receptor

Physiol a sensory nerve ending that changes specific stimuli into nerve impulses

Receptor

a sensory nerve structure that perceives and transforms stimuli from an organism’s external or internal environment and transmits information about the agent of the stimulus to the nervous system. Receptors vary in structure and function. They may be free nerve endings, endings covered with a special capsule, or specialized cells in such complex structures as the retina or Corti’s organ, which consist of many receptors.

Receptors may be external—exteroceptors—or internal—interoceptors. Exteroceptors are located on the external surface of the body of an animal or man, where they receive such stimuli from the external world as light, sound, and heat. Interoceptors are found in such tissues and internal organs as the heart, lymphatics, blood vessels, and lungs. They receive stimuli that give information about the condition of internal organs (visceroceptors) and the position of the body or part of it in space (vestibuloceptors). The proprioceptors, a type of interoceptor, are located in muscles, tendons, and ligaments. They transmit information about the static condition and dynamics of the muscles.

Mechanoreceptors, photoreceptors, chemoreceptors, and thermoreceptors respond to different types of stimuli. Dolphins, bats, and moths have receptors sensitive to ultrasound. The receptors of some fishes are sensitive to electric fields. The question of the existence of receptors sensitive to magnetic fields in certain birds and fishes awaits further study.

Monomodal receptors respond to stimuli of only one kind, either mechanical, photic, or chemical. They include receptors differing in level of sensitivity and reaction to stimuli. For example, the photoreceptors of vertebrates are subdivided into the more sensitive rod cells, which function as receptors of twilight vision, and the less sensitive cone cells, which enable man and some animals to see in the daylight and to perceive different colors. The mechanoreceptors of the skin are subdivided into the more sensitive phase receptors, which react only to the dynamic phase of deformation, and static receptors, which also react to constant deformation. Such specialization permits detection of the most significant properties of a stimulus and refined analysis of the stimuli received.

Multimodal receptors react to stimuli of more than one kind, such as chemical and mechanical or mechanical and temperature. The specific information coded in the molecules is transmitted to the central nervous system along the same nerve fibers in the form of impulses, which during their course receive repeated energy reinforcement.

The historic distinction between distance receptors (visual, auditory, and olfactory), which receive signals from a source of stimulation some distance away from the organism, and contact receptors, those that come into direct contact with a source of stimulation, is still retained. A distinction is also made between primary and secondary receptors. In primary receptors, the substrate that reacts to an external influence is embedded in the sensory neuron itself, which is directly (primarily) excited by the stimulus. In secondary receptors, additional specialized (receptive) cells are situated between the acting agent and the sensory neuron. The energy of external stimuli is transformed into nerve impulses in these cells.

All receptors have a number of properties in common. They are specialized to receive certain types of stimuli. During the action of a stimulus, a change occurs in the variation of the bioelectric potential on the cell membrane. This process, called receptor potential, either generates rhythmic impulses in the receptor cell directly or causes them to appear in another neuron, connected to the receptor by a synapse. The frequency of impulses increases with increasing intensity of stimulation. If stimulation is prolonged, the frequency of impulses in the fiber branching from the receptor decreases. This reaction, called physiological adaptation, varies in duration from receptor to receptor.

The high sensitivity of receptors to adequate stimulation is measured by the absolute threshold or minimum intensity of stimulation capable of exciting the receptors. Thus, five to seven quanta of light striking the eye’s receptors cause a sensation of light, whereas a single quantum is sufficient to excite an individual photoreceptor. Receptors may also be excited by inadequate stimulation: an electric current can cause a sensation of light or sound by acting on the eye or ear. Sensations are related to the specific sensitivity of receptors that came into being during the evolution of organic nature. Vivid perception of the world is caused chiefly by information coming from the exteroceptors. Information from the interoceptors does not produce distinct sensations.

The functions of the various receptors are interrelated. The interaction of vestibular receptors and of the cutaneous receptors and proprioceptors with the visual receptors is effected by the central nervous system. This interaction causes perception of the size and shape of objects and their position in space. Receptors may also interact among themselves without the involvement of the central nervous system by virtue of their direct contact with one another. Such interaction among visual, tactile, and other receptors is an essential element in the mechanism of spatial and temporal contrast.

Receptors are controlled by the central nervous system, which adjusts them according to the needs of the organism. These adjustments, whose mechanism has been insufficiently studied, are effected by means of special efferent fibers located close to some receptor structures.

Receptor functions are investigated by recording bioelectric potentials directly from receptors or associated nerve fibers and also by recording the reflexes elicited by stimulating receptors.

REFERENCES

Granit, R. Electrofiziologicheskoe issledovanie retseptsii. Moscow, 1957. (Translated from English.)
Prosser, L., and F. Brown. Sravnitel’naiafiziologiia zhivotnykh. Moscow, 1967. (Translated from English.)
Vinnikov, Ia. A. Tsitologicheskie i molekuliarnye osnovy retseptsii: Evoliutsiia organov chuvstv. Leningrad, 1971.
Fiziologiia cheloveka. Edited by E. B. Babskii. Moscow, 1972. Pages 436–98.
Fiziologiia sensornykh sistem, parts 1–2. (Rukovodstvopo fiziologii.) Leningrad, 1971–72.
Handbook of Sensory Physiology, vol. 1, part 1; vol. 4, parts 1–2, Berlin-Heidelberg-New York, 1971–72.
Melzack, R. The Puzzle of Pain. Harmondsworth, 1973.

A. I. ESAKOV

Pharmacologic receptors (also cell or tissue receptors). Pharmacologic receptors are situated on the membrane of effector cells. They receive regulatory and trigger signals from the nervous and endocrine systems and are exposed to many pharmacologic agents that selectively act on such cells. The receptors transform this action into the cell’s specific biochemical or physiological reactions. The pharmacologic receptors that carry out the activity of the nervous system are the ones that have been studied in greatest detail.

Two types of pharmacologic receptors transmit the influence of the parasympathetic and motor divisions of the nervous system (through the mediator acetylcholine): The N-cholinergic receptors transmit nerve impulses to the skeletal muscles and from neuron to neuron within the nerve ganglia, while the M-cholinergic receptors help regulate cardiac activity and the tone of smooth muscles. The influence of the sympathetic nervous system (through the mediator norepinephrine) and of the hormone secreted by the adrenal medulla (epinephrine) is transmitted by the α- and β-adrenergic receptors. Stimulation of the α-adrenergic receptors constricts blood vessels, raises blood pressure, dilates the pupils, and causes some smooth muscles to contract. Stimulation of the β-adrenergic receptors raises blood sugar levels, activates enzymes, dilates blood vessels, causes smooth muscles to relax, and increases the frequency and intensity of cardiac contractions. Thus, the functional effects are realized through both types of adrenergic receptors, while the metabolic effects are realized mainly through the β-adrenergic receptors.

Some pharmacologic receptors are sensitive to dopamine, serotonin, histamine, polypeptides, and other endogenous biologically active substances, as well as to the pharmacologic antagonists of some of these substances. The therapeutic action of a number of pharmacologic agents results from their specific effect on specific receptors.

REFERENCES

Turpaev, T. M. Mediatornaia funktsiia atsetilkholina i priroda kholinoretseptora. Moscow, 1962.
Manukhin, B. N. Fiziologiia adrenoretseptorov. Moscow, 1968.
Mikhel’son, M. Ia., and E. V. Zeimal’. Atsetilkholin. Leningrad, 1970.

B. N. MANUKHIN

receptor

[ri′sep·tər] (biochemistry) A site or structure in a cell which combines with a drug or other biological to produce a specific alteration of cell function. (physiology) A sense organ.

receptor

1. A channel-shaped, telescoping member which adapts the frame of a window to the size of the window opening; an adapter. 2. The shallow base pan for a shower.

receptor

[re-sep´tor] 1. a molecule on the cell surface (cell-surface or membrane receptor) or within a cell, usually in its nucleus (nuclear receptor) that recognizes and binds with specific molecules, producing some effect in the cell; e.g., the cell-surface receptors of immunocompetent cells that recognize antigens, complement components, or lymphokines; or those of neurons and target organs that recognize neurotransmitters or hormones.2. a sensory nerve ending that responds to various stimuli.

General sense receptors. (From Applegate, 2000.)α-r's (α-adrenergic r's) alpha-adrenergic receptors.adrenergic r's receptors for epinephrine or norepinephrine, such as those on effector organs innervated by postganglionic adrenergic fibers of the sympathetic nervous system. There are two types, alpha-adrenergic receptors and beta-adrenergic receptors.alpha r's (alpha-adrenergic r's) adrenergic receptors found in cardiac muscle and vascular smooth muscle; they are stimulated by norepinephrine" >norepinephrine and blocked by agents such as phenoxybenzamine" >phenoxybenzamine. They are subdivided into two types: α₁, found in smooth muscle, heart, and liver, with effects including vasoconstriction, intestinal relaxation, uterine contraction and pupillary dilation, and α₂, found in platelets, vascular smooth muscle, nerve termini, and pancreatic islets, with effects including platelet aggregation, vasoconstriction, and inhibition of norepinephrine release and of insulin secretion. Called also α-receptors and α-adrenergic receptors.β-r's (β-adrenergic r's) beta-adrenergic receptors.B cell antigen r's monomeric IgM, IgD, and (on memory cells only) IgG that is attached to the cell membrane of lymphocytes" >B lymphocytes (B cells); in conjunction with helper T cells, it triggers B cell activation on contact with antigen.beta r's (beta-adrenergic r's) adrenergic receptors that are stimulated by epinephrine" >epinephrine and blocked by agents such as propranolol" >propranolol. They are subdivided into two basic types: β₁-receptors are found in the myocardium and cause lipolysis and cardiac stimulation, and β₂-receptors are found in smooth and skeletal muscle and liver and cause bronchodilation and vasodilation. A third type, β₃, is atypical; it is more sensitive to norepinephrine than to epinephrine, relatively resistant to propranolol blockade, and may be involved in lipolysis regulation in adipose tissue. Called also β-receptors and β-adrenergic receptors.cell-surface receptor membrane receptor.cholinergic r's membrane receptors on cells of effector organs, innervated by cholinergic nerve fibers and responsive to the acetylcholine secreted by these fibers. There are two types, muscarinic receptors and nicotinic receptors.complement receptor a membrane receptor that can bind activated complement components. For example, component C3b binds to complement receptors of neutrophils, lymphocytes" >B lymphocytes, and macrophages.estrogen receptor a cellular regulatory protein that binds estrogenic hormones, found particularly in estrogen-sensitive tissues such as the uterus and breast. Cytoplasmic levels are measured in surgically removed breast carcinomas; high levels indicate that a positive response to endocrine therapy is likely.Fc r's specific membrane receptors for antigen-antibody complexes or aggregated immunoglobulins that bind a site in the Fc portion of the immunoglobulin molecule and may exhibit specificity for particular immunoglobulin classes. Fc receptors are found on B cells, K cells, macrophages, neutrophils, and eosinophils, and, during some developmental stages, on T cells.histamine r's receptors for histamine. H₁-receptors mediate contraction of smooth muscles and dilation of capillaries, causing effects such as bronchoconstriction and contraction of the intestine; they are blocked by antihistamines such as pyrilamine or chlorpheniramine. H₂-receptors mediate acceleration of the heart rate and produce gastric acid secretion; they are blocked by agents such as cimetidine.IgE r's membrane receptors for IgE, found on mast cells and basophils.insulin r's a type of membrane receptors specific for insulin, found on target cells.LDL r's (low-density lipoprotein r's) specific receptors for low-density lipoproteins found in coated pits on the surface of mammalian cells. The coated pits are internalized forming coated vesicles from which the receptors are recycled back to the plasma membrane while particles of low-density lipoprotein are transferred to lysosomes where they are degraded, releasing free cholesterol, phospholipids, and amino acids. Genetic defects in LDL receptors are responsible for familial hypercholesterolemia.membrane receptor a receptor located on or in the membrane of a cell. Called also cell-surface receptor.muscarinic r's cholinergic receptors on autonomic effector cells (and also on some autonomic ganglion cells and in some central neurons) that are stimulated by muscarine" >muscarine and parasympathomimetic drugs and blocked by atropine" >atropine.nicotinic r's cholinergic receptors of autonomic ganglion cells and motor end-plates of skeletal muscle that are stimulated by low doses of nicotine and blockaded by high doses of nicotine or by tubocurarine.olfactory receptor a specialized sensory nerve-ending sensitive to stimulation giving rise to the sensation of odors; called also osmoreceptor.

Structure of the olfactory receptors. (From Applegate, 2000.)opiate r's (opioid r's) receptors that combine with particular opiates to create analgesia and certain other effects. Several different ones have been identified and assigned Greek letters; the μ receptor gives superior analgesia, and the κ receptor is associated with a low degree of physical dependency.pain r's free nerve endings that are receptors for pain.stretch receptor a sense organ in a muscle or tendon that responds to elongation.T cell r's the characteristic marker of lymphocytes" >T lymphocytes (T cells) that recognize specific foreign antigens as well as self MHC antigens; both must be seen simultaneously to trigger T cell activation (see also lymphocyte activation). The receptor is not a complete immunoglobulin molecule but may contain heavy and light chain variable regions.

re·cep·tor

(rē-sep'tŏr, tōr), 1. A structural protein molecule on the cell surface or within the cytoplasm that binds to a specific factor, such as a drug, hormone, antigen, or neurotransmitter. 2. Any one of the various sensory nerve endings in the skin, deep tissues, viscera, and special sense organs. [L. receiver, fr. recipio, to receive]

receptor

(rĭ-sĕp′tər)n.1. Physiology A specialized cell or group of nerve endings that responds to sensory stimuli.2. Biochemistry A molecular structure or site on the surface or interior of a cell that binds with substances such as hormones, antigens, or neurotransmitters or is activated by events such as a change in the concentration of an ion.

re·cep·tor

(rĕ-sep'tŏr) 1. A structural protein molecule on the cell surface or within the cytoplasm that binds to a specific factor, such as a drug, hormone, antigen, or neurotransmitter. 2. Any one of the various sensory nerve endings in the skin, deep tissues, viscera, and special sense organs. [L. receiver, fr. recipio, to receive]

receptor

1. Any structure on or penetrating a plasma cell membrane or other membrane, capable of binding a specific external substance, such as a HORMONE, CYTOKINE, STEROID or NEUROTRANSMITTER, and, as a result, effecting a response within the cell. Plasma membrane receptors commonly respond by releasing a ‘second messenger’ within the cell. 2. A sensory nerve ending capable of receiving stimuli of various kinds and responding by the production of nerve impulses. The receptor has gradually come to be recognized as one of the fundamentally important entities in physiology, pathology, pharmacology and medical science generally.

receptor

any cell or organ of an animal capable of detecting a stimulus, i.e. a change in the external or internal environment, and which subsequently brings about a response in the behaviour of the animal. A receptor, for example the eye, receives and transforms stimuli into sensory nerve impulses. Receptors vary in complexity from the end of a sensory neurone to a sense cell and complex organs such as the eye. They may occur externally (EXTEROCEPTOR) or internally (ENTEROCEPTOR) or be positioned to receive body movement (PROPRIOCEPTOR). They also may be classified according to the type of stimulus received, e.g. PHOTORECEPTOR, THERMORECEPTOR, CHEMORECEPTOR,MECHANORECEPTOR, electro-receptor. See also REFLEX ARC. In microorganisms specific cell surface components act as receptors, for example for the adsorption of PHAGES (in phage infection) or for the attachment of SEX PILI (in bacterial CONJUGATION).

Receptor

A molecular structure in a cell or on the surface of a cell that allows binding of a specific substance that causes a specific physiologic response.Mentioned in: Alpha 1 -Adrenergic Blockers, Methadone

photoreceptor

A receptor capable of reacting when stimulated by light, such as the rods and cones of the retina. See cone cell; rod cell.

re·cep·tor

(rĕ-sep'tŏr) 1. A structural protein molecule on cell surface or within cytoplasm that binds to a specific factor. 2. Any sensory nerve endings in the skin or elsewhere.

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Synonyms for receptor

noun a cellular structure that is postulated to exist in order to mediate between a chemical agent that acts on nervous tissue and the physiological response

Related Words

noun an organ having nerve endings (in the skin or viscera or eye or ear or nose or mouth) that respond to stimulation

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