From Big Medical Encyclopedia

BRAKING — the active reaction of this or that system of cells of an organism arising in the course of excitement and leading to suppression of its specific activity.

History. For the first time phenomenon of T. it was opened in 1845 by brothers E. E. F. W. Weber and E. F. W. Weber who found delay of rhythmic action of the heart at irritation of the peripheral end of a vagus nerve (so-called vagal braking). Existence of T. in activity of c. it was noted by N of page L. Trau-be (1847), to-ry observed a stop of respiratory movements (i.e. braking of periodic activity of a respiratory center) at irritation of the central end of a vagus nerve. Definition of a role of T. as basic fiziol. the process lying along with excitement (see) at the heart of integrative activity of a nervous system belongs to I. M. Sechenov (see Setschenow's inhibition). Pilot studies of the nature and value T. H were carried out. E. Vvedensky, Ch. Sherrington, A. F. Samoylov, M., A. Kiselyov, I. P. Pavlov, etc. I. P. Pavlov formulated idea of T. in higher nervous activity (see), having allocated external (unconditional) and internal (conditional)

T. O mechanisms T. numerous, quite often contradictory assumptions expressed. Only after development by J. Ekkls and sotr. (1951) a method of intracellular microelectrode assignment of electric potentials from an outer membrane of a nervous cell became possible directly to register the changes in its superficial membrane arising during T., and experimentally to analyze the reasons causing suppression of excitement.

On the basis of the received results several types T were allocated., having various cellular origins.

It is proved also that T. develops in the fields of synoptic connection between nervous or nervous and effector cells and has no (unlike excitement) ability to further active distribution.

Types and braking mechanisms.

The most widespread is postsynaptic the T., resulting from specific changes of a postsynaptic membrane of the corresponding synapse (see). It is characterized by short-term hyperpolarization of the postsynaptic membrane called brake posts inaptichesk by it the potential (TPSG1). At synchronous receipt of action potentials to the synoptic terminations TPSP on a tormozimy cell differs in the short accruing phase (apprx.

1,5 ms) and the subsequent recession by duration apprx. 3 ms. At more difficult braking impacts on motor-neurons which are carried out through the policy inaptichesk not ways, TPSP has much less correct and longer current that is connected with receipt of a disperse impulsation from interneuronels and uneven summation of TPSP caused by each presynaptic impulse. In case exciting synoptic action matches development of TPSP, as a result of algebraic summation of opposite changes of potential of a membrane efficiency of synaptic activation is weakened, as leads to braking of cellular activity (see. Nervous cell). It, however, is not the only reason postsynaptic T., as increase in conductivity of a postsynaptic membrane to certain ions and the corresponding decrease in its resistance is the cornerstone of development of TPSP that also leads to reduction of size of the exciting depolarizing action. Emergence of hyperpolarization of a postsynaptic membrane at T. it is connected with action on it certain brake mediators (see Mediators). For motor-neurons of a spinal cord such mediator is amino acid glycine, and his specific antagonists — strychnine and tetanic toksinony Direct leading of glycine to a surface of motor-neurons (e.g., by means of a mikroionofo-cut) causes the same changes of polarization and conductivity in their membrane, as well as natural T. For nervous cells of other type a mediator posts inaptichesk oho T. piperidic acid (GAMK) serves, antagonists a cut are picrotoxin and bikukkulin. As each nervous cell in connection with features of the metabolism can synthesize and emit mediator substance of a certain type (the so-called principle of Dale), for transformation of the exciting action characteristic of the synoptic terminations of afferent fibers, in braking inclusion in the appropriate nervous way of an additional inhibitory neuron capable to synthesize and emit glycine or GAMK is necessary. Existence of such neurons was proved by means of micro electrode researches (see. Microelectrode method of a research). They represent the korotkoaksonny nervous cells located in close proximity to the neuron which is exposed postsynaptic to T.

The reasons of a giperpolyarizatspa of a membrane at action of a brake mediator were studied by means of registration of changes of TPSG1 against the background of experimental shift of membrane potential of a brake cell, and also change of transmembrane gradients of various ions (by their injection through an intracellular microelectrode). It is shown that dependence between TPSP and level of membrane potential has linear character. However at achievement of 80 mV change of hyperpolarization with depolarization happens the membrane potential of size of an order —. It indicates a possibility of increase in permeability of a postsynaptic membrane for potassium ions (equilibrium potential apprx. — 90 mV) and ions of chlorine (equilibrium potential apprx. — Yuma) under the influence of the braking mediator. Mikroponofo-retichesky introduction of ions of chlorine in a brake kletkp also turns hyper weeding rizatsnonny TPSG1 in a dipole rizatsionny that corresponds to the assumption of increase in permeability of a membrane for ions of chlorine at postsynaptic T. Experiences with electrophoretic leading in neurons of various anions allowed to draw a conclusion that ions, the hydrated radius to-rykh does not exceed 1,6 ionic radiuses of potassium, give the same effect, as well as ions of chlorine. It was suggested that in a postsynaptic membrane prp action of the braking mediator the ion channels of a certain diameter passing in fiziol open. conditions ions of chlorine, the movement to-rykh inside cell are created by the transmembrane current which is hyper polarizing gtosts inapt ichesk at yu a membrane. Along with activation of anion channels there can be an activation and the cationic channels creating transmembrane current of potassium ions.

TPSP are registered in neurons of all departments of the central nervous system, including in a cerebral cortex (see). In peripheral neuro and effector connections poyetei-naptichesky T. it is revealed in muscles at backboneless animals, in a myocardium and smooth muscles at vertebrata. In neuromuscular connections at invertebrates the braking mediator is GAMK, in a myocardium — acetylcholine. Acetylcholine (see) mediates the postsynaptic braking action also in certain synoptic connections of a nervous system at

mollusks though in other synapses it is an exciting mediator. The same double function in nek-ry synapses is carried out by serotonin (see). The dual nature of action of the same mediator in synapses of different type indicates that the exciting or braking final effect decides not by chemical structure of a mediator, but specifics of its interaction on a certain type of receptors of postsynaptic membranes.

The T is less widespread presynaptic. It is most expressed in synoptic connections of primary afferent neurons and the central neurons of the second order. Presynaptic T. develops in a presynaptic part of a synapse (the synoptic terminations) and it is created due to interaction of the terminations akso-aksonal-nykh synapses (see) therefore there is a suppression of exciting action of the nervous impulses arriving on presynaptic ways to a postsynaptic cell. Existence of akso-axonal synapses was proved by means of electronic microscopic examinations of various brain structures (see the Synapse). Intracellular recording of potentials, elektrotonichesk of these fibers spreading to an extra brain part from their intracerebral part, showed that in time a press inapt ichesk oho T. the long depolarization of the central bombways of these fibers leading to reduction of quantity of the mediator allocated terminalyam in response to the nervous impulse arriving to them, and respectively to weakening of their exciting (depolarizing) action for a postsynaptic membrane develops. The reasons of reduction of allocation of a mediator are definitely not established; it can be connected with reduction of amplitude of action potential at its receipt in the depolarized terminations, disturbance elektrosekretor-ache the communication which is the cornerstone of process of allocation of a mediator nerve terminations, etc. Changes similar presynaptic T., T can be caused by the DIN direct appendix K to terminalyam afferent fibers, and itself. it can be weakened by effect of picrotoxin. Assume that a mediator of the akso-axonal synapses causing presynaptic T., DIN is To; at nek-ry backboneless animal (mollusks) it is revealed presynaptic T., connected with release of serotonin.

At microelectrode researches it was established that for development presynaptic T., as well as at postsynaptic T., excitement of the internuncial neurons forming an akso-axon-lnye synapses with the tormozimy synoptic terminations is necessary. Increase in maintenance of potassium ions in the intercellular environment surrounding presi-nagkhtichesky bombways also has similar effect on synoptic transfer. Assume also that increase in extracellular ion concentration of potassium is the main reason pre-sinaitichesky T.

Patol. disturbances of mechanisms of formation of T. are observed in a sharp form at poisoning of an organism with the toxins which are specifically suppressing these or those its forms (strychnine, a tetanin, picrotoxin)! As the most general manifestation of such disturbance serves development in response to external irritations of the convulsive attacks which are followed by an ataxia, sensitivity and functions of a number of internals.

Braking in higher nervous activity — an ego different complex of the brake processes interfaced with exciting interaction to-rykh provides the analysis of the factors operating on an organism and the organization of adaptive behavior for preservation of homeostatic balance of an organism with the environment. The leading role at the same time belongs central to T., though in the general analitiko-integrative activity of a brain also processes of peripheral braking, i.e. braking participate in peripheral parts of the nervous system (e.g., lateral T., developing in receptive fields around a zone of excitement and providing contrast of perception). The central braking, according to I. M. Sechenov, is an indispensable condition for formation of feelings, representations, accumulation of touch impressions, a basis of the device of memory, all forms of thinking as the way of processing and comparison of everything imprinted in a brain and the organization of adaptive behavior of an organism (see Setschenow's inhibition).

I. M. Sechenov in an experiment found also oppressing action of superstrong irritation of the touch terminations of a thalamus on the reflex centers of a spinal cord. In the subsequent the similar effect was observed at superstrong stimulation and other formations of c. N of page. Braking such in relation to higher nervous activity (see) I. P. Pavlov called ultraboundary, guarding, believing that it is connected with functional exhaustion of nervous cells and protects them from irreversible loss of working capacity. Big contribution to studying of a problem central T. brought H. E. Vvedensky, Ch. Sherrington,

A. A. Ukhtomsky, P. K. Anokhin, I. S. Beritashvili, E. A. Asratyan, etc. H. E. Vvedensky in model experiences with irritation of nerve-muscle preparation found out that at a certain increase in frequency of an impulsation the exciting effect is replaced by brake. It created the general theory of braking — the theory of a parabiosis (see), according to a cut, braking is considered as not extending - sya the congestive excitement (see) arising at change of a functional condition of the site of nervous tissue which is characterized by decrease in its functional mobility — lability (see). Having assumed as a basis the provision that development of a parabiosis takes place a number of phases (leveling, paradoxical, brake), I. P. Pavlov used these representations in the analysis of phases of a dream, considering it as a special type of internal inhibition — a diffuse brake condition of bark and other departments of a brain (see the Dream).

Logically developing the doctrine H. E. Vvedensky, A. A. Ukhtomsky formulated and proved the principle of a dominant (see) playing a large role in coordination of activity of nerve centers. To them it was shown that at rather strong excitement of a certain modality of any nerve center it becomes dominating, dominating, strengthening the excitement at the expense of T. activity of other centers. Reflex reactions, inherent for them, at the same time iye are shown. Strengthening of excitement of the dominant center can transfer it to a state parabiotnchesky T. Printsip of a dominant is important for understanding fiziol. the mechanisms which are the cornerstone of attention.

Essential value for coordination of reflex activity has central T., interfaced to excitement. II. And. Spiro in 1874 on spinal drug of a frog found out that bending of a pad at irritation of the site of skin on one party is followed by extension of a pad on the opposite side, i.e. the reciprocal relations (see Retsi-proknost). Existence interfaced by T. at stimulation of a motive zone of a cerebral cortex H was described in 1897. E. Vvedensky. The reciprocal relations at the level of a spinal cord were studied by Ch. Sherrington (1898) in detail. On the basis of reciprocal relationship of I. S. Beritashvili (1915) explained also so-called the general to T., arising at excitement of certain touch systems or muscular groups, interfering manifestation of any other reflex acts and by that providing selective activity of necessary working bodies against the background of T. others. A look interfaced by T., according to Maunt-kasl (V. Century of Mountcastle, 1964), is also afferent T., arising around the excited zone in network of projective neurons and participating in specification of provision of the irritated point on a receptor surface.

It is known what great value I. M. Sechenov gave to process of T. in formation of feelings, representations, the ideas, in processes of memory and thinking. I. P. Pavlov considered a question of studying of mechanisms T. cardinal for understanding of all work of a brain. He emphasized that process of T. performs not only guarding and coordination functions, but provides all variety of brain activity and first of all implementation of the principle of systemacity, a dynamic stereotype as sign of perfection of work of a brain. At the same time systemacity, a dynamic stereotype was understood as the mosaicity of exciting and brake processes allowing an organism by transition from excitement to braking (and vice versa) quickly to adapt to continuously changing living conditions.

Different types of braking in century and. supporters of the Pavlovsk school divided into two basic groups: the first — different types unconditional T. as specific, inborn, not demanding special development (earlier it was called external since the positive conditioned reflex at action of an external foreign irritant oppresses); the second — different types conditional T., individually developed, it is called vnu-chatter of N by it as waves hiccups without in me 111 and those l e t in a 11< >with t about r about ii it r and z d r and-zhptelya. In unconditional T. allocated T. negative induction, as foreign external irritant. creating the strong center of excitement in a cerebral cortex. induces to those T. the center of a conditioned reflex, also zairedet noo (guarding) T.

Among types conditional T. distinguished p ugasatelny, differentsiro-vochny (its version the conditional brake is), zapazdyva-telyiy and close to it — trace. And. II. Pavlov constantly emphasized that the nature conditional T., its ratio with exciting process remain not clear and called it «a damned question of physiology». Development elektrofiziol. researches allowed to show that anything of T. there is a result of different interaction of vozbuzhdeniye, a net result to-rogo is defined by the nature of synoptic and system bonds. Elektroentsefalografichesky researches, in particular, showed that all types conditional T. are connected with initial excitement of various departments of a brain and with activation integrativno of the analyzing system. Main type conditional T. the T is ugasatelny., that P. Pavlova about obligatory oppression of a nervous cell at repetition of monotonous stimulation will be coordinated with representation And, if it is supported with nothing. The analysis of pulse activity of neurons and rhythmics of neural networks shows that repetition of an incentive without reinforcement gradually reduces process of activation, transferring it to brake. The supporting excitement (food, pain stimulation, etc.) possesses rastormazhivayushchy action as the flow of nervous impulses from external and internal receptors, and also from pronriotseptor of muscles at motive answers as if «washes away» collected T. At differentiation (i.e. distinguishing of two irritants) one of irritants is constantly supported that prevents accumulation of brake factors; another repeats without reinforcement that leads to development ugasatelny T. and the irritant becomes effectless. Zagkhazdyvatelny and trace T. differ in the fact that the reinforcement arrives not at once, and later a nek-swarm time. The difference is only that at delay the prearranged signal proceeds at action of a reinforcement, and at a trace conditioned reflex the reinforcement is separated from a signal by a pause of this or that duration. Therefore, in both cases a certain timepoint is supported (against the background of the operating signal or after its switching off). At the same time excitement (in the form of activation of a brain) arises at the time of inclusion of a prearranged signal; then it is braked (effectors are slowed also down at this time) and again arises shortly before the moment of a reinforcement when it passes also to executive bodies therefore the conditioned reflex is implemented (see).

In human life and animals processes of T. play an exclusive role. In addition to continuous coordination, approval of all current departures of an organism — its muscle performance, work of touch systems, various internals, different departments of the most nervous system, T. provides the organization of all behavior. It is proved that it is achievement of evolutionary process. Conditional T. allows to differentiate the mass of irritants that is the cornerstone of training. All social relations, standards of behavior, morals are based on education of restraint, ability to manage the feelings, i.e. on ability to manage excitement by means of T. The natural ratio of force of exciting and brake processes defines types of higher nervous activity (see).

Various diseases, heavy experiences, overstrain of a nervous system often lead to failure of T., what is the cornerstone of many nervous N of mental diseases. I. P. Pavlov at excitable animals and people connected development of a neurasthenia owing to «sshibka» of nervous processes of an opposite sign with weakening of brake process (see Neurosises experimental). Various degree diffuse cortical T. (with passive distribution and on subcrustal structures) I. P. Pavlov explained nek-ry forms of senile dementia, neurosises and schizophrenia. In particular, such phenomena as an echolalia, an ekhopraksiya (see. A catatonic syndrome), a stereotypy (see Schizophrenia.), he considered symptoms of various phases of a hypnotic state.

Complexity of studying of dynamics of process of T. is that an indicator of T. in a nervous system lack of external reaction — muscular contraction, salivation, etc. is (zero result of action of an irritant). Therefore about T. it is possible to judge by weakening of effector reaction or by indirect indicators, napr, by an after-effect on process of excitement. Only elektrofiziol. techniques (registration of the electroencephalogram, pulse and slow activity) allowed to observe the course of nervous processes directly in nervous tissue and to monitor their development, comparing with a net result of action of irritants. At researches of century and. of the person use also registration of motor and verbal reactions, a skin and galvanic reflex, various vegetative indicators — changes of breath, the electrocardiogram, vascular reactions, etc.

Bibliography: Anokhin P. K. Biology and neurophysiology of a conditioned reflex, M., 1968; Vvedensky H. E. Complete works, t. 4, JI., 1935; To about with t yu to P. G. Fiziologiya of the central nervous system, Kiev, 1971; To r ft-t of N of Yu. G. Analysis of signals brain, in L., 1977; Pavlov I. P. Twenty years' experience of objective studying of higher nervous activity of animals, Half-N of SOBR. soch., t. 3, book 2, M. — L., 1951; Sechenov I. M. Chosen works, t. 1, page 7, M., 1952; Ukhtomsky A. A. Collected works, t. 1, page 232, L., 1950; Private physiology of a nervous system, under the editorship of P. G. Co-styuka, etc., L., 1983; Sh e r r and N of g -

t about N of H. Integrative activity of a nervous system, the lane with English, L., 1969; E to l with D. Physiology of synapses, the lane with English, M., 1966; it, Brake ways of the central nervous system, the lane with English, M., 1971.

P. G. Kostiuk; Yu. G. Kratin (braking in higher nervous activity).