The nervous system reaches every part of the body and controls everything that is done, even thinking itself. The chief divisions of the nervous system are the brain and spinal cord. From these divisions nerves extend into all the tissues and carry messages to and fro.
The headquarters, or brain.
The real headquarters of the nervous system is the part called the brain. This is a mass of tender tissues weighing from two and· one-half to three pounds. The upper and larger part of the mass of tissues is called the cerebrum. The outer part of the cerebrum, known as the cortex, consists of gray matter arranged in many folds. Just below the cerebrum is a much smaller part of the brain, the cerebellum. Below the cerebellum is a third part which connects the brain to the spinal cord. The brain receives messages from various parts of the body and from outside the body. It gets the messages from the outside through five leading sense organs: the eyes, ears, nose, mouth, and skin. Also it directs many of the activities of the body, as talking, reading, and playing. Often the messages received determine what it directs the body to do.
The brain is the center for thinking. When you solve a problem in arithmetic, your brain does the work. When you choose a game to play on the playground, your brain makes the decision. Often you use your brain, as in studying, without using any other part of your body. At other times you think as you act, watching everything that you do, as in writing. You carry on many activities, such as walking, however, with little or no thought. You may walk down the street or road, for instance, and never think about the particular movements of your feet and legs. This is because you have used them in walking so much that they are able to take care of themselves. Any activity which may be carried on in this way is a habit. Habits mean much to a person, for they enable him to do many things he could not do if he had to think of every activity.
The spinal cord.
The spinal cord extends from one end of the backbone to the other and looks like a heavy piece of wrapping cord. This is because it is made up of many smaller cords and fibers. Really it is a bundle of nerves. The spinal cord extends through the center of the spinal column, which protects it from injury. Branches of separate nerves extend from the spinal cord on either side to other parts of the body. Certain parts of the spinal cord act somewhat like the brain. They receive messages and direct activity. Thus, if you burn your finger on a hot stove, you jerk your hand away before you have time to think. Other activity under the control of the spinal cord keeps going night and day. This includes the action of all the vital organs, such as the heart, stomach, and liver. A special set of nerves connected with the spinal cord looks after this work. All such work, of course, is not under a person’s control, but he may do something that affects it. Being angry at the table, for example, may interfere with digestion.
Two kinds of nerves.
There are two chief kinds of nerves in the nervous system of the body. One kind, known as the sensory nerves, send messages to the brain of what is taking place, and keep the body informed. They are especially numerous in the tips of the fingers and the tip of the tongue but are found in large numbers nearly everywhere in the body. Most of them, of course, are found in the skin, eyes, ears, nose, and mouth. They are called sensory because they make possible the five special senses of feeling, sight, sound, smell, and taste.
The other kind of nerves, known as motor nerves, controls the movements of the body. They are attached to the muscles and make them do what the brain orders. For example, a person may put his hand in his pocket to get a knife. The sensory nerves tell him how to tell the knife from various other things, such as money or keys, that may also be in his pocket. When his fingertips feel the knife, the motor nerves tell the hand to take hold of it and bring it out.
What the nerves are like.
Nerve tissue is made up of living cells which have tiny branches extending out at each end. Some of the branches receive messages, while others deliver orders, depending upon whether they are parts of sensory or motor nerves. All of the cells are connected in a great network throughout the body. A number of cells together make up a single nerve. When a message is picked up in one sensory cell, it is passed along to the next, and so on, until it reaches the spinal cord or the brain. In the same way, a message is returned from cell to cell over motor nerves. Thus a message of pressure on a person’s toe may be sent from cell to cell until it reaches the spinal cord. The cord may send an order back to the muscles to move the foot as quickly as possible. A second later the brain gets a report of both the pressure and the movement, and the person says, “Someone stepped on my toe.”
Taking care of the nerves.
The nerves, like other parts of the body, require care if they are to work well. When they fail a person, his whole body begins to break down. Everything that helps other parts of the body, such as good food, fresh air, exercise, and rest, usually helps the nerves. Rest, perhaps, helps more than anything else. The nerves, like the muscles, may often be rested by changing from one activity to another. Thus if a person begins to feel nervous or restless from driving an automobile, he should stop and walk around for a while or do anything else that will lessen the strain. To keep on driving when he is tired may cause him to have an accident. Also, of course, a person should get plenty of sleep, as this is the best means of refreshing the nerves.
The nerves are always greatly affected by worry or anger. Strangely, it seldom, if ever, does a person any good to worry, and it may cause a great deal of harm. In fact, it tends to upset his whole nervous system, making him uneasy for a long period of time. Anger, on the other hand, acts more quickly. When a person is angry he may suddenly lose control of himself and do something which he would never do under any other conditions. In order to have healthy nerves, too, a person should strive to be happy. Above everything else, he should fight worry and anger, as they are two of his greatest enemies.