The autonomic system is divided into two divisions … the sympathetic and parasympathetic. The parasympathetic is activate the majority of the time. It is active during periods of rest and mediates digestion, evacuation of the bowel and bladder, sleep and procreation. It uses a few long nerves that run from the spinal cord to reach a ganglion (cluster of neurons) located close to their target organ. From here short nerves carry the signal on to the organ.
The sympathetic system is active during periods of stress. The sympathetic nerves also depart from the spinal cord but they terminate on ganglions located next to the spinal column. From there many long nerves carry the signal on to several destinations, however most of the effect of the sympathetic system occurs through the use of epinephrine released by the adrenal glands. Epinephrine (adrenaline) is a hormone that is released into the blood circulation when a sympathetic nerve running from the spinal cord to the adrenal glands is activated by the hypothalamus. Adrenaline binds to receptors found on various organs throughout the body resulting in a constellation of immediate changes preparing the body for ‘fight or flight’. The heart beats faster, the blood is shunted to the muscles, the pupils dilate so as to optimize vision, attention increases, and muscle reflexes are potentiated. Simultaneously, unnecessary processes such as digestion, elimination of the bladder, and procreation are quashed.
There are many practitioners, myself included, who believe that many chronic diseases and ailments are a consequence of inappropriately high adrenal tone from a perpetually activated sympathetic system. A healthier life can be achieved by taking steps to lowering the level of the circulating stress hormones and fostering a state conducive to higher parasympathetic tone.