ABSTRACT
The International Association for the Study of Pain has defined pain as an unpleasant sensory or emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Some definitions commonly used to characterize pain, its treatment, and its consequences are: Allodynia — Pain produced by non-noxious stimuli; Distress — Physical and emotional display of physical or mental strain or stress; Hyperesthesia — Increased sensitivity to non-noxious stimuli; Stress — Physical or mental discomfort; Suffering — Endurance of physical or mental strain or stress; and so on. Physiologic pain is produced by stimulation of nociceptors innervated by high-threshold A-delta and unmyelinated C fibers. The sensation of pain protects the body by warning of contact with tissue-damaging stimuli. Pathologic pain is caused by the ongoing activation of nociceptors due to peripheral tissue injury or injury to the nervous system. Peripheral pain is either visceral or somatic.
