What is a reflex definition. Classification of reflexes

Reflexes, or reflex acts, are very diverse. They can be classified into different groups according to a number of characteristics. So, according to them biological significance for the body reflexes divided into food, defensive, sexual, orientation, postural-tonic and locomotor (reflexes of position and movement of the body in space).

Depending on where the receptors are located, the irritation of which is caused by a given reflex act, reflexes are divided into:

• exteroceptive, i.e. caused by irritation of external receptors body surface,
• viscero-, or interoceptive, arising from irritation of receptors internal organs and vessels,
• proprioceptive, caused by irritation of receptors in skeletal muscles, joints, and tendons.

Reflexes They are also classified depending on which parts of the brain are necessary for their implementation. On this basis, reflexes are divided into:

• spinal, in which neurons located in the spinal cord take part,
• bulbar, carried out with the obligatory participation of neurons of the medulla oblongata;
• mesencephalic, carried out with the participation of midbrain neurons;
• diencephalic, in which neurons of the diencephalon participate;
• cortical, in the implementation of which neurons located in the cortex take part cerebral hemispheres brain.

It should be noted that in reflex acts carried out with the participation , located in the higher parts of the central nervous system, neurons located in the lower sections are always involved - in the intermediate, middle, medulla oblongata and spinal cord. On the other hand, with reflexes that are carried out by the spinal or medulla oblongata, midbrain or diencephalon, nerve impulses reach the higher parts of the central nervous system. Thus, this classification of reflex acts is to some extent arbitrary.

Reflexes are also divided according to the nature of the response, depending on which organs are involved in it. So, reflexes are divided into:

• motor, or motor, in which muscles serve as the executive organ;
• secretory, which end with the secretion of glands;
• vasomotor, manifested in the narrowing or expansion of blood vessels.

This classification is acceptable for more or less simple reflexes. With complex reflexes, in which neurons located in the higher parts of the central nervous system participate, as a rule, various executive organs are involved in the implementation of the reflex reaction.

All reflex acts of the whole organism are divided into unconditional And conditional reflexes.

Let us give examples of some relatively simple reflexes, most often studied in laboratory experiments on animals or in the clinic for diseases of the human nervous system.

In a frog, an injection applied to the skin of the paw or immersion of the paw in a weak acid solution causes a reflex contraction of the muscles of this paw - the latter bends and moves away from the irritant. This - flexion reflex.

Applying a piece of filter paper soaked in acid to the skin of the side surface of the frog's body entails contraction of the adductor muscles of the tarsus on the same side, rubbing the irritated area and throwing off the paper. This reflex act is called rubbing reflex.

The dog has skin irritation on his leg electric shock also causes a reflex flexion movement. Rubbing the skin on your side is an irritant scratching reflex: The hind paw of the irritated side is drawn to the side of the body and produces rhythmic flexion scratching movements.

In humans, irritation of the skin of the plantar part of the foot causes reflex flexion of the foot and toes - plantar reflex. In healthy children in the first months of life and in adults with some diseases of the central nervous system, in response to irritation of the sole, the so-called Babinski reflex- extension thumb and fan-shaped divergence of the remaining toes.

Stretching a muscle caused by a short light blow to its tendon causes its reflex contraction - proprioceptive tendon-muscle reflex. This type of reflex includes, in particular, the knee reflex (sharp extension of the leg at the knee when hitting the quadriceps tendon under the kneecap) and the Achilles reflex (sharp contraction of the calf muscle when hitting the Achilles tendon).

Touching the lips of an infant leads to the appearance of rhythmic sucking movements - sucking reflex. Irritation of the back of the throat with any hard object can cause reflex vomiting ( gag reflex). Touching the cornea of ​​the eye leads to the closure of the eyelids - corneal reflex. Illuminating the eye with bright light causes the pupil to constrict - pupillary reflex.

Some of the listed reflexes are spinal, that is, for their implementation, the preservation of the spinal cord is sufficient. These are the reflexes of bending the paw and rubbing the skin on the side, which can be observed in a headless frog. The same are tendon-muscular reflexes (knee, Achilles and others), plantar reflex, urination and defecation reflexes in mammals and humans. They can be observed after transverse section of the spinal cord at the level of the cervical or thoracic segments.

The sucking and corneal reflexes are examples of bulbar reflexes, i.e., reflexes of the medulla oblongata, and the pupillary reflex is an example of a mesencephalic reflex, carried out with the obligatory participation of midbrain neurons.

As we noted above, such a classification of reflexes is conditional: if any reflex can be obtained with the preservation of one or another part of the central nervous system and the destruction of the overlying parts, this does not mean that this reflex is carried out in a normal body only with the participation of this department: in each reflex, all departments of the central nervous system participate to one degree or another.

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 your hand away when accidentally touching 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 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 there are simple and complex species reflexes. They are most often processed in the spinal cord, but in some cases the cerebral cortex, cerebellum, brain stem, or subcortical ganglia may be involved.

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

(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) – 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 mechanically 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 others. natural bodies(“muscular and nervous force” by Haller, “nervous force” by Unzer and Prohaska), and the interpretation of force was materialistic. Creatures contribution to 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. 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 rigorous 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 one. Weak side Pflueger's position was to oppose 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 fore. 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 ones will adapt. 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. Current state teachings about R. Advances in the physiology of the nervous system and close contact between 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 outside world system of stellate cells of the eye. 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.

HIGH NERVOUS ACTIVITY

FUNCTIONS OF THE AUTONOMIC NERVOUS SYSTEM

The autonomic department of 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 realized 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.

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(VND) is the joint activity of the cerebral cortex and subcortical formations, which ensures the adaptation of human behavior to changing conditions external environment.

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, developed during the evolution of a given species, transmitted by inheritance, and 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 usually called conditioned.

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

Reflex arc consists of:

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 connection with this, N.A. Bernstein proposed a new term - a reflex ring, which includes missing link control exercised by the nerve center over the progress of the executive body - 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 the spinal cord as part of the dorsal root, and the processes of motor neurons exit the spinal cord as part of the anterior root. 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 change environment, for example, withdrawing the 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 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.

Reflex. Definition. Types of reflexes. - concept and types. Classification and features of the category "Reflex. Definition. Types of reflexes." 2017, 2018.

Reflex(from Lat. reflexus - reflected) - a stereotypical reaction of a living organism to a certain impact, taking place with the participation of the nervous system. Reflexes exist in multicellular living organisms that have a nervous system.

Classification of reflexes

By type of education: conditional and unconditional

By type of receptor: exteroceptive (cutaneous, visual, auditory, olfactory), interoceptive (from receptors of internal organs) and proprioceptive (from receptors of muscles, tendons, joints)

By effector: somatic, or motor, (skeletal muscle reflexes), for example flexor, extensor, locomotor, statokinetic, etc.; vegetative internal organs - digestive, cardiovascular, excretory, secretory, etc.

According to biological significance: defensive, or protective, digestive, sexual, orienting.

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 1 or more intermediate neurons and have 2 or several synaptic switches (for example, flexor).

According to the nature of the influence 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).

According to the anatomical location of the central part of the reflex arcs distinguish between spinal reflexes and cerebral reflexes. 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.

By type of education Unconditioned reflexes Unconditioned reflexes are hereditarily transmitted (innate) reactions of the body, inherent in the entire species. They perform a protective function, as well as the function of maintaining homeostasis (adaptation to environmental conditions). Unconditioned reflexes are an inherited, unchangeable reaction of the body to external and internal signals, 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. The simplest neural networks, or arcs (according to Sherrington), involved in unconditioned reflexes, are closed in the segmental apparatus of the spinal cord, but can also be closed higher (for example, in the subcortical ganglia or in the cortex). Other parts of the nervous system are also involved in reflexes: the brain stem, cerebellum, and cerebral cortex. The arcs of unconditioned reflexes are formed at the time of birth and remain throughout life. However, they can change under the influence of illness. Many unconditioned reflexes appear only at a certain age; Thus, the grasping reflex characteristic of newborns fades away at the age of 3-4 months. There are monosynaptic (involving the transmission of impulses to the command neuron through one synaptic transmission) and polysynaptic (involving the transmission of impulses through chains of neurons) reflexes.

Conditioned reflexes

Conditioned reflexes arise during individual development and 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 let a dog smell meat, it will secrete 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 underlie 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 a dynamic stereotype. It underlies many habits and skills. For example, having learned to skate or bike, we subsequently no longer think about how we should move so as not to fall.

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 motor neuron of the anterior horn 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 out an axonal collateral that switches to the inhibitory interneuron of the antagonist muscle, the flexor muscle. In humans, the number of reflexes that can be caused in one way or another is quite large, however, in neurological practice, when examining a patient, only a small number of reflexes are examined, the most accessible to identify and characterized by the greatest constancy in people. healthy person.

Reflex Research requires practical skill, in the absence of which a false picture of changes in reflexes can be obtained, and, consequently, an incorrect judgment about the state of one or another part of the nervous system of the subject. When the pyramidal system is damaged, pathological reflexes appear, as well as the so-called. protective reflexes that are not evoked in healthy adults. Decreased (hyporeflexia) or disappearance (areflexia) of reflexes are signs of impaired conductivity or anatomical integrity of the reflex arc in any of its sections. Decreased tendon reflexes are most typical for lesions of the peripheral nervous system. It should be borne in mind that in some healthy individuals reflexes can be evoked only with the help of special techniques, and sometimes even an experienced researcher cannot be evoked. A general decrease in reflexes is observed in deep coma. An increase in tendon reflexes (hyperreflexia) is most often a sign of damage to the pyramidal tracts, however, general hyperreflexia can be observed with intoxication, neuroses, hyperthyroidism and other pathols. states.

An extreme degree of increase in tendon reflexes is manifested by clonus - rhythmic, long-lasting contractions of a muscle that occur after a sharp stretch. The most constant clonus in the pyramidal system is the foot and patella (stretch of the calf muscles and quadriceps femoris). Asymmetry, unevenness (anisoreflexia) of reflexes in combination with pathological reflexes always indicates an organic lesion of the nervous system. Pathological are reflexes that are not evoked in an adult healthy person, but appear only with lesions of the nervous system associated with a decrease in the inhibitory effect of the brain on the segmental apparatus of the spinal cord or the motor nuclei of the cranial nerves.

Pathological reflexes depending on the nature of the motor response, they are divided into flexion and extension (for the limbs) and axial (caused on the head and torso). If we adhere to the order of studying these reflexes from top to bottom, then the main pathological reflexes will be:

• nasolabial reflex(a short blow with a neurol hammer on the back of the nose causes contraction of the orbicularis oris muscle with pulling of the lips forward);
• proboscis reflex(the same motor reaction, but it occurs when a soft blow is applied to the upper or lower lip with a neurological hammer);
• sucking reflex(stroke irritation of the lips with a spatula causes their sucking movements);
• palmomental reflex(stretch irritation of the skin of the palm in the area of ​​the eminence of the thumb causes contraction of the mental muscle on the same side with an upward displacement of the skin of the chin). The appearance of the listed pathological reflexes is characteristic of pseudobulbar palsy, caused by the disconnection of reflex motor centers located in the brain stem with the overlying parts of the central nervous system.

In pathological conditions, carpal tunnel may appear on the hands. pathological reflex Rossolimo: with a short blow with the examiner’s fingers on the tips of the II-V fingers of the patient’s freely hanging hand, flexion (“nodding”) of the terminal phalanx of the thumb occurs. On the feet, the so-called ones are practically important.

Foot pathological reflexes:

• Babinski reflex(extension of the thumb, sometimes with a fan-shaped spread of the remaining fingers, with streak irritation of the skin of the outer edge of the sole);
• Oppenheim reflex(extension of the big toe at the moment of sliding pressure along the crest of the tibia);
• Rossolimo reflex(flexion - “nodding” of the II-V toes with a short blow to the tips of these toes from the side of the sole), etc.

The listed pathological reflexes in adults constitute the syndrome of central, or spastic, paralysis, which develops when the pyramidal system is damaged. In children under 1-1 1/2 years old, these reflexes are not signs of pathology. Symptoms of damage to the pyramidal system include the so-called defensive reflexes. Protective (shortening) reflexes occur most often with transverse damage to the spinal cord and can serve as additional signs in determining the level of its damage. The easiest way to cause these R. is an injection (sometimes a series of repeated injections) into the sole, which causes involuntary flexion of the paralyzed leg at the hip, knee, and ankle joints, and the leg seems to be pulled back (“shortened”). Protective R. can cause persistent flexion contracture of the legs when, in addition to damage to the spinal cord, there is irritation of the dorsal roots (tumor, tuberculous spondylitis, etc.). To judge the degree of violations of various structures of the nervous system during the topical diagnosis of its lesions, a study of some autonomic reflexes- vasomotor, pilomotor, sweating, visceral, etc. To study these reflexes, special methods of applying irritation and recording responses, various pharmacological tests are used to judge the state of the autonomic nervous system. When examining a patient, a study of vasomotor reactions of the skin caused by its line irritation in various areas bodies.

Pilomotor reflex(contraction of the muscles that raise the hair, with the appearance of the so-called goose bumps) is caused by cooling or pinching the skin in the area of ​​the shoulder girdle; the response normally occurs on the entire half of the body (on the side of irritation); damage to the autonomic centers in the spinal cord and nodes of the sympathetic trunk leads to the absence of a reflex in the corresponding innervation zone. A similar picture is obtained under pathological conditions when the sweating reflex is impaired. The most accessible for research are visceral reflexes, allowing to identify the excitability of certain parts of the autonomic nervous system - ocular reflex(slowing of the pulse in response to gentle pressure on the eyeball), orthostatic reflex(heart rate acceleration when moving from a lying position to an upright position), clinostatic reflex(pulse slows down after returning to a horizontal position). With normal excitability of the autonomic nervous system, the difference in pulse rate should not exceed 8-12 beats per minute.

Examples distant reflexes can serve pupillary reflex to light, which has great diagnostic value, as well as start reflex, an increase in which is manifested by a sharp shudder of the body at any unexpected sound or flash of light. Patients whose start reflex is impaired due to damage to certain parts of the brain cannot quickly engage in activities that require a quick reaction and motor mobilization. When the start reflex is preserved, movements that require its participation are often performed better than other movements that do not require action on a sudden signal and are difficult due to general muscle stiffness.