, tactile, pain), fibers of several nerves (trigeminal, facial, glossopharyngeal, vagus), many parts of the central nervous system (medulla oblongata, hypothalamus, amygdala, cerebral cortex). Salivation is associated with eating behavior, cardiovascular, respiratory, endocrine, thermoregulatory functions.

Undoubtedly, the reflex secretion of saliva depends not only on the adequate stimulus that causes it, but also on many external and internal factors. An increase in ambient temperature leads to the release of a large amount of "thermoregulatory" saliva with a low organic matter content. The amount of saliva depends on the level of food arousal, the availability of water, the content of table salt in food, hormonal background and many other factors.

Thus, it would seem that relatively simple innate reactions actually enter the system integration of complex mechanisms that determine the maintenance of homeostasis and the relationship of the organism with the external environment. Such integration is extremely plastic, and in accordance with the principle of dominant, the same reactions can enter into complexes associated with the satisfaction of various needs of the body. For example, the salivary reflex can be associated with thermoregulation, eating or defensive behavior.

In the implementation of integrative unconditioned reflexes, which are complexes of coordinated movements with their autonomic support, suprasegmental mechanisms play a leading role. A complex system feedbacks carry out the correction of elementary, coordination and integrative reactions, combined into a single system. It is inseparable from the central mechanisms of instinctive reactions associated with the subcortical-brainstem parts of the brain. The cerebral cortex also plays a certain role in the realization of instinctive reactions.

It can be noted that the division of the levels of unconditional reflex activity, proposed by different authors, is relative. The schematic nature of any of its classification can be traced on the example of one of the fundamental unconditioned reflexes - indicative. It includes three groups of phenomena (L.G. Voronin). Its first form, designated I.P. Pavlov as a reflex "what is it?", Includes many elementary and coordinated reactions - dilation of the pupil, lowering the thresholds of sensitivity to a range of sensory stimuli, contraction and relaxation of the muscles of the eye and ear, turning the head and body towards the source of irritation, sniffing at it, changing the electrical activity of the brain (depression, blockade of the alpha rhythm and the occurrence of more frequent fluctuations), the appearance of a galvanic skin reaction, deepening of breathing, expansion of the blood vessels of the head and narrowing of the vessels of the extremities, an initial slowdown and subsequent increase in heart rate and whole line other changes in the vegetative sphere of the body.

Second form the orienting reflex is associated with specialized search movements and depends on the motivational-need characteristics, i.e. prevailing dominant, and from external stimuli.

Third form an orientation reflex manifests itself in the form of an exploratory reaction, not necessarily associated with satisfaction current needs organism, i.e. based on "curiosity".

In foreign literature, to describe the orienting reflex, they use psychological concepts - attention, setting in conditions of expectation of a stimulus, reaction of surprise, alertness, fear, anxiety, vigilance. From the point of view of a neurophysiologist, the orienting reflex is multicomponent nonspecific reaction organism to "novelty", aimed at increasing the ability of analyzers to differentiate a new phenomenon. It is characterized by the fading effect and independence from the modality and direction of changes in the stimulus O.A. Kostandov).

The exploratory reflex is part of exploratory behavior, which, being congenital, is nevertheless practically inseparable from conditioned reflex activity. This also applies to many other forms of behavior. Therefore, one of the most difficult questions of the physiology of behavior is separation of congenital and acquired reactions.

In an adult individual, congenital activity usually does not manifest itself in its pure form, it is modified by conditioned reflexes that are formed in the process of ontogenesis. Thus, unconditioned reflexes are modified in accordance with the individual adaptation to the peculiarities of existence. Even at the earliest stages of postnatal life, and for some aspects of life in the prenatal period, congenital reactions "overgrow" with conditioned reflex elements. In this case, genetically determined positive reactions can be transformed into negative ones. So, at the earliest stages of life, the preferred sweet taste can become rejected if it is at least once combined with a painful state of the body (discomfort).

Another difficulty in differentiating congenital and acquired reactions is associated with improvement of unconditional reflex activity in the process of individual development. In addition, when interacting with conditioned reflexes, unconditioned ones “mature” in the process of postnatal life (L.A. Orbeli).

Modification of congenital forms of behavior in the process of individual development may depend not only on learning, but also on many indirect influences, ultimately affecting the unconditioned reflex activity. In some cases, it is determined by the ambient temperature at which the body develops, nutritional conditions, and stress.

It is customary to consider behavior as innate if it is impossible to detect the influences of learning or other factors on it in ontogenesis. They try to reveal these influences through experiments using certain types deprivation(e.g. isolation from peers, growing up in the dark, etc.). This method is not always effective, since deprivation, firstly, cannot exclude all environmental influences, and secondly, it causes a number of general changes in the state of the organism. In particular, depending on the stimuli affecting the developing organism (enriched and depleted environment), DNA synthesis in neurons, neurotransmitter balance, and many other components, on which the implementation of behavioral acts depends, are regulated.

The organism's responses are not the result of straightforward developmental processes leading from a gene directly to the behavior of an adult animal and only in some cases altered by external influences. In reality, there is a complex interweaving of causal relationships, when each part of the body can interact with its other parts and the external environment (R. Hind).

The range of variability of the most complex unconditioned reflexes, depending on the conditions of existence at an early age, is not the same for different types activities. Some congenital complexes of movements are extremely stable and cannot be changed by environmental influences, others are more flexible. Fixed sequences of movements that are independent of training are described. They are well traced in insects and birds. So, burrowing wasps of the same species build nests with the help of stereotypical movements, stereotyped movements of domestic roosters when courting chickens.

Fixed complexes of movements are also characteristic of highly developed animals, including humans. Scanning movements of the infant's head are characteristic, making it easier to find the nipple. Other complexes of movements associated with sucking are stereotypically manifested. These reflexes mature even in the prenatal period of development, which was established in observations of premature babies. The grasping reflex, facial expressions of the child and many other manifestations of innate activity do not depend on learning. Observations of representatives of many animal species show that an adequate choice of food can be made without the help of parents, i.e. does not always require prior training. A negative reaction to altitude is manifested in monkeys that have never met with it.

At the same time, many of the most complex unconditioned reflexes are modified in the process of development or require a period of learning for their manifestation. In chicks, the formation of singing is determined not only by innate characteristics, but also by the conditions of feeding by birds of their own or another species (A.N. Promptov). Isolation from peers of rats or puppies leads to irreversible changes in subsequent "social" communication. Isolation of monkeys dramatically disrupts their subsequent sexual and maternal behavior.

Difficulties arising in the separation of genetically determined and developed in the process of life behavioral acts are aggravated by the fact that some congenital forms of behavior appear at relatively late stages of development, when the animal has some experience and conditioned reflex stereotypes have already been formed.

This happens, in particular, with sexual behavior, the readiness for the manifestation of which occurs at a certain age against the background of hormonal changes. However, the effectiveness of mating in many species is also determined by the individual experience acquired before reaching puberty as a result of communication with peers. For example, in adult male cichlid fish reared in isolation, courtship behavior is directed not only to females, but also to males. Similar changes were observed in birds, rodents, and monkeys. Communication with congeners affects sexual behavior in different ways, changing the readiness for mating, reactivity to appropriate stimuli, accuracy of movements and various reactions directly or indirectly associated with reproduction. It should be borne in mind that specific (in this example, sexual) behavior can be modified in adults on the basis of non-specific behavior in relation to it, which manifests itself at earlier stages of ontogenesis.

Hormonal changes during puberty, they can also change the nature of the response to various biologically significant stimuli, which, in turn, affects the implementation of previously developed conditioned reflexes. This pattern is traced on the example of conditioned reflex flavor aversions- negative attitude to congenitally indifferent or preferred gustatory stimuli, combined with a painful condition. Aversion to sweet taste, combined with poisoning once, is equally pronounced in immature rat pups of both sexes. As puberty progresses in females, the motivation to consume substances of a sweet taste associated with an increase in estrogen levels increases and, accordingly, the aversion developed for them decreases. In males, however, their rejection continues to be significant, since androgens do not change this motivation.

Maturation of the central nervous system in the process of ontogenesis and accompanying changes in the balance of biologically active substances in the internal environment of the body are extremely important for the manifestation of various congenital forms of behavior and the conditioned reflex activity developed on their basis. Certain stages of postnatal life have their own characteristics of interaction between unconditional and conditioned reflex activity.

For example, during the first three years of life, puppies develop a conditioned food-procuring reflex to natural or ecologically inadequate odor stimuli when combined with feeding once. From the 4th to the 10th day of life, the ability to develop this reflex disappears and reappears on the 11–12th day, and starting from this period, learning already requires a multiple combination of conditioned and unconditioned stimuli.

Many reactions are formed in the first hours or days of life in birds and mammals with a single combination of stimulation of various sense organs with innate elements of behavior - following a receding object and other purposeful motor acts. This form of study, called imprinting, is formed over a sensitive period lasting from 6-8 hours to 4-5 days. Natural conditioned reflexes, which are also formed very quickly at a certain stage of ontogenetic development and fade out extremely slowly, are close to imprinting.

Complex forms of behavior observed immediately after the transition to postnatal life, which allows them to be attributed to congenital reactions. The process of their ripening cannot be traced "in its pure form", since they are modified due to external influences. The existence of the phenomena of imprinting and natural conditioned reflexes makes it difficult to differentiate between congenital and acquired behavioral acts in postnatal ontogenesis.

There is reason to believe that the implementation of some innate reactions is associated with stimuli that the body is exposed to in prenatal life. Thus, in puppies, the preference for the mother's smell is formed at the end of the antenatal period.

Some congenital reactions do not appear immediately after birth, but at one of the subsequent stages of development. If at this time the animal does not encounter a specific stimulus, then the ability to respond to it without special training does not manifest itself. In this case, errors are possible in classifying some reactions as congenital or developed. For example, for a long time it was believed that dogs raised from the period of transition to the definitive diet on a bread-and-milk diet did not respond with an innate positive reaction to the smell of meat. The first experiments on these animals were carried out only at the age of 7 months. It turned out, however, that on the 16-21st day of the puppy's life, this ability manifests itself. If there is no adequate stimulus, it gradually inhibited and is absent in older puppies who first encounter the smell of meat.

The manifestation of some complex shapes behavior, although determined by the genetic program, can be modulated within certain limits external factors... So, lowering the temperature of the external environment significantly reduces the level play activities the young of some mammals, although it causes a specific irritant - contact with peers.

Many examples can be cited confirming the role of environmental factors in the modification of congenital forms of behavior. but it would be a mistake to contrast the significance of genetic and environmental factors in the development of behavior. All forms of interaction of the organism with the environment, including behavioral ones, are determined by the genetic program and, to one degree or another, are subject to external influences. The genetic program also determines the range of these influences, i.e. so called reaction rate... For some characters, it is strictly fixed, which well illustrates the lack of plasticity in the implementation of certain functions in insects (flight, emergence from the larva or cocoon, sexual behavior).

There are strictly programmed instinctive actions. For example, a female spider, while building a cocoon, produces complexes of stereotyped movements, even if the spider's thread is not produced. She then lays eggs in a non-existent hole, which fall to the ground, and continues an activity that simulates the construction of a cocoon, which in fact does not exist. In this case, the reaction rate is extremely narrow, and instinctive actions do not depend on signals about their effectiveness. For a number of other characters, it is much wider, and the adaptive variability of instinctive actions was also found in insects, which manifests itself, in particular, during the restoration of destroyed dwellings in conditions different from natural ones.

Genetic conditioning of behavior is manifested during the gradual formation of certain behavioral acts in the process of early ontogenesis. The ratio of congenital and acquired components in the reaction of an attack on a prey in kittens has been studied in detail. Initially, only instinctive motor stereotypes are manifested, gradually in the process of training, taking place in conditions of contact with the mother and peers, they are refined and enriched by the movements formed in the learning process.

The initial use of congenital complexes of movements associated with feeding activity was described in puppies during the first days of life during the development of intracerebral self-stimulation of the "reward zones" (positive emotiogenic system). Gradually, the repertoire of movements is enriched with less stereotyped, developed complexes, and they coexist with innate stereotypes of motor activity. Obviously, the instinctive commandment acts on the basis of which the new system purposeful activity are not necessarily eliminated during its formation.

The question of the indispensable reflex basis of each behavioral act is difficult.

The idea of ​​its obligation led I.P. Pavlova to the identification of concepts complex unconditioned reactions and instincts. In many cases, it was possible to find external and internal stimuli that are the impetus for the deployment of a chain of template reactions, but it is not always possible to identify them, which suggests that a number of forms of instinctive activity are manifested spontaneously. Endogenous processes in the central nervous system determine the execution of a number of instinctive acts without visible fluctuations in the state of the external and internal environment. An important role in this is played by circadian and other rhythms that are not defined physiological state organism and various stimuli, although they can shift under their influence.

Autonomous oscillatory processes in various structures of the brain are described, which determine periodic changes in the behavior of animals isolated from relatives and deprived of sight and hearing. Many genetically encoded reactions are determined by changes in the internal environment of the body. So, in deaf from birth Siamese mutant cats, the excitement associated with the cycle of sexual activity is manifested both in behavioral acts (lordosis, etc.) and in specific sound signals. Certain signals are emitted by these animals in a state of hunger and during defensive behavior.

Some norms of reactions in the absence of feedback are suppressed. So, deaf and blind people lack some expressive movements (including sound ones) associated, respectively, with auditory or visual perception. Those born blind smile less over the years than those who are sighted or blind at a later age. However, a number of expressive movements are manifested regardless of the usefulness of sensory systems. An analysis of the expressive movements of children born blind and deaf, recorded on film, showed that the motor skills of laughter in them are exactly the same as in healthy ones (I. Aibl-Eibesfeldt).

The complexes of instinctive movements are usually closely associated with signals from the external and internal environments of the body, although they can be determined by autonomous processes in the central nervous system. However, it is far from always possible to identify them.

Denial of the reflex nature of instinctive acts led some researchers to define them as congenital, internally organized and manifested spontaneously (W. Thorpe). W. Craig suggested that instinct is associated with the accumulation of "specific energy of action", which is released by the resolving situation. At the same time, instinctive actions reflecting internal needs include the search (preparatory) and final phases.

An example is the activity of a predator when tracking and eating prey. At the first stage, there is an undirected search, then, in accordance with the stimuli emanating from the victim, the search becomes directed, followed by a series of behavioral acts (sneaking or pursuit, jumping, killing the victim, dismembering it into pieces). The second stage (eating the victim) is final (consumatory) and proceeds more stereotypically than the first. W. Craig attached great importance to drives and impulses, believing that the final stage of instinctive action suppresses them.