The physiology of pain: a review

Pain is a complex physiological phenomenon that begins with the stimulation of free nerve endings in peripheral tissues and culminates in the perception of a physical and psychological state. The pain experience may be facilitated or inhibited through the action of several neurologic circuits which utilize several neurotransmitters. Therapeutic analgesia is achieved either through interference with pain-facilitating mechanisms or enhancement of pain-inhibiting mechanisms; practical applications are reviewed.