First Book in Physiology and Hygiene

by John Harvey Kellogg

8. The Spinal Cord.—There are a number of small holes in the skull through which the nerves pass out, but most of the nerves are bound up in one large bundle and pass out through an opening at the back part of the skull and runs downward through a long canal in the backbone. This bundle of nerves forms the spinal cord. The spinal cord contains cells also, like those of the brain. It is really a continuation of the brain down through the backbone.

BRAIN AND
SPINAL CORD.

9. Nerves from the Spinal Cord.—The spinal cord gives off branches of nerves which go to the arms, the chest, the legs, and other parts. One of the branches which goes to the hand runs along the back side of the arm, passing over the elbow. If we happen to strike the elbow against some sharp object, we sometimes hit this nerve. When we do so, the under side of the arm and the little finger feel very numb and strange. This is why you call this part of the elbow the "funny" or "crazy bone." The cells of the spinal cord also send out branches to the body and to other cells in the brain.

10. How we Feel.—If we cut or burn ourselves we suffer pain. Can you tell why it hurts us to prick the flesh with a pin, or to pinch or burn or bruise it? It is because the flesh contains a great many nerve-branches from the brain. When we hurt the skin or the flesh, in any way, these nerves are injured. There are so many of these little nerves in the flesh and skin that we cannot put the finest needle into the flesh without hurting some of them.

11. The Use of Pain.—It is not pleasant for us to have pain, but if the nerves gave us no pain when we are hurt we might get our limbs burned or frozen and know nothing about it until too late to save them.

12. Nerves of Feeling.—We have different kinds of nerves of feeling. Those we have learned about feel pain. Others feel objects. If you take a marble or a pencil in the hand you know what it is by the feeling of the object. This kind of feeling is called the sense of touch.

13. There are other nerves of feeling by means of which we are able to hear, see, taste, and smell, of which we shall learn in another lesson. Besides these we have nerves which tell us whether objects are cold or hot, and heavy or light. Nerves of feeling also tell us when we are hungry, or thirsty, or tired, and when we need more air to breathe.

14. Nerves of Work.—There are other nerves which are made just like the nerves of feeling, but which do not feel. These nerves have a very different use. They come from cells in the brain which have charge of the different kinds of work done in the body, and they send their branches to the parts which do the work; hence we call them nerves of work.

15. One set of cells sends nerves to the heart, and these make it go fast or slow as is necessary. Another sends nerves to the liver, stomach, and other digestive organs, and causes them to do their part in the digestion of the food. Other cells send branches to the muscles and make them act when we wish them to do so. Thus you see how very useful the brain and nerves are. They keep all the different parts of the body working together in harmony, just like a well-trained army, or a great number of workmen building a block of houses. Without the brain and nerves the body would be just like an army without a commander, or a lot of workmen without an overseer.