pain
n. an unpleasant sensation resulting from damage to nerve tissue, stimulation of free nerve endings, or excessive stimulation (e.g., extremely loud sounds). Physical pain is elicited by stimulation of pain receptors, which occur in groups of myelinated or unmyelinated fibers throughout the body but particularly in surface tissues. Pain that is initiated in surface receptors generally is perceived as sharp, sudden, and localized; pain experienced in internal organs tends to be dull, longer lasting, and less localized. Although pain is generally considered a physical phenomenon, it involves various cognitive, affective, and behavioral factors: It is an unpleasant emotional as well as sensory experience. It may also be a feeling of severe distress and suffering resulting from acute anxiety, loss of a loved one, or other psychological factors (see psychic pain). Because of these various factors, as well as previous experience in pain response,
individual reactions vary widely. Psychologists have made important contributions to understanding pain by demonstrating the psychosocial and behavioral factors in the etiology, severity, exacerbation, maintenance, and treatment of both physical and psychic pain. See also chronic pain; gate-control theory.