pain receptor

receptor /re·cep·tor/ (-ter)

1. a molecule on the surface or within a cell that recognizes and binds with specific molecules, producing a specific effect in the cell; e.g., the cell-surface receptors for antigens or cytoplasmic receptors for steroid hormones.

2. a sensory nerve ending that responds to various stimuli.

---

α-adrenergic receptors  adrenergic receptors that respond to norepinephrine and to such blocking agents as 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.

adrenergic receptors  receptors for epinephrine or norepinephrine, such as those on effector organs innervated by postganglionic adrenergic fibers of the sympathetic nervous system. Classified as α and β.

alpha-adrenergic receptors  α.

β-adrenergic receptors , beta-adrenergic receptors adrenergic receptors that respond particularly to epinephrine and to such blocking agents as propranolol. They are subdivided into two basic types: β1, in myocardium and causing lipolysis and cardiac stimulation, and β2, in smooth and skeletal muscle and liver and causing bronchodilation and vasodilation. The atypical type β3 may be involved in lipolysis regulation in adipose tissue.

cholinergic receptors  cell-surface receptor molecules that bind the neurotransmitter acetylcholine and mediate its action on postjunctional cells.

complement receptors  cell-surface receptors for products of complement reactions, playing roles including recognition of pathogens, phagocytosis, adhesion, and clearance of immune complexes. The best characterized are C1–C4, which bind C3 fragments already bound to a surface.

cutaneous receptor  any of the various types of sense organs found in the dermis or epidermis, usually a mechanoreceptor, thermoreceptor, or nociceptor.

cytokine receptors  membrane-spanning proteins that bind cytokines via extracellular domains, acting to convert an extracellular signal to an intracellular one.

H1 receptors , H2 receptors see histamine.

joint receptor  any of several mechanoreceptors that occur in joint capsules and respond to deep pressure and to other stimuli such as stress or change in position.

muscarinic receptors  cholinergic receptors that are stimulated by the alkaloid muscarine and blocked by atropine; they are found on automatic effector cells and on central neurons in the thalamus and cerebral cortex.

muscle receptor  a mechanoreceptor found in a muscle or tendon.

nicotinic receptors  cholinergic receptors that are stimulated initially and blocked at high doses by the alkaloid nicotine and blocked by tubocurarine; they are found on automatic ganglion cells, on striated muscle cells, and on spinal central neurons.

nonadapting receptor  a mechanoreceptor, such as a nociceptor, that responds to stimulation with a continual steady discharge and little or no accommodation over time.

olfactory receptor  a chemoreceptor in the nasal epithelium that is sensitive to stimulation, giving rise to the sensation of odors.

opiate receptor , opioid receptor any of a number of receptors for opiates and opioids, grouped into at least seven types on the basis of their substrates and physiological effects.

orphan receptor  a protein identified as a putative receptor on the basis of its structure but without identification of possible ligands or evidence of function.

pain receptor  nociceptor.

rapidly adapting receptor  a mechanoreceptor that responds quickly to stimulation but that rapidly accommodates and stops firing if the stimulus remains constant.

sensory receptor  receptor (2).

slowly adapting receptor  a mechanoreceptor that responds slowly to stimulation and continues firing as long as the stimulus continues.

stretch receptor  a sense organ in a muscle or tendon that responds to elongation.

tactile receptor  a mechanoreceptor for the sense of touch.

thermal receptor  thermoreceptor.

---

pain receptor,

any one of the many free nerve endings throughout the body that warn of potentially harmful changes in the environment, such as excessive pressure or temperature. The free nerve endings constituting most of the pain receptors are located chiefly in the epidermis and in the epithelial covering of certain mucous membranes. They also appear in the stratified squamous epithelium of the cornea, in the root sheaths and the papillae of the hairs, and around the bodies of sudoriferous glands. The terminal ends of pain receptors consist of unmyelinated nerve fibers that often anastomose into small knobs between the epithelial cells. Any kind of stimulus, if it is intense enough, can stimulate the pain receptors in the skin and the mucosa, but only radical changes in pressure and certain chemicals can stimulate the pain receptors in the viscera. Referred pain results only from stimulation of pain receptors located in deep structures, such as the viscera, the joints, and the skeletal muscles, and never from pain receptors in the skin.