Nervous System Basics

The nervous system is the body's communication network. It collects information from the environment, processes it, and sends instructions to the body about how to respond. Everything you think, feel, and do is controlled by the nervous system.

Main Parts of the Nervous System

• Brain — the control center of the body. Its largest part, the cerebrum, controls thoughts and memory; the cerebellum at the back controls balance and movement; the brain stem joins the brain to the spinal cord and controls breathing.
• Spinal cord — a thick bundle of nerves running down the back inside the spine. It carries messages between the brain and the rest of the body.
• Nerves — thin threads that carry electrical signals between the spinal cord and every part of the body.
• Sensory organs — the eyes, ears, nose, tongue, and skin. They collect information from the environment and send it to the brain.

How the Nervous System Works

1. Sensory organs detect a stimulus — for example, you see a ball coming toward you.
2. Signals travel along nerves to the spinal cord and up to the brain.
3. The brain processes the information and decides on a response.
4. The brain sends instructions back down the spinal cord and along motor nerves to your muscles.
5. You react — for example, your hand moves to catch the ball.

Neurons and Reflexes

• Neurons are specialized cells that carry electrical signals throughout the nervous system.
• A neuron has a cell body, dendrites (which receive signals), and an axon, or nerve fiber (which sends signals); sensory nerve endings detect heat, touch, and pain.
• Reflexes are automatic, rapid responses that protect the body — such as pulling your hand away from a hot surface — without waiting for the brain to decide.