Pain and the sympathetic system.

Two reasons for thinking that the sympathetic nervous system plays a role in certain painful states are that the control of sympathetically innervated structures is abnormal and that the states are temporarily relieved by sympathetic blocks. The painful states in which the sympathetic system plays a role show extreme sensitivity on stimulation, both cutaneous and deep. The abnormal state spreads in a characteristic way. Comments on research on the sympathetic control of mechanoreceptors are given, and it is pointed out that the extreme sensitivity affects the mechanoreceptors; moreover, this sensitivity with the accompanying burning pain is removed by blocking the sympathetic supply of these receptors.