Publisher's Synopsis
This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1904 edition. Excerpt: ... CHAPTER XI THE NERVOUS SYSTEM Parts of the nervous system.--The nervous system is composed of five important parts, (i) One large nerve-centre--the brain. (2) A long nerve-centre in the spinal column--the spinal cord. (3) Many small nerve-centres--the ganglia--found at many places in the body. (4) The nerves which run from the nerve-centres out to every part of the body. (5) Nerve endings, as where a nerve ends in a muscle or gland. The nerve-cell.--The nervous system is composed of cells just as other parts of the body are, but they are quite different in shape. A nerve-cell in the spinal cord may have to control a cell of muscle in the hand. It must then be able to reach all the way from the cord to the hand. So we find that most nerve-cells have long branches running out from them. 14 209 As a rule, there is only one very long branch and a number of small ones. In Fig. 68 you can see the parts of a nerve-cell. It has a body and a nucleus, and is composed of the same kind of material as the other cells; but it is different in having the long branch that may reach out two or three feet from the body of the cell to another cell over which it has control. When we use any of the skeletal muscles, we must first send an order out on the long branches of the nerve-cells to the muscle-cells. When a large number of these cells are clustered together they are called a nervecentre, and a number of the long branches bound together are called a nerve. All the nerve-centres are in the brain, the spinal cord, and the ganglia. Everything we do and every movement we make starts in the nerve-centres. The brain.--The brain is the most important part of the human body. It is very delicate and easily injured, and so we find it well protected. It is...
