Pain pathways and transmission.

Pain has been a major concern of humankind since the ancient times, and it remains one of the most important subjects of all health care professionals. Despite the obvious overwhelming clinical importance, the major advances in its diagnosis and therapy have been made only recently. "How do the sensory apparatus of the body and system of signal transmission relate to pain of peripheral origin?" is the topic of discussion. To do this, it is important to understand what constitutes the total pain experience. It consists of: 1) signal transduction at the peripheral receptor site, 2) signal conduction along the peripheral nerve, 3) pain modulation at the level of the spinal cord, 4) pain perception at the supraspinal site, and 5) the associated sensations, emotional reactions, and effective state. The signal transmission related to pain may be modified by various analgesic agents. Specific analgesic agent has a specific site of action which may be at peripheral receptors, at peripheral nerves, at the level of the spinal cord, at supraspinal levels by activating descending inhibitory systems, or at more cephalad levels by reducing the affective component of pain.