Autonomic Nervous System

Welcome back for the spring semester of A&P2! I figured that since it is all snowy (and icy!) outside, this polar theme would be the best to start us off.

General Function of the ANS:

The autonomic nervous system takes care of controlling those parts of our bodies that we don't think about or control purposefully. Basically, it controls our involuntary functions. For example, we might choose to spend 20 minutes on the stairmaster (or we might not!), but we do not choose to raise our heart rate and breathing rate while we are climbing those stairs. It happens automatically. That is due to the autonomic nervous system.

You will see that the ANS controls much more than just heart rate or breathing rate... it also controls glandular secretions, vasoconstriction (of blood vessels), the arrector pili muscles in our skin, digestive system movements, rate of kidney filtration, and more.

The ANS is thus said to be visceral, while the voluntary control from the CNS is considered somatic. Viscera are internal organs. And, remember, "soma" means body. Therefore, the ANS controls our organs through involuntary commands, while the CNS controls our body through voluntary commands.

How to understand the ANS:

The ANS is explained in numerous ways within any given textbook. One way to explain the ANS is to classify it into two subsystems based on function. You see, when the ANS controls rate of digestive movements, for example, it could either increase the rate or decrease the rate. It turns out that the ANS has somewhat segregated these two sides to each system effect (upregulation and downregulation) to the two subsystems. So, the subsystems typically oppose each other in action and can usually be called antagonistic. One subsystem is called the sympathetic nervous system and the other is the parasympathetic nervous system.

Another way it is explained is to describe its anatomy-- especially because you already know about neurons and the layout of the CNS, you now need to understand where the neurons are for the ANS (which is part of the peripheral nervous system, not the central nervous system). In order for the ANS to seem real to you, you have to learn where it is in the body, right? The two subsystems have slightly different anatomies, so their anatomies are typically described separately as well.

Yet another way to explain the ANS is to describe the types of neurons in the ANS and the neurotransmitters that each type uses.

If you tackle each of these ideas separately, you will probably have no problem with the ANS. It's just that these ideas are really interrelated, so they are hard to totally separate. And most textbooks get them muddled together somewhat. I probably will, too. So it will be up to you to try to think about each one on its own, so that you can master the ANS!

Some useful links:

	McGill University Nursing site about ANS (although many images don't work).
	Cambridge site for people that like words more than images.
	Very brief and clear description (below the first section on a different part of the PNS).