Why Zebras Don't Get Ulcers: The Acclaimed Guide to Stress, Stress-Related Diseases, and Coping (Third Edition)

It was acting erratically because, it turned out, the pituitary didn’t really have the whole hormonal game plan. It would normally be following orders from the brain,

If a neuron (or any cell) secretes a messenger that, instead, percolates into the bloodstream and affects events far and wide, that messenger is a hormone.

Thus, when the sympathetic nerve endings in your heart secrete norepinephrine, which causes heart muscle to work differently, norepinephrine is playing a neurotransmitter role.

There is another way as well—through the secretion of hormones.

The neural route represented by the sympathetic system is a first means by which the brain can mobilize waves of activity in response to a stressor.

It’s no surprise that it would be a disaster if both branches were very active at the same time, kind of like putting your foot on the gas and brake simultaneously. Lots of safety features exist to make sure that does not happen.

This parasympathetic component mediates calm, vegetative activities—everything but the four F’s.

Epinephrine is secreted as a result of the actions of the sympathetic nerve endings in your adrenal glands (located just above your kidneys); norepinephrine is secreted by all the other sympathetic nerve endings throughout the body. These are the chemical messengers that kick various organs into gear, within seconds.

(Adrenaline and noradrenaline are actually British designations; the American terms, which will be used from now on, are epinephrine and norepinephrine.)