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(physiology), the capacity of a living organism to perceive stimuli from the external or internal environment.
An organism’s sensitivity to corresponding stimuli varies with the sensitivity of its sensory systems (analyzers). Sensibility is characterized by the threshold of stimulation: the lower the threshold, the higher the sensibility. A distinction is made between absolute and differential sensibility, that is, discriminative sensibility, and, accordingly, absolute and differential thresholds of stimulation. The absolute threshold is the minimum force of stimulation capable of producing a reaction. The differential threshold is the minimum amount of stimulation that has to be changed in order to change the response. Somatosensory sensibility (cutaneous sensibility and proprioceptive, that is, musclejoint, sensibility), visceral sensibility, and sensibility based on the activity of the sense organs are distinguished according to the sensory systems responsible for the perception of stimulation. Cutaneous sensibility is sometimes divided into coarse, protopathic, sensibility and fine, epicritic, sensibility. With respect to the type of stimulus, one can speak of sensitivity to mechanical, chemical, light, temperature, and other stimuli.
The sensibility of an organism may be judged from sensations and from objective criteria, for example, autonomic reactions and bioelectrical reactions. The thresholds, which are determined by various methods, may differ. For example, photosensitivity, determined from the bioelectrical activity of the brain, is higher than sensibility determined from the verbal responses of a subject regarding his sensations. Sensitivity to a stimulus is not a constant quantity and may change under the influence of a variety of factors, for example, during physiological adaptation, under the influence of efferent regulation, and as a result of the action of other stimuli. Pathological processes may cause a variety of disturbances of sensibility, depending on the place where a sensory system is affected: the peripheral portion (receptor), the conducting portion, or the central (including the cortical) portion.
REFERENCESGranit, R. Elektrofiziologicheskoe issledovanie retseptsii. Moscow, 1957. (Translated from English.)
Fiziologiia sensornykh sistem, part 2. Leningrad, 1972. (Rukovodstvo pofiziologii.)
O. B. IL’INSKII