Concepts of pain sensation and its modulation.

A review of the recent literature is presented on the basic physiological mechanisms by which pain (nociceptive) information is transferred in the peripheral and central nervous systems, as well as how this transmission is modified or modulated by endogenous mechanisms known to produce analgesia. The specific topics covered include the first sensory nerve fibers which conduct pain information into the spinal cord, the physiological properties and anatomical organization of the spinal cord mechanisms for transmission and modulation, the chemicals involved in synaptic transfer of information from the first to the second neurone in the sensory pathway and the major ascending nociceptive and descending antinociceptive pathways.