RECEPTOR

in biology, a specialized cell or group of cells that translates a certain type of stimulus, received from the environment or from within the organism, into nerve impulses that aid the organism in effecting future behavioral or physiological changes. Receptors are commonly provided with accessory structures that enable them to perform their function effectively; receptor and accessory structures constitute a sense organ. The eye of vertebrates is an organ of light reception (photoreception); the rod and cone cells of the retina are individual photoreceptors. A given receptor usually reacts only to stimuli of one general type (e.g., sound, light) and often only to a narrow range within the general type. An insect chemoreceptor may be stimulated by only one chemical compound. Sensory receptors are broadly classified by the types of stimuli to which they respond (photoreceptor, chemoreceptor, etc.). More broadly, they are sometimes categorized by the source of their stimuli, exteroceptors reacting to stimuli from outside the organism, enteroceptors to stimuli from within.