To quickly review the main points covered in Chapter Seven, the most important part of the nerve system is the brain. The brain controls most of the body's activities. Messages between the brain and the spinal cord are carried by nerves, which are made up of special cells called nerve cells. Nerve cells are found in the brain, spinal cord, spinal nerves and the organs we use to see, hear, smell, taste and touch.

Nerve cells have long string-like fibres that carry messages. These fibres have branched ends to send and receive messages. Remember that nerve cells are so small they cannot be seen without a microscope. But one fibre from a nerve cell may stretch as long as three feet.

There are many kinds of nerve cells, and this chapter deals mainly with three kinds. The sensory nerve cells carry messages of heat, light, sound and pressure from the skin, muscles and organs inside the body. Motor nerve cells carry messages to the muscles, and this causes the muscles to move. Connecting nerve cells go between the sensory nerve cells and the motor nerve cells.

After the messages go from the spinal cord to the brain, the brain sends messages through the motor nerve cells to the muscles. All these different nerve cells help us to see, hear, taste, smell and feel. Now if you have no further questions about Chapter Seven, we'll go on to talk about the chemical processes involved in this transfer of messages.