There is increasing awareness that the autonomic nervous system, through its central and peripheral pathways, plays a critical role in the regulation of the circulation. Peripherally, the autonomic representation, largely that of sympathetic nerves, innervate virtually all segments of the vascular tree as well as the adrenal medulla. Through the interaction of nerve terminals, their transmitters, receptors and intracellular mediators in smooth muscle, sympathetic neurons control vascular tone as well as the basal performance of the heart. In turn, the performance of the autonomic nervous system is highly controlled by the brain. Once viewed as a black box with only a vague influence on cardiovascular performance, the introduction of concepts and techniques of neuroscience into the field of cardiovascular medicine has led to the realization of the critical role of this organ in cardiovascular control.
It is now well recognized that within the brain, the represenation of cardiovascular function is highly restricted anatomically, engages a number of specific transmitters for its actions, and has highly selective and topographically restricted functions to influence circulatory performance.