RECEPTORS

From Big Medical Encyclopedia

RECEPTORS (Latin receptor accepting) — the specialized sensitive educations adapted for perception of incentives (irritants), adequate for an organism.

In scientific literature use also the concept «touch receptors» for designation P., providing sensitivity (see) an organism. Thereby scopes of the term «receptors» (in physiology) and the term «biochemical receptors» (used in pharmacology, biochemistry, immunology, etc. for designation of the supermolecular structures of a cell providing interaction with chemical substances — mediators, hormones, etc., and the corresponding reactions of a cell) are differentiated.

Touch receptors

In rather just organized sensitive structures (e.g., in internals, in structures of a musculoskeletal system, in skin) the concept «receptors» matches the concepts «receptor devices», «touch bodies». In more difficult sensitive educations (e.g., in acoustic organs and sight, a vestibular labyrinth, etc.) R. are only a part of touch body (see. Vestibular analyzer , Taste , Sight , Touch , Hearing ). In R. energy of an irritant is transformed to specific activity of a nervous system, to the signals bearing on afferent conductors to nerve centers information on characteristics of the acting agent. During R.'s evolution became complicated and specialized since the quicker and more stoutly the organism is capable to obtain information on a state and on changes of surrounding and internal environment, the chances of an organism to survive in continuous fight for existence are higher.

High-organized animals have a big variety of R. allowing them to perceive very precisely irritants of the most different types (modalities): mechanical, chemical, temperature, light, electric. Depending on it distinguish mechanioreceptors (see), chemoceptors (see), thermoreceptors (see), photoreceptors (see); sometimes speak about existence of nociceptors, i.e. the receptors perceiving painful irritants (see. Pain ).

Nek-ry receptors are adapted for perception of one type of irritation (monomodal R.), others — for perception of several types of irritants (polymodal R.). Historically R.'s division into the so-called distantny R. serving for obtaining information on nek-rum distance from a source of irritation and the contact R. perceiving an incentive at direct contact with it remained. The ground mass of R., especially highly specialized, perceives irritants from environments. These are so-called exteroceptors (see. Exteroception ). An important role is played by R. signaling about irritants of internal environment i.e. interoceptors (see. Interoception ). Often distinguish R. from them of a musculoskeletal system — proprioceptors (see).

Depending on reaction on the operating stationary influence of R. is long divide on quickly and slowly adaptive (phase and tonic R.). On structural and functional features of R. the feeling Rubles are subdivided on initially feeling and for the second time. Perception of an incentive in initially feeling R. is carried out directly (i.e. initially) by the terminations of a sensory neuron (see. Nerve terminations ). At for the second time the feeling R. between the operating incentive and a sensory neuron the specialized cell is located, from a cut at irritation it is allocated mediator (see), acting already directly on the terminations of a sensory neuron. Thus, R. of this type have an external irritation on a sensory neuron indirectly, for the second time. Neuromuscular spindles, neurotendinous spindles, and to for the second time feeling — receptors of acoustic organs, sight, taste, a vestibular labyrinth, etc. belong to initially feeling R. at vertebrate animals, e.g.

In R. allocate three main parts: auxiliary structures, napr, the capsule at the encapsulated fabric R. (like Pachini's little bodies, Meyssner, etc.), the sound carrying out structures of an acoustic organ, etc., actually retseptiruyushchy elements containing the perceiving substrate, and system of generation of local electric potentials (so-called receptor, or generating, potentials). At initially feeling R. answers arise in the termination of a sensory neuron, and at for the second time the feeling R. — in a retseptiruyushchy cell. If local electric potential has the depolarizing effect on electroexcitable structures of the terminations of a sensory neuron, then there is a generation of impulses (see. Nervous impulse ), bringing to c. N of page information on the events proceeding in R.; from here and term «generator potential».

Between power of irritation, adequate for R., and frequency of an impulsation (on average the range of loadings) there is a logarithmic dependence that corresponds to Weber's law — Fekhnera (see. Feeling ), Amplitude of receptor potential, despite constancy of an irritant, can flyuktuirovat. This fact, and also fluctuation of excitability of the structures generating impulses define the general fluctuation of excitability of R. in time that is the cornerstone of so-called functional mobility R.

Odna from the most important characteristics of R. their high sensitivity to action of an adequate irritant is. R.'s sensitivity is estimated by the size of an absolute threshold, i.e. the minimum power of irritation capable to cause R.'s excitement (see. Excitement ). Absolute thresholds of the high-differentiated R. (in organs of sight, hearing, sense of smell) can be extremely low, approaching theoretically limiting values.

R.'s activity is under neurohumoral control. Humoral factors are capable to change excitability of River to a certain extent. Efferent nervous influences can change thresholds of reaction, cause both excitement, and R. U braking of vertebrate animals efferent influences on the feeling R. highly sensitive for the second time have preferential oppressing character, and on less sensitive initially feeling — generally facilitating (or exciting) character.

R.'s pathology is various. As the reason any disturbances can serve in auxiliary structures of R. (e.g., in photoconductive structures of organs of sight, the sound carrying out structures of hearing), in actually touch elements (e.g., at an atrophy of an olfactory epithelium, at disturbances of biochemical transformations of rhodopsins, etc.) and, at last, in afferent nervous conductors (e.g., at injuries and diseases of nerves). If patol. changes of auxiliary structures of R. can be exposed to treatment (e.g., at cataracts, otoscleroses), that damage of actually retseptiruyushchy elements (photoreceptors, voloskovy receptors etc.) usually leads to irreversible changes in activity of touch bodies.

Methods of a research P. are various; morphological (sacred and electronic and microscopic), physiological (various microelectrophysiologic, psychophysiological, etc.), pharmacological, biochemical, biophysical, mathematical and other methods apply many.

Cellular receptors

In a metaphyte the information transfer between cells happening to participation of hormones, neurotransmitters (mediators), neuropeptids and other biologically active agents includes a stage of interaction of molecules of these substances (they are called also ligands) with the relevant supermolecular structures, or cellular receptors. They can be located as in a cell (e.g., cellular R. to the steroid hormones which are easily getting in a cell thanks to their solubility in lipids of a cellular membrane), and on a surface of a cellular membrane (cellular R. to proteins, peptides, neurotransmitters). Both intracellular, and membrane cellular R. support the center of binding providing specific linkng of a ligand with cellular Rubles. After binding, e.g., of a molecule of steroid hormone with cytoplasmatic R. and formations of a complex hormone — cellular R. this complex gets in a cellular kernel where contacts the corresponding acceptor after what the molecule of hormone separates from a complex and leaves in cytoplasm, at the same time the genetic device is at the same time activated cells (see). The final result of this activation is sharp strengthening of synthesis of a number of specific and nonspecific proteins of a cell that represents the response of a target cell to effect of hormone.

The processes happening at linkng of a molecule of a ligand with the cellular R. localized on a cellular membrane (see. Membranes biological ), consist of a number of the stages proceeding with high speed. The change of properties of the phospholipidic matrix surrounding cellular R. happening at the same time provides signal transmission from the center of binding of a ligand (through a number of intermediate links) on adenylate-tsiklazny the center and its activation. Cyclic AMF (see. Adenosine - phosphoric acids ) is the peculiar second intracellular carrier of information defining the response of a cell to action of a ligand. Thus, there is an activation of the corresponding protein kinases, change of permeability of a cellular membrane for a number of ions, strengthening of an expression of genetic information. Important opening was detection in c. N of page of cellular R. to a number of neyronalny peptides, napr, to groups of the peptides called endorphines and enkephalins and also cellular R. to many psychotropic medicines (to Imipraminum, a haloperidol, diazepam, etc.). Interaction of the ligands stated above with cellular R. changes ability of nervous cells to answer operation of neurotransmitters, i.e. has the modulating effect on their activity. E.g., linkng of drugs of a benzodiazepine row with benzodiazepine cellular R. strengthens the response of GAMK-ergichesky neurons to action piperidic to - you are (GAMK), influencing at the same time binding of GAMK by the corresponding cellular R. Due to the detection in c. the N of page of the endogenous ligands competing with morphine for places of binding and possessing morfinopodobny action is carried out search of endogenous connections like endogenous diazepam, an endogenous haloperidol, etc. that can be in case of their detection of great importance for a wedge, practicians.

Disturbances of mechanisms of reception play an important role in development of a number of diseases of the person, napr, nek-ry types of a diabetes mellitus, a giperkholi-sterinemiya, etc. Along with R.'s types considered above on a surface In - and T lymphocytes the membrane cellular R. playing an important role in work of immune system and also cellular R. to a number of viruses are revealed.



Bibliography: Glebov R. I. and Kryzhanovsky G. N. Functional biochemistry of synapses, M., 1978; Granite P. An electrophysiologic research of reception, the lane with English, M., 1957; Rosen V. B. and Smirnov A. N. Receptors and steroid hormones, M., 1981, bibliogr.; Tamar G. Fundamentals of touch physiology, the lane with English, M., 1976; Physiology of touch systems, under the editorship of A.S. Batuyev, page 34, L., 1976; Cell membrane receptors for drugs and hormones, multidisciplinary approach, ed. by R. W. Straub a. L. Bolis, N. Y., 1978; Cell! membrane receptors for viruses, antigens, and antibodies, polypeptide hormones, and small molecules, ed. by R. F. Beers a. E. G. Bassett, N. Y., 1976; The receptors, comprehensive treatise, ed. by R. D. O’Brien, v. 1, N. Y. — L., 1979.


O. B. Ilyinsky; P. P. Lidemang (cellular receptors).

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