The sympathetic nervous system in pain.

Pain and similar stressful behavioural states are characterized by organized neural responses of the somatomotor, somatosensory (analgesia), autonomic and neuroendocrine systems. These defensive behaviours consist of confrontational defence, flight and quiescence. These integrated reactions of the sympathetic nervous system are well-orchestrated responses of the different sympathetic pathways to cardiovascular and other target organs which prepare the body to meet threatening challenges. The neural basis of the autonomic reactions is to be found in the target-organ specific organization of the sympathetic pathways in the periphery and neuraxis. The spinal reflex pathways are relatively specific for putative nociceptive responses of the sympathetic nervous systems. The medulla oblongata and hypothalamus contain the circuits for the specific homeostatic regulations in which the sympathetic nervous system is involved. The mesencephalon (lateral and ventrolateral periaqueductal grey) and hypothalamus contain the neuronal programmes for the defensive mechanisms which are switched on when the organism is in pain and under stress.