Brain and Nerves
1. Nerves lead from the spinal cord or from the brain to each part of the body. Then they lead from each part of the body back to the brain or spinal cord. The brain and spinal cord are the centres of this system of nerves.
2. All parts of your body are connected by nerves. The nerve cells with their fibres make up the nervous system. When we study one nerve cell, we see that it has a long fibre at one end and short fibres at the other. The nerve cells send im-pulses to each other by means of the fibres at their ends. These fibres do not actually touch but are so close to each other that an impulse can travel from one fibre to another. Physical agents become stimuli for nerve terminals by transferring energy from the external object to the nerve terminals
3. Thus all nerve cells connect with each other. There are millions of these connecting nerve cells. Thus a stimulus from any part of the body can reach any other part of it. In the spinal cord and brain, the nerve cells connect with each other by their connecting fibres. Outside the spinal cord and brain, certain long fibres are grouped together to form nerves. Each nerve is made up of thousands of nerve fibres together in a bundle, as a cable is made up of separate wires.
The Brain Centre of the Nervous System
4. We know the nerves to carry impulses to the brain. We know that the brain sends these impulses along so that they go to the right place. The brain is made up of three parts. The cerebrum sits like a cap on the cerebellum. And the medulla is that long portion connecting the brain with the spinal cord. The cerebrum has certain parts that do certain work. Studying human beings with accidental injuries of brains helped scientists to get information about these areas. For instance they have discovered that the part for thought, memory, and feeling is found in the front of the cerebrum. The part for hearing is found at the side of the cerebrum, and the part for sight in the back of the cerebrum.
5. Many experiments have shown that the brain is the centre of feeling and understanding. The nerve cells in the brain can be «put to sleep» with ether or other anesthetics. Then the brain does not feel any impulses from the part being operated on. Sometimes the nerve cells near the part of our body being treated may be deadened by novocaine, as when the dentist pulls a tooth. What the novocaine does is preventing the impulses from getting to the brain from the nerve in the tooth.
6. The cerebellum is the centre for making your muscles work as a team. The medulla is the centre of certain of our most important acts: breathing and heartbeat, on which life itself depends. The medulla is also capable of controlling acts such as swallowing and yawning.