The ANS works on our body organs and involuntary functions.   Therefore, it could speed up or slow down the rate at which a certain organ functions.  Or it could cause blood flow to change.  Or it could cause increased or decreased glandular secretion.

    As you think about these functions, consider that some of them really go together.  For example, if your heart rate speeds up, often your breathing rate may speed up.  Or if you shiver, the hair on your skin is probably also going to stand up on end and blood flow will be decreased to your skin (you'll look pale).   Right?

    Well, the ANS is typically described as having two major classes of functions:

Note that these two functions directly oppose one another... you can't rest while you are fleeing.  Right?  Each function is carried out by a separate subsystem of the autonomic nervous system.  The "rest and digest" function is carried out by the parasympathetic nervous system (a.k.a., parasympathetic division of the ANS) and the "fight or flight" function is carried out by the sympathetic nervous system (a.k.a., sympathetic division of the ANS).

    Consider what happened to me on a visit to my sister's apartment when Elliot was 2.  As I was coming up the elevator to visit Elliot, and he and his nanny were hiding off to the side.  As soon as I stepped out of the elevator, they jumped out and said "hi."  You can imagine-- my heart seemed to race for a second and I was startled.  Their surprise wasn't really a scare, but my sympathetic nervous system started to kick in.  Elliot was so proud... he kept reminding me, saying "I hide... I hide."

    It takes turning off the sympathetic activation and also, sometimes, turning on the parasympathetic activation, to relax after a scare.

    You might also know from experience that you don't digest your food well when you are panicking.  Some students can't eat before a test because they get stomach aches.  This is because one action of the sympathetic nervous system on your digestive system is to slow it down (in addition to causing that panicked feeling).

    How can these two systems have such different, yet widespread, effects?  You will see two reasons that this is true:

1. Different subsets of neurons control each system
2. Different neurotransmitters are involved in each system

© 2006 STCC Foundation Press
written by Dawn A. Tamarkin, Ph.D.