Anatomy and Physiology: The Central and Peripheral Nervous Systems
The Central and Peripheral Nervous Systems
The CNS, which includes the brain and spinal cord, has long been a source of mystery, for its functions are so complex, and the way those functions are carried out is not immediately obvious. The spinal cord is easier; using the knowledge we have learned about neurons, we can map regions and track reflexes, because its overall function is mainly to carry impulses from one place to another.
The brain, on the other hand, is far more complex and much subtler. I mean, compare it to the heart; both the function and the means of carrying it out is immediately visible, through the alternating contraction and relaxation of the atria and the ventricles. Now explain anger. How, let alone where, does the brain experience anger? We now know where (the amygdala), but we still don't know how!
A brain alone, however, is not enough. The nervous system must be able to communicate with all parts of the body. I always teach my students that three systems have physical connections with every part of the body: cardiovascular, lymphatic, and nervous. These nervous system connections allow sensory impulses to the brain (afferent), and motor impulses from the brain (efferent). Nerves of the PNS may be somatic in nature (sensing and moving the body in response), which is mainly voluntary, or those nerves may be autonomic in nature, which is involuntary.
Even if your train of thought leaves the station, at least part of your body is working in the background. This section discusses the architecture and workings of the two branches of the peripheral nervous system (PNS): the somatic nervous system (SNS) and the autonomic nervous system (ANS).
Excerpted from The Complete Idiot's Guide to Anatomy and Physiology © 2004 by Michael J. Vieira Lazaroff. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.