Physiology of Nociceptors

Nociceptors are a specialized class of primary afferents that respond to noxious or injurious stimuli. Unmyelinated (C-fiber) nociceptors are responsible for the burning pain sensation from noxious heat stimuli and from prolonged mechanical stimuli. Myelinated (A-fiber) nociceptors are thought to be responsible for the sharp, pricking pain associated with application of intense heat or sharp objects. An enhanced pain in response to cutaneous stimuli (primary hyperalgesia) develops at the site of tissue injury and is thought to be mediated by an enhanced responsiveness (sensitization) of primary afferent nociceptors. Hyperalgesia also develops in a large area of uninjured skin surrounding the injury site (secondary hyperalgesia) and most likely is due to sensitization of neurons in the central nervous system.