In responding to stressors, whether physical or psychological, trivial or mortal, the autonomic nervous system plays a crucial role. This system influences cardiovascular, metabolic, and visceral activity in the resting organism and determines the physiologic concomitants of virtually every motion and emotion.

According to Langley’s conceptualization dating from approximately the turn of the twentieth century, the autonomic nervous system consists of the parasympathetic nervous system and the sympathetic nervous system. The former uses acetylcholine (ACh) as the main neurotransmitter, and the latter (with exceptions) uses the catecholamine norepinephrine (NE, noradrenaline). The adrenomedullary hormonal system uses the catecholamine epinephrine (EPI, adrenaline) as the main hormone secreted into the bloodstream.

Walter B. Cannon considered the adrenal gland to act in concert with the sympathetic nervous system to maintain homeostasis during emergencies, leading to the current use of the term sympathoadrenal system. As discussed in this chapter, however, recent evidence has indicated separate regulation of sympathoneural and adrenomedullary outflows during different forms of stress.1 In addition, a third peripheral catecholaminergic system may use dopamine (DA) as an autocrine-paracrine substance.