Figure 20.1: Staying balanced when riding a scooter requires control over the body’s muscles;
the nervous system controls the muscles and maintains balance. ( 9 )
What Does the Nervous System Do?
Thenervous systemis the body system that controls all the other systems of the body.
Controlling muscles and maintaining balance are just two of its roles. The nervous system
also lets you:
- Senses your surroundings with your eyes and other sense organs.
- Senses your internal environment, including temperature and pH.
- Controls your internal body systems and keeps them in balance.
- Prepares your body to fight or flee in emergency situations.
- Thinks, learns, remembers, and uses language.
The nervous system works by sending and receiving electrical messages. The messages are
carried by nerves throughout the body. For example, when Michael started to fall off his
scooter, his nervous system sensed that he was losing his balance. It responded by sending
messages to muscles throughout his body. Some muscles tightened while others relaxed. As
a result, Michael’s body became balanced again. How did his nervous system do all that
in just a split second? To answer this question, you need to know how the nervous system
carries messages.
Neurons and Nerve Impulses
The nervous system is made up of nerves. Anerveis a bundle of individual nerve cells. A
nerve cell that carries messages is called aneuron(Figure20.2). The messages carried by
neurons are referred to asnerve impulses.Nerve impulses are able to travel very quickly