Primary Afferents and Hyperalgesia

Abstract

Pain has two aspects. The first is its function as a warning system to ward off immediate threats. It is, in a sense, a necessary evil that serves to warn the organism of injury. But pain has another face, which we term hyperalgesia—the perceptual companion of inflammation, be it from infection, the mundane abrasion, a burn of the skin, or from the causalgia that mysteriously complicates only certain nerve injuries and cripples its victim. Save for the latter condition, where the pain seems to serve no apparent purpose, hyperalgesia seems not to be part of a warning system but instead is a reminder that something is wrong. A remarkable resetting of the threshold for pain occurs: the inflamed skin may become the source of increased pain merely by being lightly touched or gently warmed. The victim arduously protects the hyper-algesic part, which we infer may ultimately promote healing.