Your body's control center.

Imagine trying to throw a ball if only the cells in your fingers decided to cooperate--it sure wouldn't go very far! Instead, the cells that make up the tendons in your fingers and the muscles in your arm all work together. At the same time, your eyes are working to see where to throw the ball, your legs are working to balance your shifting weight, and your heart and lungs are working to circulate blood and oxygen throughout your body. That's a lot of work!

Each of the billions of cells in your body has a specific function. But cells also have to work together to get important jobs done. Your cells are able to work together because a special group of cells organizes and directs the action. These cells make up the brain and spinal cord. Together they're called the central nervous system.

Nerve cells outside of the brain and spinal column are called the peripheral (puh-RIF-ur-ul) nervous system. The peripheral nerves are constantly sending messages in the form of tiny electrical pulses to your brain. These messages come from places like your skin, eyes, tongue, muscles, and ears. The brain's job is to sort out all these messages and direct various parts of your body to take action. The brain does this by sending out its own messages that tell groups of cells what to do.

Your brain is responsible for keeping your internal organs, including your heart and lungs, working properly--and continually. Your brain makes these decisions automatically, without you having to think about it. Automatic functions, like breathing, food digestion, and even blinking, are believed to be controlled by a part of the brain called the hypothalamus (yi-po-THAL-uh-mus). Other areas of the brain are responsible for thinking, talking, emotions, memory, imagination, and more.

While the brain takes care of these many functions, the spinal cord handles some of the "emergency" messages. For instance, if you touch a hot surface, nerve signals race to the spinal cord and cause an automatic response--you quickly pull your hand away! This is called a reflex action. The nerve signal continues up to the brain, where the information about what has happened is analyzed. Your brain might then tell you, "Well, we won't do that again!"

The thinking part of your brain, plus those areas that control your body's automatic and reflex actions, allow all your cells to work together. The complex web of nerve cells that make up your peripheral nervous system provides the pathways for nerve signals to travel to and from all parts of your body. These vital systems allow you to breathe, blink, and throw a ball--all at the same time!