The Autonomic Nervous System

The Autonomic Nervous System

The second part of the nervous system to have a particularly powerful part to play in our emotional life is the autonomic nervous system. The autonomic nervous system is composed of two parts, which function primarily in opposition to each other. The first is the sympathetic nervous system, which starts in the spinal cord and travels to a variety of areas of the body. Its function appears to be preparing the body for the kinds of vigorous activities associated with “fight or flight,” that is, with running from danger or with preparing for violence.

Activation of the sympathetic nervous system has the following effects:

dilates the pupils
opens the eyelids
stimulates the sweat glands
dilates the blood vessels in large muscles
constricts the blood vessels in the rest of the body
increases the heart rate
opens up the bronchial tubes of the lungs
inhibits the secretions in the digestive system
One of its most important effects is causing the adrenal glands (which sit on top of the kidneys) to release epinephrine (aka adrenalin) into the blood stream. Epinephrine is a powerful hormone that causes various parts of the body to respond in much the same way as the sympathetic nervous system. Being in the blood stream, it takes a bit longer to stop its effects. This is why, when you get upset, it sometimes takes a while before you can calm yourself down again!
The sympathetic nervous system also takes in information, mostly concerning pain from internal organs. Because the nerves that carry information about organ pain often travel along the same paths that carry information about pain from more surface areas of the body, the information sometimes get confused. This is called referred pain, and the best known example is the pain some people feel in the left shoulder and arm when they are having a heart attack.

The other part of the autonomic nervous system is called the parasympathetic nervous system. It has its roots in the brainstem and in the spinal cord of the lower back. Its function is to bring the body back from the emergency status that the sympathetic nervous system puts it into.

Some of the details of parasympathetic arousal include...

pupil constriction
activation of the salivary glands
stimulating the secretions of the stomach
stimulating the activity of the intestines
stimulating secretions in the lungs
constricting the bronchial tubes
decreasing heart rate
The parasympathetic nervous system also has some sensory abilities: It receives information about blood pressure, levels of carbon dioxide in the blood, and so on.
There is actually one more part of the autonomic nervous system that we don't mention too often: The enteric nervous system. This is a complex of nerves that regulate the activity of the stomach. When you get sick to your stomach or feel butterflies when you get nervous, you can blame the enteric nervous system.