Longnecker's Anesthesiology > Part 8. Care of the Chronic Pain Patient > Chapter 90. Mechanisms of Chronic Pain Gary J. Brenner, MD, PhD, and Clifford J. Woolf, MD, PhD

Neurophysiology of Nociception

"The pain system has four basic anatomical components. Nociceptors are specialized high-threshold sensory afferent or primary sensory neurons that are located in the peripheral nervous system (PNS) whose peripheral terminals are capable of detecting or reacting normally only to intense noxious stimuli and transmit this information along their axons, which run in peripheral nerves to the spinal cord. Ascending nociceptivetracts, including the spinothalamic, spinobulbar, and spinohypothalamic tracts, convey nociceptive information from the dorsal horn of the spinal cord to higher centers in the central nervous system that are responsible for cognitive, affective, and complex motor responses to noxious stimuli as well as production of conscious awareness or perception of the stimulus and interaction with learned behaviors. Finally, descending systems in the CNS are involved in the processing or control of transfer of nociceptive information at multiple levels of the nervous system (Fig. 90–1).The high-threshold primary afferent neurons responsible for detection of high-intensity noxious stimuli are termed nociceptors. Nociceptors include both thinly myelinated A-delta (A-) and unmyelinated C-fibers. They represent one of several functional groups of sensory fibers in peripheral nerves (Table 90–1), including proprioceptors, low-threshold mechanoreceptors, and detectors of innocuous thermal stimuli. Nociceptors are classified based on..."