Friday, May 2, 2008

Nervous System Basics: Part I

In this series of posts I intend to bring out information found in one (just one) section of the 4-volume Encyclopedia of the Human Brain, 2002, edited by V.S. Ramachandran.

The section in question is written by Jay B. Angevine at the U. of Arizona, and begins page 313 in Vol. 3. He states the nervous system has:

*100 billion neurons of 10,000 types,
*1-10 trillion neuroglial cells,
*100 trillion chemical synapses,
*160,000 km. of neuronal processes,
*thousands of neuronal clusters and fiber tracts,
*hundreds of functional systems,
*dozens of functional subsystems,
*7 central regions, and
*three main divisions.

One hundred and sixty thousand kilometers, or about 100,000 miles of nerve fiber: the Bodyworlds Exhibit states that there are 72.5 kilometers (45 miles) of nerves, which are macro bundles of many fibers.. and that seemed a big number...

Angevine says, "... all of these parts form a coherent, bodily pervasive, diversified, complex epithelium with interdependent connectivity of neurons", most of which are interneurons rather than sensory or motor. The key organizing principles are centralization and integration (although there are many others as we will find out).

The nervous system performs the dual roles of regulation and initiation.
"In the first, it counteracts: responsively and homeostatically, gathering stimuli from outside and inside the body (including the brain), assessing their short-term and long-range significance, generating activity from faster breathing to stock trading, even to functional plasticity in learning or after brain damage.

In the other, it acts: endogenously, not so homeostatically, replacing one state of neural activity with another, generating activity from doing nothing at all to creative thinking and extraordinary achievement, even taking steps toward understanding how itself, the nervous system, works."

Angevine examines the overall organization of the nervous system from a number of perspectives in this section that runs 58 pages, and here I will delve into the third of ten sections he outlines, basic organizing principles, of which there are 8. I want to give each one of these principles some time and thought here.

No comments: