The Brain

Your brain is a true wonder of nature, probably the only one that wonders about itself. Humans take the brain for granted because it is part of their basic package, but brains are amazing things. Pound for pound, the human brain is the most complex piece of matter in the known universe. Sitting behind the protective shell of the skull, cushioned in a special liquid called cerebrospinal fluid, it is a living system composed of many billions of individual nerve cells called neurons, each of which is a highly complex system in itself, plus even larger numbers of glial cells which play a supporting role. Estimates of the total number of neurons in the human brain vary greatly, from 20 billion to a trillion, depending on which cells are included and how they are counted.

What structures make up the central nervous system?

The human nervous system consists of two main parts: (1) the central nervous system (CNS) consisting of the brain and spinal cord, and (2) the peripheral nervous system (PNS), consisting of nerves outside the brain and spinal cord, traveling to every part of the body.

The brain is pink and soft while living. Brain surgeons say it has the consistency of thick custard. Only when preserved for observation does the brain appear gray and claylike, as in specimen jars. Very conspicuous on the brain are large wrinkles or convolutions. These convolutions vastly increase the surface area of the brain.

The internet is full of good neuroimaging sites that show internal and external views of the brain. For example, the "three-dimensional brain fly-through" from GE Global Research is a small (2.5 meg) mpeg file that can be paused or reversed. It shows various regions of the brain on a 3-D simulated brain. Major regions such as lobes and the limbic system, discussed on the following pages of this chapter, are color coded and shown in isolation, to make their location easy to see. They aren't labeled, though, so you must learn the parts first in order to identify them.

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Copyright © 2007 Russ Dewey