Define the concept of reflex. Types of reflexes

HIGH NERVOUS ACTIVITY

FUNCTIONS OF THE AUTONOMIC NERVOUS SYSTEM

Vegetative department nervous system carries out its activities on the principle of unconditioned and conditioned reflexes. All reflexes of the autonomic nervous system are called autonomic. Their number is very large and they are diverse: viscero-visceral, viscero-cutaneous, cutaneous-visceral and others. Viscero-visceral reflexes are reflexes arising from receptors internal organs on the same or other internal organs; viscero-cutaneous - from receptors of internal organs to blood vessels and other skin structures; cutano-visceral - from skin receptors to blood vessels and other structures of internal organs.

Vascular, trophic and functional influences on organs are realized through autonomic nerve fibers. Vascular influences determine the lumen of blood vessels, blood pressure, blood flow. Trophic influences regulate metabolism in tissues and organs, providing them with nutrition. Functional influences regulate functional states fabrics.

The autonomic nervous system regulates the activity of internal organs, blood vessels, sweat glands, and also regulates the trophism (nutrition) of skeletal muscles, receptors and the nervous system itself. The speed of excitation along autonomic nerve fibers is 1-3 m/s. The function of the autonomic nervous system is under the control of the cerebral cortex.

Lecture No. 4

Plan:

1. Reflex. Definition. Types of reflexes.

2. Formation of conditioned reflexes

2.1. Conditions for the formation of conditioned reflexes

2.2. The mechanism of formation of conditioned reflexes

3. Inhibition of conditioned reflexes

4. Types of higher nervous activity

5. Signal systems

Higher nervous activity (HNA) is the joint activity of the cerebral cortex and subcortical formations, which ensures the adaptation of human behavior to changing environmental conditions.

Higher nervous activity is carried out according to the principle of a conditioned reflex and is usually called conditioned reflex activity. In contrast to the VND, the nervous activity of the lower parts of the central nervous system is carried out according to the principle of an unconditioned reflex. It is the result of the activity of the lower parts of the central nervous system (dorsal, medulla oblongata, midbrain, diencephalon and subcortical nuclei).

The idea of the reflex nature of the activity of the cerebral cortex and its connection with consciousness and thinking was first expressed by the Russian physiologist I.M. Sechenov. The main provisions of this idea are contained in his work “Reflexes of the Brain”. His idea was developed and experimentally proven by Academician I.P. Pavlov, who developed methods for studying reflexes and created the doctrine of unconditioned and conditioned reflexes.

Reflex(from Latin reflexus - reflected) - a stereotypical reaction of the body to a certain impact, taking place with the participation of the nervous system.

Unconditioned reflexes- these are innate reflexes, formed in the process of evolution of a given species, transmitted by inheritance, and carried out according to innate nerve pathways, with nerve centers in the underlying parts of the central nervous system (for example, the reflex of sucking, swallowing, sneezing, etc.). Irritants that cause unconditioned reflexes are called unconditional.

Conditioned reflexes- these are reflexes acquired during the individual life of a person or animal, and are carried out with the participation of the cerebral cortex as a result of a combination of indifferent (conditioned, signal) stimuli with unconditioned ones. Conditioned reflexes are formed on the basis of unconditioned ones. Stimuli that cause conditioned reflexes are usually called conditioned.

Reflex arc(nerve arc) - the path traversed by nerve impulses during the implementation of a reflex

Reflex arc comprises:

receptor - a nerve link that perceives irritation

· afferent link - centripetal nerve fiber - processes of receptor neurons that transmit impulses from sensory nerve endings to the central nervous system

central link - nerve center (optional element, for example for the axon reflex)

· efferent link - centrifugal nerve fiber that conducts excitation from the central nervous system to the periphery

· effector - an executive organ whose activity changes as a result of a reflex.

There are: - monosynaptic, two-neuron reflex arcs; - polysynaptic reflex arcs (include three or more neurons).

The concept was introduced by M. Hall in 1850. Today, the concept of a reflex arc does not fully reflect the mechanism of the reflex, and in this regard, N.A. Bernstein proposed a new term - a reflex ring, which includes the missing link of control exercised by the nerve center over the progress of the executive organ - the so-called. reverse afferentation.

The simplest reflex arc in humans, it is formed by two neurons - sensory and motor (motoneuron). An example of a simple reflex is the knee reflex. In other cases, three (or more) neurons are included in the reflex arc - sensory, intercalary and motor. In a simplified form, this is the reflex that occurs when a finger is pricked with a pin. This is a spinal reflex; its arc passes not through the brain, but through the spinal cord. The processes of sensory neurons enter the spinal cord as part of the dorsal root, and the processes of motor neurons exit from spinal cord as part of the front one. The bodies of sensory neurons are located in the spinal ganglion of the dorsal root (in the dorsal ganglion), and intercalary and motor ones are in gray matter spinal cord. The simple reflex arc described above allows a person to automatically (involuntarily) adapt to change environment, for example, withdrawing your hand from a painful stimulus, changing the size of the pupil based on lighting conditions. It also helps regulate processes occurring inside the body. All this helps to maintain consistency internal environment, that is, maintaining homeostasis. In many cases, a sensory neuron transmits information (usually through several interneurons) to the brain. The brain processes incoming sensory information and stores it for later use. Along with this, the brain can send motor nerve impulses along the descending pathway directly to the spinal motor neurons; spinal motor neurons initiate the effector response.

The concept of reflex is very important in physiology. This concept explains the automated work of the body to quickly adapt to changes in the environment.

With the help of reflexes, the nervous system coordinates the activities of the body with signals coming from the surrounding external and internal environment.

Reflex (reflection) is the basic principle and way of working of the nervous system. More general concept - reactivity . These concepts imply that the reason for the behavioral activity of the organism lies not in the psyche, but out of psyche , outside the nervous system, and is triggered by signals external to the psyche and the nervous system - stimuli. Also implied determinism , i.e. predetermination of behavior due to the cause-and-effect relationship between the stimulus and the body’s response to it.

The concepts of “reflex” and “reflex arc” relate to the field of physiology of the nervous system and they must be understood to the level of complete understanding and clarity in order to understand many other topics and sections of physiology.

Definition of the concept

A simple definition of the concept "reflex"

Reflex is responsiveness. You can give such a definition to a reflex, but after that it is necessary to name 6 important criteria (signs) of a reflex that characterize it. They are listed below in full definition reflex concepts.

A reflex is a stereotypical automated adaptive responsiveness to a stimulus (irritant).

A reflex in a general broad sense is secondary a phenomenon caused by another phenomenon (primary), i.e. reflection, a consequence in relation to something original. In physiology, a reflex is responsiveness the body to an incoming signal, the source of which is outside the psyche, when the triggering signal (stimulus) is the primary phenomenon, and the reaction to it is secondary, response.

A complete definition of the concept "reflex"

Physiological definition of the concept "reflex arc"

Reflex arc - this is a schematic path of excitation movement from the receptor to the effector.

We can say that this is the path of nervous excitation from the place of its birth to the place of application, as well as the path from the information input to the information output from the body. This is what a reflex arc is from a physiological point of view.

Anatomical definition of the concept "reflex arc"

Reflex arc - this is a set of nervous structures involved in the implementation of a reflex act.

Both of these definitions of the reflex arc are correct, but for some reason the anatomical definition is more often used, although the concept of a reflex arc refers to physiology, not anatomy.

Remember that the diagram of any reflex arc must begin with irritant , although the stimulus itself is not part of the reflex arc. The reflex arc ends with the organ effector , which gives a response.

Stimulus - it's such physical factor, which, when exposed to sensory receptors adequate for it, generates nervous excitement in them.

The stimulus triggers transduction in the receptors, as a result of which irritation is converted into excitation.

Electric current is a universal stimulus because it can generate excitation not only in sensory receptors, but also in neurons, nerve fibers, glands and muscles.

Variants of the result of the effect of an irritant on the body

1. Launching an unconditioned reflex.

2. Triggering a conditioned reflex.

3. Launch of the orientation reflex.

4. Launching the dominant.

5. Launch of a functional system.

6. Triggering emotions.

7. Launching the creation of a neural model (in particular, a sensory image), the learning/memorization process.

8. Trigger memories.

There are not many types of effectors.

Types of effectoro V:

1) striated muscles of the body (fast white and slow red),

2) smooth muscles of blood vessels and internal organs,

3) exocrine glands (for example, salivary glands),

4) endocrine glands (for example, adrenal glands).

Accordingly, responses will be the result of the activity of these effectors, i.e. contraction or relaxation of muscles, leading to movements of the body or internal organs and blood vessels, or secretion of secretions by glands.

Concept of temporary neural connection

“A temporary connection is a set of biochemical, neurophysiological and, possibly, ultrastructural changes in the brain that arise in the process of combining conditioned and unconditioned stimuli and form strictly defined relationships between structural formations that underlie various brain mechanisms. The memory mechanism records these relationships, ensuring their retention and reproduction." (Khananashvili M.M., 1972).

Meanwhile, the meaning of this tricky definition boils down to the following:

Temporary neural connection - this is the flexible part catch reflex arc, formed during the development of a conditioned reflex to connect two undoubtedly reflex arcs. It ensures the conduction of excitation between the nerve centers of two different unconditioned reflexes. Initially, one of these two unconditioned reflexes is triggered by a weak stimulus ("conditioned"), and the second by a strong one ("unconditioned" or "reinforcement"), but when a conditioned reflex has already been developed, the weak conditioned stimulus gets the opportunity to trigger an "alien" unconditioned reaction for due to the transition of excitation from its nerve center to the nerve center of a strong unconditioned stimulus.

Types of reflex arcs:

This reflex arc is the simplest, it contains only 5 elements. Although the figure shows more elements, from them we identify 5 main and necessary ones: receptor (2) - afferent ("carrying") neuron (4) - intercalary neuron (6) - efferent ("carrying out") neuron (7, 8 ) - effector (13).

It is important to understand the meaning of each element of the arc. Receptor : converts irritation into nervous excitement. Afferent neuron : delivers sensory stimulation to the central nervous system, to the interneuron. Interneuron : transforms the incoming excitement and directs it along the desired path. So, for example, an interneuron can receive sensory ("signal") excitation, and then transmit another excitation - motor ("control"). Efferent neuron : delivers control excitation to the effector organ. For example, motor excitation - on a muscle. Effector carries out a response.

The figure on the right shows a rudimentary reflex arc using the example of the knee reflex, which is so simple that it does not even have interneurons.

Please note that on the motor neuron that ends the reflex arc, many endings of neurons located on different levels nervous system and seeking to control the activity of this motor neuron.

4. Double sided arc conditional reflex E.A. Asratyan. It shows that during the development of a conditioned reflex, opposing temporary connections are formed and both stimuli used are simultaneously both conditioned and unconditioned.

The figure on the right shows an animated diagram of a double conditioned reflex arc. It actually consists of two unconditioned reflex arcs: the left one is a blinking unconditioned reflex to irritation of the eye by an air flow (the effector is the contracting muscle of the eyelid), the right one is the salivary unconditioned reflex to irritation of the tongue with acid (the effector is salivary gland secreting saliva). Due to the formation of temporary conditioned reflex connections in the cerebral cortex, effectors begin to respond to stimuli that are normally inadequate for them: blinking in response to acid in the mouth and salivation in response to blowing air into the eye.

5. Reflex ring ON THE. Bernstein. This diagram shows how movement is reflexively adjusted depending on the achievement of the set goal.

6. Functional system to ensure appropriate behavior of P.K. Anokhina. This diagram shows the management of complex behavioral acts aimed at achieving a useful planned result. The main features of this model: action result acceptor and feedback between elements.

7. Double arc of the conditioned salivary reflex. This diagram shows that any conditioned reflex must consist of two reflex arcs formed by two different unconditioned reflexes, because Each stimulus (conditioned and unconditioned) generates its own unconditioned reflex.

An example of an experimental protocol for developing a conditioned pupillary reflex to sound in a laboratory lesson

Experience no.	UR (conditioned stimulus), inadequate for the pupil	CPR (conditioned response) of the pupil	BR (unconditioned stimulus), adequate for the pupil	BOR (unconditioned response) of the pupil	Note
Stimuli and reactions	Sound (knock or ringing bell)	Extension/Narrowing pupil	Darkness/Light(darkening one eye)	Extension/Narrowing pupil	Unconditional response to sound We don’t register it, even if it exists. We evaluate only the reaction to darkening.
*Series 1. Obtaining an unconditional response to darkness in the form of pupil dilation*
1.	(-)	(-)	(+)	(+)	Only BOR is observed
…	(-)	(-)	(+)	(+)	Only BOR is observed
10.	(-)	(-)	(+)	(+)	Only BOR is observed
Conclusion : An unconditional response of the pupil to an adequate BR (darkness) is constantly manifested.
*Series 2. Obtaining an indifferent (indifferent) action of an inadequate conditioned stimulus (sound) on the pupil*
1.	(+)	(+) ?	(-)	(+) ?
2.	(+)	(+)	(-)	(+)	OER (indicative response)
…	(+)	(+)	(-)	(+)	OER (indicative response)
10.	(+)	(-)	(-)	(-)	The stimulus is already indifferent
Conclusion : After several repetitions of irritation that is inadequate for the pupil, the OOR disappears and the irritant becomes indifferent (indifferent).
*Series 3. Development of a conditioned reflex (conditioned response)*
1.	(+)	(-)	(+)	(+)	Only BOR is observed
…	(+)	(-)	(+)	(+)	Only BOR is observed
15.	(+)	(+)	(+)	(+)	UOR appears
16.	(+)	(+)	(-)	(-)	UOR (conditioned response) appears even in the absence of UOR (unconditioned response)
Conclusion : After repeated combinations of conditioned and unconditioned stimuli, a conditioned response of the pupil appears to a previously indifferent conditioned stimulus (sound).
*Series 4. Obtaining inhibition of the conditioned reflex (extinction)*
1.	(+)	(+)	(-)	(-)
…	(+)	(+)	(-)	(-)	COR is observed (conditioned response)
6.	(+)	(-)	(-)	(-)
Conclusion : After repeated conditioned stimuli without reinforcement with unconditioned stimuli, the EOR disappears, i.e. the conditioned reflex is inhibited.
*Series 5. Secondary development (restoration) of an inhibited conditioned reflex*
1.	(+)	(-)	(+)	(+)	Only BOR is observed
…	(+)	(-)	(+)	(+)	Only BOR is observed
5.	(+)	(+)	(+)	(+)	UOR appears
6.	(+)	(+)	(-)	(-)	UOR (conditioned response) manifests itself in the absence of the BR (unconditioned stimulus) and the BOR (unconditioned response) caused by it.
Conclusion : Secondary development (restoration) of conditioned reflexes occurs faster than the initial development.
*Series 6. Obtaining secondary inhibition of conditioned reflexes (repeated extinction)*
1.	(+)	(+)	(-)	(-)	COR is observed (conditioned response)
…	(+)	(+)	(-)	(-)	COR is observed (conditioned response)
4.	(+)	(-)	(-)	(-)	Disappearance of the conditioned response
Conclusion: Secondary inhibition of the conditioned reflex is developed faster than its primary inhibition.
Designations: (-) - absence of irritation or reaction, (+) - presence of irritation or reaction

When classifying the diverse reflexes of the human and animal body, they are taken into account various signs and manifestations. All reflexes by origin are divided into unconditional (congenital or specific) and conditional (acquired during the individual life of an animal or a person, developed under certain conditions).

Based biological significance reflexes for the body are divided into:

- on protective, aimed at moving away from the stimulus;
– food, ensuring the acquisition, consumption and digestion of food;
– sexual, ensuring continuation of the family;
– indicative, or research, ensuring body rotation and movement towards a new stimulus;
– postural-tonic, or reflexes of body position in space ;
– locomotor, providing movement of the body in space.

Depending on the location of the reflex arc receptors, there are:

– exteroceptive reflexes that occur in response to irritation of body surface receptors;
– proprioceptive reflexes that occur in response to irritation of receptors in muscles, tendons and joints;
– visceroceptive reflexes that occur in response to irritation of receptors of internal organs.

Depending on the organs whose activity is ensured by this reflex, cardiac, respiratory, vascular and other reflexes are distinguished.

Reflexes are also distinguished by the nature of the responses: secretory, expressed in the release of secretion produced by the gland; trophic, associated with changes in metabolism; motor, or motor, characterized by the contractile activity of striated and smooth muscles (the most diverse group of reflexes). Motor reflexes include flexion, rubbing, scratching reflexes and others that occur when the skin is irritated; sucking reflex in a child; protective reflex when the cornea of the eye is irritated - blinking; pupillary reflex - constriction of the pupil when exposed to light and dilation in the dark.

Motor proprioceptive reflexes occur when muscle and tendon receptors are stimulated. So, when the tendon of the quadriceps femoris is hit, as a result of its stretching, a reflex extension of the leg at the knee occurs - the knee reflex; when the Achilles tendon is hit - the Achilles reflex.

Vasomotor reflexes involve the constriction and dilation of blood vessels.

Visceromotor reflexes are motor reflexes that occur when the smooth muscle receptors of internal organs are stimulated; they provide movement of the stomach, intestines, Bladder, ureters, etc.

All the reflexes described above, depending on which parts of the central nervous system are involved in their implementation, are divided:

- on spinal (carried out with the participation of spinal cord neurons);
– bulbar (involving neurons medulla oblongata);
– mesencephalic (involving the midbrain);
– diencephalic (involving the diencephalon);
– cortical (with the participation of neurons in the cerebral cortex).

Spinal reflexes include flexion, which occurs when pinching a frog’s leg with tweezers, rubbing, which occurs when the frog’s skin is irritated with a piece of paper soaked in sulfuric acid, etc., as well as reflexes from the tendons of the limbs. The sucking and blinking reflexes are carried out with the participation of the medulla oblongata, and the pupillary reflexes - the midbrain.

The regulation of any function involves the participation of different parts of the central nervous system, therefore the classification of reflexes according to the parts of the brain involved in their implementation is relative. We are talking only about the leading importance of neurons of one or another part of the central nervous system.

Inhibition in the central nervous system- an active process manifested in the suppression or weakening of excitation. Unlike excitation, inhibition does not spread along nerve fibers.

The phenomenon of inhibition in nerve centers was described by I.M. Sechenov in 1862. Much later, the English physiologist Sherrington discovered that the processes of excitation and inhibition are involved in any reflex act.

Braking value:

– coordination - the process of inhibition ensures orderliness or coordination in the work of nerve centers, for example, to bend an arm, it is necessary to excite the flexion center, which sends nerve impulses to the biceps, and inhibit the extension center, which sends nerve impulses to the triceps;
– protective – under the influence of super-strong stimuli in the nerve center, not excitation, but inhibition develops, as a result, reserves of ATP and transmitter are restored;
– limitation the influx of afferent impulses into the central nervous system of secondary information of little significance for life.

There are presynaptic and postsynaptic inhibition. With presynaptic inhibition, the inhibitory effect is realized on the presynaptic membrane; this type of inhibition is involved in limiting the influx of sensory impulses into the brain. Postsynaptic inhibition occurs on the postsynaptic membrane. This is the main type of inhibition; it develops in special inhibitory synapses with the participation of inhibitory transmitters, which suppress the ability of a nerve cell to generate excitation processes.

According to neural organization, inhibition is divided into translational, recurrent, lateral (side) and reciprocal.

1. Progressive inhibition is caused by the inclusion of inhibitory neurons along the path of excitation.
2. Returnable inhibition is carried out by intercalary inhibitory neurons (Renshaw cells). Impulses from motor neurons through collaterals extending from its axon activate the Renshaw cell, which, in turn, causes inhibition of the discharges of this neuron. This inhibition is realized due to inhibitory synapses formed by the Renshaw cell on the body of the motor neuron that activates it. Thus, a circuit with negative feedback is formed from two neurons, which makes it possible to suppress excessive activity of the motor neuron.
3. Lateral inhibition is the process of inhibiting a group of neurons located next to a group of excited cells. This type of inhibition is common in sensory systems.
4. Reciprocal, or conjugate, inhibition is based on the fact that the signals are on the same afferent pathways provide excitation of one group of neurons, and through intercalary inhibitory cells cause inhibition of another group of neurons. It manifests itself, for example, at the level of motor neurons of the spinal cord innervating antagonist muscles (flexors - extensors of the limbs). When bending an arm or leg, the centers of the extensor muscles are inhibited. A reflex act is possible only with conjugate inhibition of antagonist muscles. When walking, bending the leg is accompanied by relaxation of the extensors, and vice versa, when extending, the flexor muscles are inhibited. If this did not happen, then a mechanical struggle of the muscles, convulsions, would arise, and not adaptive motor acts. Violation of reciprocal inhibition underlies motor disorders accompanying many motor development disorders in childhood.

During ontogenesis, due to the development of inhibitory neurons, inhibitory mechanisms of the central nervous system are formed. Their early form is postsynaptic inhibition, later presynaptic inhibition is formed. Thanks to the formation of inhibitory mechanisms, the irradiation of excitation into the central nervous system, characteristic of newborns, is significantly limited, unconditioned reflexes become more accurate and localized.

Coordination of reflex activity- this is the coordinated interaction of nerve centers to ensure any process. Coordination of functions ensures reflex acts that correspond to environmental influences and are manifested by various systems (muscular, endocrine, cardiovascular). For example, when running, the flexor and extensor muscles reflexively work, blood pressure rises, the lumen of blood vessels increases, and the heartbeat and breathing become more frequent. Coordination of functions is determined by the characteristics of the relationship between reflex manifestations on the part of various body systems for the implementation of a certain physiological act. Coordination mechanisms develop throughout childhood and reach their perfection by the age of 18-20.

Mechanisms for coordinating reflex activity:

1. Irradiation of excitation. Neurons of different centers are interconnected by numerous interneurons, therefore, when receptors are stimulated, excitation can spread not only to the neurons of the center of a given reflex, but also to other neurons (the phenomenon of irradiation). The stronger and longer the afferent stimulation and the higher the excitability of surrounding neurons, the more neurons the irradiation process covers. Inhibition processes limit irradiation and contribute to the concentration of excitation at the starting point of the central nervous system.

The process of irradiation plays an important positive role in the formation of new reactions of the body (indicative reactions, conditioned reflexes). Thanks to the irradiation of excitation between different nerve centers, new functional connections arise - conditioned reflexes. Excessive irradiation of excitation can have a negative impact on the state and actions of the body, disrupting the delicate relationships between excited and inhibited nerve centers and causing impaired coordination of movements.

2. Relief and occlusion. Facilitation is the excess of the effect of the simultaneous action of two weak stimuli over the sum of their separate effects. Occlusion (blockage) is the opposite phenomenon of relief. Occlusion occurs under the influence of strong stimuli and leads to a decrease in the strength of the total response.
3. The principle of a common final path. There are several times more afferent neurons in the central nervous system than efferent ones. In this regard, different afferent influences arrive at the same intercalary and efferent neurons, which are their common final paths to the working organs. Many different stimuli can cause the same motor neurons in the spinal cord to act. For example, motor neurons that control the respiratory muscles, in addition to providing inhalation, are involved in reflex reactions such as sneezing, coughing, etc.

Distinguish allied And antagonistic reflexes (first identified by the English physiologist C. Sherrington, who established the principle of a common final path). Meeting on common final paths, allied reflexes mutually reinforce each other, and antagonistic reflexes inhibit each other. In the first case, in the neurons of the common terminal pathway, nerve impulses are summed up (for example, the flexion reflex is enhanced by simultaneous irritation of several areas of the skin). In the second case, competition occurs for the possession of a common final path, as a result of which only one reflex is carried out, while the others are inhibited. The ease of performing mastered movements is explained by the fact that they are based on time-ordered, synchronized flows of impulses that pass through finite paths more easily than impulses arriving in a random order.

The predominance of one or another reflex reaction on the final paths is determined by its significance for the life of the organism at a given moment. In such selection, the presence of a dominant in the central nervous system plays an important role (see below). It ensures the occurrence of the main reaction, suppressing secondary ones.

4. Feedback, or secondary afferentation. Any motor act caused by an afferent stimulus is accompanied by excitation of receptors in muscles, tendons, and joint capsules. Signals from proprioceptors secondarily enter the central nervous system, which allows for correction of its activity and self-regulation in accordance with the current needs of the body and the environment. This important principle of reflex self-regulation of body functions is called the feedback principle. In addition, due to feedback, the tone of the nerve centers is maintained.
5. Reciprocal (conjugate) relationships between nerve centers. The basis of the relationship between nerve centers is the process of induction - stimulation (induction) of the opposite process. Induction limits the spread (irradiation) of nervous processes and ensures the concentration of excitation.

There are simultaneous and sequential induction. A strong excitation process in a nerve center causes (induces) inhibition in neighboring nerve centers, and a strong inhibitory process induces excitation in neighboring nerve centers. Thus, when the extensor centers of the muscles are excited, the flexor centers are inhibited and vice versa.

When the processes of excitation and inhibition change within one center, they speak of sequential negative or positive induction. It is of great importance in organizing rhythmic activity, providing alternate contraction and relaxation of muscles, and underlies many life support acts, such as breathing and heartbeat.

In children, clear inductive relationships between the processes of inhibition and excitation begin to develop between the ages of 3 and 5 years, since at this age the strength and differentiation of nervous processes increases.

6. Dominant – temporary predominance of one nerve center or group of centers over others, determining the current activity of the body. In 1923, A. A. Ukhtomsky formulated the principle of dominance as a working principle of the activity of nerve centers.

The dominant is characterized by:

– increased excitability of the nerve centers included in the dominant focus;
– persistence of excitation of the centers of the dominant focus over time;
– the ability to enhance one’s excitation due to the summation of nerve impulses going to other centers (“attract” impulses going to other centers, as a result, irritation of various receptor fields begins to cause a reflex response characteristic of the activity of a given dominant center);
– the ability of the dominant center, through the mechanism of simultaneous induction, to cause inhibition of the activity of other centers.

A dominant focus in the central nervous system can arise under the influence various factors, in particular, strong afferent stimulation, hormonal influences, changes in blood chemistry, motivation, etc. The central nervous system has the ability to rearrange dominant relationships in accordance with the changing needs of the body, and throughout a person’s life, one dominant replaces another.

A dominant focus in a child arises faster and easier than in adults, but it is characterized by low resistance to external stimuli. This is largely associated with the instability of attention in children: new stimuli easily evoke a new dominant, and indicative reactions themselves early age are dominant.

7. Plastic nerve centers - functional variability and adaptability of nerve centers, their ability to perform new, unusual reflex acts. This is especially pronounced after removal of various parts of the brain. If some parts of the cerebellum or cerebral cortex were partially removed, the impaired function may be partially or completely restored over time.

(lat. reflexus - turned back, reflected) - the body’s response to certain influences carried out through the nervous system. There are R. unconditional (congenital) and conditional (acquired by the body during an individual life, having the property of disappearing and being restored). Fr. philosopher R. Descartes was the first to point out the reflex principle in brain activity. N.D. Naumov

Excellent definition

Incomplete definition ↓

REFLEX

from lat. reflexus – turning back; V figurative meaning– reflection) – general principle regulation of the behavior of living systems; engine (or secretory) act that has an adaptability. meaning determined by the influence of signals on receptors and mediated by nerve centers. The concept of R. was introduced by Descartes and served the task of deterministically explaining, within the framework of mechanism. pictures of the world, the behavior of organisms based on the general laws of physics. interaction of macrobodies. Descartes rejected the soul as he explains. motor principle activity of the animal and described this activity as the result of a strictly natural response of the “machine-body” to external influences. Based on the mechanistically understood principle of R., Descartes tried to explain certain mental. functions, in particular learning and emotions. All subsequent neuromuscular physiology was under the determining influence of the doctrine of R. Some followers of this doctrine (Dilli, Swammerdam) back in the 17th century. expressed a guess about the reflexive nature of all human behavior. This line was completed in the 18th century. La Mettrie. Ch. the enemy of deterministic view of R. came out with vitalism (Stahl and others), which argued that not a single organic. the function is not carried out automatically, but everything is directed and controlled by the sentient soul. In the 18th century Witt discovered that dep. a segment of the spinal cord is sufficient to carry out an involuntary muscle reaction, but he considered its determinant to be a special “sensitive principle”. The problem of the dependence of movement on sensation, used by Witt to prove the primacy of feeling in relation to the work of the muscle, materialistic. the interpretation was given by Hartley, who pointed out that sensation actually precedes movement, but it itself is caused by a change in the state of moving matter. Opening specific. signs of neuromuscular activity prompted naturalists to introduce the concept of “forces” inherent in the body and distinguishing it from other natural bodies (“muscular and nervous force” by Haller, “nervous force” by Unzer and Prohaska), and the interpretation of force was materialistic. Creatures contribution to the further development the doctrine of R. was introduced by Prohaska, who proposed the biological. R.'s explanation as a purposeful act regulated by a sense of self-preservation, under the influence of which the body evaluates external stimuli. The development of the anatomy of the nervous system led to the discovery of the mechanism of the simplest reflex arc (Bell-Magendie law). A scheme for the localization of reflex pathways emerges, based on the cut in the 30s. 19th century the classic is maturing. the doctrine of R. as the principle of operation of the spinal centers, in contrast to the higher parts of the brain. It was substantiated by Marshall Hall and I. Muller. This is purely physiological. the teaching exhaustively explained the definition. category of nervous acts by the influence of an external stimulus on a specific. anatomical structure. But the idea of R. as mechanical. "blind" movement, predetermined anatomically. structure of the organism and independent of what happens in external environment, forced us to resort to the idea of a force that selects from a set of reflex arcs those needed in given circumstances and synthesizes them into a holistic act in accordance with the object or situation of action. This concept has been subjected to sharp experimental-theoretical research. criticism from materialistic positions by Pflueger (1853), who proved that lower vertebrates, lacking a brain, are not purely reflex automata, but vary their behavior with changing conditions, which, along with reflex function there is a sensory one. Weak side Pflueger's position was opposed to R. sensory function, the transformation of the latter into the finite will explain. concept. Sechenov brought the theory of R. to a new path. The former is purely morphological. He transformed R.’s scheme into a neurodynamic one, bringing the center connection to the foreground. processes in natural groups. The regulator of movement was recognized as feeling of varying degrees of organization and integration - from the simplest sensation to the dismembered sensory, and then the mind. an image that reproduces the objective characteristics of the environment. Accordingly, the afferent phase of the interaction of the organism with the environment was not thought of as mechanical. contact, but as the acquisition of information that determines the subsequent course of the process. The function of the centers was interpreted in a broad biological sense. adaptation. Engine activity acted as a factor that has a reverse influence on the construction of behavior - external and internal (feedback principle). Subsequently, a major contribution to the development of physiological. ideas about the mechanism of R. were introduced by Sherrington, who studied the integrative and adaptive originality of nervous acts. However, in the understanding of mental he adhered to dualistic functions of the brain. views. I.P. Pavlov, continuing the line of Sechenov, experimentally established the difference between unconditional and conditional R. and discovered the laws and mechanisms of reflex work of the brain, forming physiological. basis of mental activities. Subsequent study of complex adaptations. acts supplemented general scheme R. with a number of new ideas about the mechanism of self-regulation (N. A. Bernstein, P. K. Anokhin, etc.). Lit.: Sechenov I.M., Physiology of the nervous system, St. Petersburg, 1866; Immortal B.S., One Hundred Years of the Belle-Magendie Doctrine, in the book: Archives of Biol. Sciences, vol. 49, no. 1, ?., 1938; Conradi G.P., On the history of the development of the doctrine of R., ibid., vol. 59, no. 3, M., 1940; Anokhin P.K., From Descartes to Pavlov, M., 1945; Pavlov I. P., Izbr. works, M., 1951; Yaroshevsky M. G., History of Psychology, M., 1966; Gray Walter W., The Living Brain, trans. from English, M., 1966; Eckhard S., Geschichte der Entwicklung der Lehre von den Reflexerscheinungen, "Beitr?ge zur Anatomie und Physiologie", 1881, Bd 9; Fulton J. F., Muscular contraction and the reflex control of movement, L., 1926; Fearing F., Reflex action. A study in the history of physiological psychology, L., 1930; Bastholm E., The history of muscle physiology, Copenhagen, 1950. M. Yaroshevsky. Leningrad. Current state teachings about R. Advances in the physiology of the nervous system and the close contact of general neurophysiology and the physiology of higher nervous activity with biophysics and cybernetics have extremely expanded and deepened the understanding of R. at the physicochemical, neural, and system levels. Physico-chemical level. An electron microscope showed the subtle mechanism of the chemical. transferring excitation from neuron to neuron by emptying transmitter bubbles into the synaptic. cracks (E. de Robertis, 1959). At the same time, the nature of the excitation wave in the nerve is determined, as 100 years ago by L. Herman (1868), in the form of physical. action current, short-term electric impulse (B. Katz, 1961). But along with electrical ones, metabolic ones are taken into account. excitation components, e.g. "sodium pump" generating electricity. current (A. Hodgkin and A. Huxley, 1952). Neural level. Even Ch. Sherrington (1947) associated certain properties of simple spinal R., for example. reciprocity of excitation and inhibition, with a hypothetical neuron connection diagrams. I. S. Beritashvili (1956) based on cytoarchitectonic. data made a number of assumptions about various forms organization of neurons in the cerebral cortex, in particular about the reproduction of images of the external world by the system stellate cells sees analyzer of lower animals. General theory the neural organization of reflex centers was proposed by W. McCulloch and V. Pite (1943), who used the mathematical apparatus. logic for modeling the functions of neural circuits in a rigidly deterministic manner. networks of formal neurons. However, many The properties of higher nervous activity do not fit into the theory of fixed nerve networks. Based on the results of electrophysiological. and morphological studying the interconnection of neurons in the higher parts of the brain, a hypothesis of their probabilistic-statistical organization is developed. According to this hypothesis, the regularity of the reflex reaction is ensured not by the unambiguous path of signals along fixed interneuron connections, but by the probabilistic distribution of their flows across sets. ways and statistical way to achieve the final result. Randomness in the interaction of neurons was assumed by D. Hebb (1949), A. Fessar (1962) and other researchers, and W. Gray Walter (1962) showed statistical data. the nature of conditional R. Often neural networks with fixed connections are called deterministic, contrasting them with networks with random connections as indeterministic. However, stochasticity does not mean indeterminism, but, on the contrary, provides the highest, most flexible form of determinism, which apparently lies at the basis of the Holy Rule. plasticity R. System level. The system of even simple unconditional R., for example. pupillary, consists of a number of self-regulating subsystems with linear and nonlinear operators (M. Clynes, 1963). The assessment of the correspondence between the acting stimuli and the “nervous model of the stimulus” (E. N. Sokolov, 1959) turned out to be important factor biologically expedient organization of R. Taking into account the mechanisms of self-regulation by feedback, the presence of which was written by Sechenov (1863), the structure of R. in modern times. cybernetic aspect began to be represented not as an open reflex arc, but as a closed reflex ring (N.A. Bernstein, 1963). IN Lately discussions arose about the content of the concepts of signaling, reinforcement and temporary connections of conditional R. Thus, P.K. Anokhin (1963) considers signaling as a manifestation of the work of the mechanism for “predicting” events in the external world, and reinforcement as the formation of cyclical. structures for monitoring the results of action. E. A. Asratyan (1963) emphasizes qualities. differences between the connections of conditional R. and short-term ones. reactions such as trampling and dominance. Lit.: Beritashvili I. S., Morphological. and physiological foundations of temporary connections in the cerebral cortex, "Tr. Institute of Physiology named after I. S. Beritashvili", 1956, vol. 10; McCulloch, W. S. and Pitts, W., Logic. calculus of ideas relating to nervous activity, [trans. from English], in the collection: Avtomaty, M., 1956; Sokolov E.N., Nervous model of stimulus, "Doc. APN RSFSR", 1959, No. 4; Katz B., The nature of the nerve impulse, in: Sovrem. problems of biophysics, vol. 2, M., 1961; Hartline X., Receptor mechanisms and integration of sensory information in the retina, ibid.; Walter G. W., Stat. approach to the theory of conditioned R., in the book: Electroencephalographic. study of higher nervous activity, M., 1962; Fessar?., Analysis of the closure of temporary connections at the neuronal level, ibid.; Smirnov G.D., Neurons and functional. organization of the nerve center, in: Gagra Conversations, vol. 4, Tb., 1963; Philosophy question Physiology of Higher Nervous Activity and Psychology, M., 1963 (see article by P.K. Anokhin, E.A. Asratyan and N.A. Bernstein); Kogan A. B., Probabilistic-statistical. principle of neural organization functional systems brain, "DAN USSR", 1964, vol. 154, No. 5; Sherrington Ch. S., The integrative action of the nervous system, , 1947; Hodgkin A. L., Huxley A. F., A quantitative description of membrane current and its application to conduction and excitation in nerve, "J. physiol.", 1952, v. 117, No. 4; Hebb D. O., The organization of behavior, N. Y.–L., ; Robertis Ed. de, Submicroscopic morphology of the synapse, "Intern. Rev. Cytol.", 1959, v. 8, p. 61–96. A. Kogan. Rostov n/a.

The nervous system operates on the principle of unconditioned and conditioned reflexes. All reflexes of the autonomic nervous system are called autonomic. Their number is very large and they are diverse: viscero-visceral, viscero-cutaneous, cutaneous-visceral and others.

Viscero-visceral reflexes are reflexes that arise from receptors of internal organs to the same or other internal organs;

Viscero-cutaneous - from receptors of internal organs to blood vessels and other skin structures;

Cutano-visceral - from skin receptors to blood vessels and other structures of internal organs.

Vascular, trophic and functional influences on organs are carried out through autonomic nerve fibers. Vascular influences determine the lumen of blood vessels, blood pressure, and blood flow. Trophic influences regulate metabolism in tissues and organs, providing them with nutrition. Functional influences regulate the functional states of tissues.

Plan:

1. Reflex. Definition. Types of reflexes.

2. Formation of conditioned reflexes:

2.1. Conditions for the formation of conditioned reflexes

2.2. The mechanism of formation of conditioned reflexes

3. Inhibition of conditioned reflexes

4. Types of higher nervous activity

5. Signal systems

Higher nervous activity ( GNI) is the joint activity of the cerebral cortex and subcortical formations, which ensures the adaptation of human behavior to changing environmental conditions.

Higher nervous activity is carried out according to the principle of a conditioned reflex and is also called conditioned reflex activity. In contrast to the VND, the nervous activity of the lower parts of the central nervous system is carried out according to the principle of an unconditioned reflex. It is the result of the activity of the lower parts of the central nervous system (dorsal, medulla oblongata, midbrain, diencephalon and subcortical nuclei).

The idea of the reflex nature of the activity of the cerebral cortex and its connection with consciousness and thinking was first expressed by a Russian physiologist I. M. Sechenov. The main provisions of this idea are contained in his work “Reflexes of the Brain.” His idea was developed and experimentally proven by academician I. P. Pavlov, who developed methods for studying reflexes and created the doctrine of unconditioned and conditioned reflexes.

Reflex(from Latin reflexus - reflected) - a stereotypical reaction of the body to a certain impact, taking place with the participation of the nervous system.

Unconditioned reflexes- these are innate reflexes, formed in the process of evolution of a given species, transmitted by inheritance, and carried out along innate nerve pathways, with nerve centers in lower departments Central nervous system (for example, reflex of sucking, swallowing, sneezing, etc.). Stimuli that cause unconditioned reflexes are called unconditioned.

Reflex arc(nerve arc) - the path traversed by nerve impulses during the implementation of a reflex

Reflex arc comprises:

Receptor - a nerve link that perceives irritation;

Afferent link - centripetal nerve fiber - processes of receptor neurons that transmit impulses from sensory nerve endings to the central nervous system;

The central link is the nerve center (an optional element, for example for the axon reflex);

Efferent link - centrifugal nerve fiber that conducts excitation from the central nervous system to the periphery;

An effector is an executive organ whose activity changes as a result of a reflex.

Distinguish:

Monosynaptic, two-neuron reflex arcs;

Polysynaptic reflex arcs (include three or more neurons).

Concept introduced M. Hall in 1850. Currently, the concept of a reflex arc does not fully reflect the mechanism of the reflex, and in this regard Bernstein N. A. a new term was proposed - a reflex ring, which includes the missing link of control exercised by the nerve center over the progress of the executive organ - the so-called. reverse afferentation.

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

The processes of sensory neurons enter into spinal cord as part of the dorsal root, and the processes of motor neurons leave the spinal cord as part of the anterior one. The bodies of sensory neurons are located in the spinal ganglion of the dorsal root (in the dorsal ganglion), and intercalary and motor neurons are located in the gray matter of the spinal cord. The simple reflex arc described above allows a person to automatically (involuntarily) adapt to changes in the environment, for example, withdrawing a hand from a painful stimulus, changing the size of the pupil depending on lighting conditions. It also helps regulate processes occurring inside the body.

All this helps maintain the constancy of the internal environment, that is, maintaining homeostasis. In many cases, a sensory neuron transmits information (usually through several interneurons) to the brain. The brain processes incoming sensory information and stores it for later use. Along with this, the brain can send motor nerve impulses along the descending pathway directly to the spinal motor neurons; spinal motor neurons initiate the effector response.