The Autonomic Nervous System Has Parts

The autonomic nervous system has parts, it’s not one thing.  It’s not like you got your autonomic system pumping or something like that.  In fact, it’s very important to understand that there are components of the autonomic nervous system.

The English physiologist, John Newport Langley, who coined the term “autonomic nervous system,” had three components in mind: the enteric nervous system, meaning/referring to the wall of the gut, the parasympathetic nervous system, which is another phrase that Langley coined, and the sympathetic nervous system.  Sympathetic nervous system is actually an ancient phrase. It was introduced but from the teachings of Galen, the Second Century Greek physician whose ideas dominated medical thought and practice for about 14 centuries until the discovery of the circulation of the blood by William Harvey.  Galen taught that the body has spirits – animal spirits, vital spirits, natural spirits. And the animal spirits would be distributed in the body by tubes, now they’re called nerves, and because of this distribution the organs of the body would work in harmony with each other, in concert with each other, in sympathy with each other.  So, that’s the origin of the phrase sympathetic nervous system.  Nobody’s come up with very good evidence for the existence of the spirits, we are working on that, but the idea that the sympathetic nervous system somehow plays a role in coordination of the actions of different organs of the body is essentially correct.

In the early 20th Century, the great American physiologist, Walter B. Cannon, introduced another part of the autonomic nervous system which was hormonal – the sympathetic-adrenal-medullary-system, or sympathetic adrenergic system.  Cannon thought that the sympathetic nervous system and the adrenal medulla, the source of adrenaline or epinephrine, worked together as a unified kind of a monolithic system to respond to emergencies and to maintain homeostasis, a word that Cannon invented.  Cannon became so convinced that the sympathetic and adrenal medullary system, the sympathoadrenal system, or sympathetic-adrenal-medullary-system, worked as a unit, that in the 1930s, he formally proposed that adrenaline, the hormone coming from the adrenal medulla, is also the neurotransmitter of the sympathetic nervous system. And he was wrong, and this probably cost him a Nobel prize because the person who did identify norepinephrine as the sympathetic neurotransmitter, von Euler, in mid 1940s, shared a Nobel prize for that discovery.

So, there are four components, but a fifth component is introduced by Sir Henry Dale and that has to do with sweating, the sympathetic cholinergic system.  So, there are at least five components of the autonomic nervous system.  Remember the autonomic nervous system is not autonomous and as you can see it’s not a single system either, it has components, it’s not even a nervous system necessarily because of this hormonal component, the sympathetic adrenergic system.