The nervous system is made up of a brain and nerves. Messages travel between the nerves and brain. The messages are like small currents of electricity. Some of the nerves are connected to sense organs such as eyes. They send messages to the brain about what the sense organ has detected. The brain uses this information to decide what to do then sends messages along another set of nerves to the muscles. These messages make the muscles work. For example when a rabbit sees a fox approaching, its eyes send messages to the brain and the brain sends messages to its leg muscles to make the rabbit run.