Pain signalled by an intact somatosensory system serves an essential protective biological function. This is nociceptive pain. Rapid localization and identification of the nature of a painful stimulus is required to take appropriate action to avoid injury. This normal function is emphasized by the tissue destruction that may occur in conditions in which pain pathways are severely impaired, for example, in the peripheral neuropathies of leprosy and diabetes, or in the loss of spinothalamic tract function in the spinal cord in syringomyelia.