Pain: its physiology and rationale for management. Part I. Neuroanatomical substrate of pain.

Pain, one of man's most worrisome afflictions, is also one of neurobiology's most challenging problems. Even its definition is beset with controversy. The origin and current resolution of this controversy are presented in this paper, but the major purpose of Part I is to review the anatomical substrate of the peripheral and central nervous systems involved in pain. Structural and functional characteristics of pain receptors and their afferent fibers are described, with emphasis upon current hypotheses regarding putative neural transmitters and possible mechanisms for signal transduction. Hitherto unrecognized details of the cytoarchitecture, anatomical organization, and circuitry of the dorsal horns are reviewed. The paper concludes with a consideration of the major components of the ascending and descending systems of subserving pain.