Principles & Practice of Pain Medicine, 2e > Part I. Pain: Biology, Anatomy, and Physiology > Chapter 3. Pathophysiology of Pain Stephen A. Cohen

Pathophysiology of Pain: Introduction

"Acute, nociceptive pain results from the complex convergence of many signals traveling up and down the neuraxis and serves to warn us of impending harm. The painful sensations ultimately leave the periphery and travel centrally, carried by the axons of the primary sensory neurons, the dorsal root ganglia (DRG), which are relatively quiescent unless specifically stimulated by sensory input. Unlike the "tombs" that the Belle of Amherst describes, however, if inflammation or injury damages the neural structures, pain sensation (neuropathic pain) may continue long after the noxious stimuli subside. The pain response can then harm rather than help the individual. Injured DRG may become hyperexcitable and display considerable spontaneous electrical activity. Such increased activity results from the expression of a dramatically different constellation of many cell-specific molecules in injured cells compared with normal ones. Ultimately, the operation of complex neuronal circuits may be markedly altered. Chronic pain sensation can result from such injury...."