Where is the reflex? Group "Reflex"

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.

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.

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 that developed during the evolution of a given species, are inherited, and are carried out along innate nerve pathways, with nerve centers in the underlying parts of the central nervous system (for example, the reflex of sucking, swallowing, sneezing, etc.). Stimuli that cause unconditioned reflexes are called unconditioned.

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 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;

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.

A reflex is the body's response to internal or external stimulation, carried out and controlled by the central nervous system. The first scientists who developed ideas about what was previously a mystery were our compatriots I.P. Pavlov and I.M. Sechenov.

What are unconditioned reflexes?

An unconditioned reflex is an innate, stereotypical reaction of the body to the influence of the internal or environmental environment, inherited by the offspring from the parents. It remains in a person throughout his life. Reflex arcs pass through the brain and the cerebral cortex does not take part in their formation. The significance of the unconditioned reflex is that it ensures the adaptation of the human body directly to those environmental changes that often accompanied many generations of his ancestors.

What reflexes are unconditioned?

An unconditioned reflex is the main form of activity of the nervous system, an automatic reaction to a stimulus. And since a person is influenced by various factors, the reflexes are different: food, defensive, orientation, sexual... Food include salivation, swallowing and sucking. Defensive actions include coughing, blinking, sneezing, and jerking limbs away from hot objects. Approximate reactions include turning the head and squinting the eyes. Sexual instincts include those associated with reproduction, as well as caring for offspring. The significance of the unconditioned reflex is that it ensures the preservation of the integrity of the body and maintains the constancy of the internal environment. Thanks to him, reproduction occurs. Even in newborn children, one can observe an elementary unconditioned reflex - this is sucking. By the way, it is the most important. The irritant in this case is touching the lips of any object (pacifier, mother's breast, toy or finger). Another important unconditioned reflex is blinking, which occurs when a foreign body approaches the eye or touches the cornea. This reaction belongs to the protective or defensive group. Also observed in children, for example, when exposed to strong light. However, the signs of unconditioned reflexes are most clearly manifested in various animals.

What are conditioned reflexes?

Conditioned reflexes are those acquired by the body during life. They are formed on the basis of inherited ones, subject to exposure to an external stimulus (time, knocking, light, and so on). A striking example is the experiments conducted on dogs by academician I.P. Pavlov. He studied the formation of this type of reflexes in animals and was the developer of a unique method for obtaining them. So, to develop such reactions, the presence of a regular stimulus - a signal - is necessary. It triggers the mechanism, and repeated repetition of the stimulus allows it to develop. In this case, a so-called temporary connection arises between the arcs of the unconditioned reflex and the centers of the analyzers. Now the basic instinct awakens under the influence of fundamentally new external signals. These stimuli from the surrounding world, to which the body was previously indifferent, begin to acquire exceptional, vital importance. Each living creature can develop many different conditioned reflexes during its life, which form the basis of its experience. However, this applies only to this particular individual; this life experience will not be inherited.

An independent category of conditioned reflexes

It is customary to classify into a separate category conditioned reflexes of a motor nature developed throughout life, that is, skills or automated actions. Their meaning is to master new skills, as well as develop new motor forms. For example, over the entire period of his life a person masters many special motor skills that are associated with his profession. They are the basis of our behavior. Thinking, attention, and consciousness are freed up when performing operations that have reached automaticity and become a reality of everyday life. The most successful way to master skills is to systematically perform the exercise, timely correction of noticed errors, and knowledge of the ultimate goal of any task. If the conditioned stimulus is not reinforced by the unconditioned stimulus for some time, it is inhibited. However, it does not disappear completely. If you repeat the action after some time, the reflex will be restored fairly quickly. Inhibition can also occur when a stimulus of even greater strength appears.

Compare unconditioned and conditioned reflexes

As mentioned above, these reactions differ in the nature of their occurrence and have different formation mechanisms. In order to understand what the difference is, just compare unconditioned and conditioned reflexes. Thus, the first ones are present in a living creature from birth; throughout life they do not change or disappear. In addition, unconditioned reflexes are the same in all organisms of a particular species. Their significance lies in preparing a living being for constant conditions. The reflex arc of this reaction passes through the brain stem or spinal cord. As an example, here are some (congenital): active secretion of saliva when a lemon enters the mouth; sucking movement of the newborn; coughing, sneezing, withdrawing hands from a hot object. Now let's look at the characteristics of conditioned reactions. They are acquired throughout life, can change or disappear, and, no less important, each organism has its own individual (its own). Their main function is to adapt a living creature to changing conditions. Their temporary connection (reflex centers) is created in the cerebral cortex. An example of a conditioned reflex is the reaction of an animal to a nickname or the reaction of a six-month-old child to a bottle of milk.

Unconditioned reflex diagram

According to the research of academician I.P. Pavlova, the general scheme of unconditioned reflexes is as follows. Certain receptor nerve devices are affected by certain stimuli from the internal or external world of the body. As a result, the resulting irritation transforms the entire process into the so-called phenomenon of nervous excitation. It is transmitted along nerve fibers (as if through wires) to the central nervous system, and from there it goes to a specific working organ, already turning into a specific process at the cellular level of a given part of the body. It turns out that certain stimuli are naturally connected with this or that activity in the same way as cause and effect.

Features of unconditioned reflexes

The characteristics of unconditioned reflexes presented below systematize the material presented above; it will help to finally understand the phenomenon we are considering. So, what are the features of inherited reactions?

Unconditioned instinct and reflex of animals

The exceptional constancy of the nervous connection underlying unconditional instinct is explained by the fact that all animals are born with a nervous system. She is already able to respond appropriately to specific environmental stimuli. For example, a creature may flinch at a sharp sound; he will secrete digestive juice and saliva when food enters his mouth or stomach; it will blink when visually stimulated, and so on. Innate in animals and humans are not only individual unconditioned reflexes, but also much more complex forms of reactions. They are called instincts.

An unconditioned reflex, in fact, is not a completely monotonous, template, transfer reaction of an animal to an external stimulus. It is characterized, although elementary, primitive, but still by variability, variability, depending on external conditions (strength, peculiarities of the situation, position of the stimulus). In addition, it is influenced by the internal states of the animal (decreased or increased activity, posture, etc.). So, also I.M. Sechenov, in his experiments with decapitated (spinal) frogs, showed that when the toes of the hind legs of this amphibian are exposed, the opposite motor reaction occurs. From this we can conclude that the unconditioned reflex still has adaptive variability, but within insignificant limits. As a result, we find that the balancing of the organism and the external environment achieved with the help of these reactions can be relatively perfect only in relation to slightly changing factors of the surrounding world. The unconditioned reflex is not able to ensure the animal’s adaptation to new or sharply changing conditions.

As for instincts, sometimes they are expressed in the form of simple actions. For example, the rider, thanks to his sense of smell, finds the larvae of another insect under the bark. It pierces the bark and lays its egg in the found victim. This ends all of its actions that ensure continuation of the family. There are also complex unconditioned reflexes. Instincts of this kind consist of a chain of actions, the totality of which ensures procreation. Examples include birds, ants, bees and other animals.

Species specificity

Unconditioned reflexes (specific) are present in both humans and animals. It should be understood that such reactions will be the same in all representatives of the same species. An example is a turtle. All species of these amphibians retract their heads and limbs into their shell when danger arises. And all the hedgehogs jump and make a hissing sound. In addition, you should know that not all unconditioned reflexes occur at the same time. These reactions vary with age and season. For example, the breeding season or the motor and sucking actions that appear in an 18-week fetus. Thus, unconditioned reactions are a kind of development for conditioned reflexes in humans and animals. For example, as cubs grow older, they transition to the category of synthetic complexes. They increase the body's adaptability to external environmental conditions.

Unconditional inhibition

In the process of life, each organism is regularly exposed - both from the outside and from the inside - to various stimuli. Each of them is capable of causing a corresponding reaction - a reflex. If all of them could be realized, then the life activity of such an organism would become chaotic. However, this does not happen. On the contrary, reactionary activity is characterized by consistency and orderliness. This is explained by the fact that unconditioned reflexes are inhibited in the body. This means that the most important reflex at a particular moment in time delays the secondary ones. Typically, external inhibition can occur at the moment of starting another activity. The new pathogen, being stronger, leads to the attenuation of the old one. And as a result, the previous activity will automatically stop. For example, a dog is eating, and at that moment the doorbell rings. The animal immediately stops eating and runs to meet the newcomer. There is a sharp change in activity, and the dog’s salivation stops at this moment. Unconditional inhibition of reflexes also includes some innate reactions. In them, certain pathogens cause the complete cessation of certain actions. For example, the anxious cackling of a hen makes the chicks freeze and hug the ground, and the onset of darkness forces the canary to stop singing.

In addition, there is also a protective It arises as a response to a very strong stimulus that requires the body to take actions that exceed its capabilities. The level of such influence is determined by the frequency of impulses of the nervous system. The more excited a neuron is, the higher the frequency of the stream of nerve impulses it generates. However, if this flow exceeds certain limits, then a process will arise that will begin to interfere with the passage of excitation through the neural circuit. The flow of impulses along the reflex arc of the spinal cord and brain is interrupted, resulting in inhibition that preserves the executive organs from complete exhaustion. What conclusion follows from this? Thanks to the inhibition of unconditioned reflexes, the body selects from all possible options the most adequate one, capable of protecting against excessive activity. This process also contributes to the exercise of so-called biological precautions.

(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; in a figurative meaning – reflection) – a general principle for regulating 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 of the doctrine of R. was made by Prohaska, who proposed 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. doctrine about 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. the structure of the organism and independent of what is happening in the 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, and that, along with the reflex function, there is a sensory function. The weak side of Pflueger’s position was the opposition of R. to the 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 the general scheme of 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. The current state of the study of 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 of organization of neurons in the cerebral cortex, in particular about the reproduction of images of the external world by the system of stellate cells of the eye. analyzer of lower animals. The general theory of the neural organization of reflex centers was proposed by W. McCulloch and V. Pite (1943), who used 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). Assessing the correspondence of the current stimuli and the “nervous model of the stimulus” (E. N. Sokolov, 1959) turned out to be an important factor in the biologically expedient organization of R. Taking into account the mechanisms of self-regulation through feedback, the presence of which was written by Sechenov (1863), the structure of R. in modern cybernetic aspect began to be represented not as an open reflex arc, but as a closed reflex ring (N.A. Bernstein, 1963). Recently, discussions have arisen 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. the principle of neural organization of functional systems of the brain, "DAN USSR", 1964, v. 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.

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

The assumption about the completely reflex nature of the activity of the higher parts of the brain was first developed by the scientist-physiologist I.M. Sechenov. Before him, physiologists and neurologists did not dare to raise the question of the possibility of a physiological analysis of mental processes, which were left to psychology to solve.

Further, the ideas of I.M. Sechenov were developed in the works of I.P. Pavlov, who discovered the ways of objective experimental research of the functions of the cortex, developed a method for developing conditioned reflexes and created the doctrine of higher nervous activity. Pavlov in his works 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 nerve connections formed in the process of 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 doctrine of reflexes has given a lot to understanding the very essence of nervous activity. However, the reflex principle itself could not explain many forms of goal-directed behavior. Currently, the concept of reflex mechanisms has been supplemented by the idea of ​​the role of needs in the organization of behavior; it has become generally accepted 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 influenced by certain needs. These new ideas were expressed in the physiological concepts of the “functional system” by P.K. Anokhin or “physiological activity” by N.A. Bernstein. 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 behavioral plans and implement them in action. The idea of ​​an “acceptor of action”, or a “model of the required future”, allows us to talk about “ahead of reality”.

General mechanism of reflex formation

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

Stimulus - receptor - neuron - effector - response.

In humans, most reflexes are carried out with the participation of at least two neurons - sensitive and motor (motoneuron, 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

Based on a number of characteristics, reflexes can be divided into groups.

1. By type of education: conditioned and unconditioned reflexes.
2. By type of receptor: exteroceptive (skin, visual, auditory, olfactory), interoceptive (from receptors of internal organs) and proprioceptive (from receptors of muscles, tendons, joints)
3. By effector: somatic or motor (skeletal muscle reflexes), for example flexor, extensor, locomotor, statokinetic, etc.; vegetative - digestive, cardiovascular, sweating, pupillary, etc.
4. According to biological significance: defensive, or protective, digestive, sexual, orientation.
5. According to the degree of complexity of the neural organization of reflex arcs, a distinction is made between monosynaptic, the arcs of which consist of afferent and efferent neurons (for example, knee), and polysynaptic, the arcs of which also contain one or more interneurons and have two or more synaptic switches (for example, flexor pain).
6. According to the nature of the influences on the activity of the effector: excitatory - causing and enhancing (facilitating) its activity, inhibitory - weakening and suppressing it (for example, a reflex increase in heart rate by the sympathetic nerve and a decrease in it or cardiac arrest by the vagus nerve).
7. Based on the anatomical location of the central part of the reflex arcs, spinal reflexes and cerebral reflexes are distinguished. Neurons located in the spinal cord are involved in the implementation of spinal reflexes. An example of the simplest spinal reflex is the withdrawal of a hand from a sharp pin. Brain reflexes are carried out with the participation of brain neurons. Among them there 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 brain and spinal cord.

Unconditional

Unconditioned reflexes are hereditarily transmitted (innate) reactions of the body, inherent to 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, unchangeable reactions of the body to certain influences of the external or internal environment, regardless of the conditions for the occurrence and course of reactions. Unconditioned reflexes ensure the body's adaptation to constant environmental conditions. The main types of unconditioned reflexes: food, protective, orientation, sexual.

An example of a defensive reflex is the reflexive withdrawal of the hand from a hot object. Homeostasis is maintained, for example, by a reflex increase in breathing when there is 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 reflex in vertebrates is considered 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. The 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 a neuron of the spinal ganglion is part of the dorsal root of the spinal cord, reaches the motor neuron of the anterior horn and, through a synapse, connects with the body of the neuron or one of its dendrites. The axon of the anterior horn motor neuron is part of the anterior root, then the corresponding motor nerve and ends in a motor plaque in the muscle.

Pure monosynaptic reflexes do not exist. Even the knee reflex, which is a classic example of a monosynaptic reflex, is polysynaptic, since the sensory neuron not only switches to the motor neuron of the extensor muscle, but also sends an axonal collateral that switches to the inhibitory interneuron of the antagonist muscle, the flexor muscle.

Conditional

Conditioned reflexes arise during individual development and the accumulation of new skills. The development of new temporary connections between neurons depends on environmental conditions. Conditioned reflexes are formed on the basis of unconditioned ones with the participation of 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 initiate a reflex response if it is presented for some time together with an unconditioned stimulus. For example, if you give a dog a sniff of meat, then it secretes gastric juice (this is an unconditioned reflex). If you ring a bell at the same time as the meat, the dog’s nervous system associates this sound with food, and gastric juice will be released in response to the bell, even if the meat is not presented. Conditioned reflexes are the basis 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 live successfully in it. As we gain life experience, a system of conditioned reflex connections develops in the cerebral cortex. Such a system is called dynamic stereotype. It underlies many habits and skills. For example, having learned to skate or bicycle, we subsequently no longer think about how we should move so as 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 cell bodies of neurons. 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 are a neurological term that refers to 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 due to the fact that taking a certain substance is associated with a pleasant state (a conditioned reflex is formed that persists for almost the entire life).

Candidate of Biological Sciences Kharlampiy Tiras believes that “the idea of ​​conditioned reflexes that Pavlov worked with is completely based on forced behavior, and this gives incorrect registration [of results in experiments].” “We insist: an object must be studied when it is ready for it. Then we act as observers without violating the animal, and, accordingly, we get more objective results.” What exactly the author means by “violence” of an animal and what the “more objective” results are, the author does not specify.

see also

Notes

1. , With. 320.
2. Pavlov I. Reflex of freedom S. 163.

Swallowing, salivation, rapid breathing due to lack of oxygen - all these are reflexes. There are a huge variety of them. Moreover, they may differ for each individual person and animal. Read more about the concepts of reflex, reflex arc and types of reflexes further in the article.

What are reflexes

This may sound scary, but we do not have one hundred percent control over all our actions or the processes of our body. We are, of course, not talking about decisions to get married or go to university, but about smaller but very important actions. For example, about jerking our hand when accidentally touching a hot surface or trying to hold on to something when we slip. It is in such small reactions that reflexes appear, controlled by the nervous system.

Most of them are inherent in us at birth, others are acquired later. In a sense, we can be compared to a computer, into which, even during assembly, programs are installed in accordance with which it operates. Later, the user will be able to download new programs, add new action algorithms, but the basic settings will remain.

Reflexes are not limited to humans. They are characteristic of all multicellular organisms that have a CNS (central nervous system). Various types of reflexes are carried out constantly. They contribute to the proper functioning of the body, its orientation in space, and help us quickly respond to danger. The absence of any basic reflexes is considered a disorder and can make life much more difficult.

Reflex arc

Reflex reactions occur instantly, sometimes you don’t have time to think about them. But despite all their apparent simplicity, they are extremely complex processes. Even the most basic action in the body involves several parts of the central nervous system.

The irritant acts on the receptors, the signal from them travels along the nerve fibers and goes directly to the brain. There, the impulse is processed and sent to the muscles and organs in the form of a direct instruction to action, for example, “raise your hand,” “blink,” etc. The entire path that the nerve impulse travels is called a reflex arc. In its full version it looks something like this:

• Receptors are nerve endings that perceive a stimulus.
• Afferent neuron - transmits a signal from receptors to the center of the central nervous system.
• The interneuron is a nerve center that is not involved in all types of reflexes.
• Efferent neuron - transmits a signal from the center to the effector.
• An effector is an organ that carries out a reaction.

The number of arc neurons may vary, depending on the complexity of the action. The information processing center can pass through either the brain or the spinal cord. The simplest involuntary reflexes are carried out by the spinal cord. These include changes in the size of the pupil when the lighting changes or withdrawal when pricked with a needle.

What types of reflexes are there?

The most common classification is the division of reflexes into conditioned and unconditioned, depending on how they were formed. But there are other groups, let’s look at them in the table:

Classification sign	Types of reflexes
By nature of education	Conditional Unconditional
According to biological significance	Defensive Approximate Digestive
By type of executive body	Motor (locomotor, flexor, etc.) Vegetative (excretory, cardiovascular, etc.)
By influence on the executive body	Exciting Brake
By type of receptor	Exteroceptive (olfactory, cutaneous, visual, auditory) Proprioceptive (joints, muscles) Interoceptive (endings of internal organs).

Unconditioned reflexes

Congenital reflexes are called unconditioned. They are transmitted genetically and do not change throughout life. Within them, simple and complex types of reflexes are distinguished. They are most often processed in the spinal cord, but in some cases the cerebral cortex, cerebellum, brainstem, or subcortical ganglia may be involved.

A striking example of unconditioned reactions is homeostasis - the process of maintaining the internal environment. It manifests itself in the form of regulation of body temperature, blood clotting during cuts, and increased breathing with increased amounts of carbon dioxide.

Unconditioned reflexes are inherited and are always tied to a specific species. For example, all cats land strictly on their paws; this reaction manifests itself in them already in the first month of life.

Digestive, orientation, sexual, protective - these are simple reflexes. They manifest themselves in the form of swallowing, blinking, sneezing, salivation, etc. Complex unconditioned reflexes manifest themselves in the form of individual forms of behavior, they are called instincts.

Conditioned reflexes

Unconditioned reflexes alone are not enough in the course of life. In the course of our development and acquisition of life experience, conditioned reflexes often arise. They are acquired by each individual individually, are not hereditary and can be lost.

They are formed with the help of the higher parts of the brain on the basis of unconditioned reflexes and arise under certain conditions. For example, if you show an animal food, it will produce saliva. If you show him a signal (lamp light, sound) and repeat it every time food is served, the animal will get used to it. Next time, saliva will begin to be produced when the signal appears, even if the dog does not see the food. Such experiments were first carried out by the scientist Pavlov.

All types of conditioned reflexes are developed in response to certain stimuli and are necessarily reinforced by negative or positive experience. They underlie all our skills and habits. On the basis of conditioned reflexes, we learn to walk, ride a bicycle, and can acquire harmful addictions.

Excitation and inhibition

Each reflex is accompanied by excitation and inhibition. It would seem that these are absolutely opposite actions. The first stimulates the functioning of organs, the other is designed to inhibit it. However, they both simultaneously participate in the implementation of any types of reflexes.

Inhibition does not in any way interfere with the manifestation of the reaction. This nervous process does not affect the main nerve center, but dulls the others. This happens so that the excited impulse reaches strictly for its intended purpose and does not spread to organs that perform the opposite action.

When bending the arm, inhibition controls the extensor muscles; when turning the head to the left, it inhibits the centers responsible for turning to the right. Lack of inhibition would lead to involuntary and ineffective actions that would only get in the way.

Animal reflexes

The unconditioned reflexes of many species are very similar to each other. All animals have a feeling of hunger or the ability to secrete digestive juice at the sight of food; when hearing suspicious sounds, many listen or begin to look around.

But some reactions to stimuli are the same only within a species. For example, hares run away when they see an enemy, while other animals try to hide. Porcupines, equipped with spines, always attack a suspicious creature, a bee stings, and possums pretend to be dead and even imitate the smell of a corpse.

Animals can also acquire conditioned reflexes. Thanks to this, dogs are trained to guard the house and listen to the owner. Birds and rodents easily get used to people feeding them and do not run away at the sight of them. Cows are very dependent on their daily routine. If you disrupt their routine, they produce less milk.

Human reflexes

Like other species, many of our reflexes appear in the first months of life. One of the most important is sucking. With the smell of milk and the touch of the mother's breast or a bottle that imitates it, the baby begins to drink milk from it.

There is also a proboscis reflex - if you touch the baby’s lips with your hand, he sticks them out with a tube. If the baby is placed on his stomach, his head will necessarily turn to the side, and he himself will try to rise. With the Babinski reflex, stroking the baby's feet causes the toes to fan out.

Most of the very first reactions accompany us only for a few months or years. Then they disappear. Among the types of human reflexes that remain with him for life: swallowing, blinking, sneezing, olfactory and other reactions.