[JOAN CARTAN-HANSEN] The brain weighs about 3 pounds. It's made up of 100 billion nerve cells or neurons. Electrical impulses pass from cell to cell. Messages go out of your brain, down your spinal cord and out to your body and then back again all in an instant. The brain, the spinal cord and all those nerves make up the nervous system. It's your body's information system.

[CHILD] Scientists say there's enough electricity from all those messages in your brain and body that turn on a light in a refrigerator.

[JOAN] The brain is made up of several parts. There's the brain stem. It controls your body's basic automatic functions like breathing. There's the cerebellum which controls things like movement, your physical skills. And then there's the limbic system. That makes up about 1/5th of your brain. There are glands like the pituitary and the hypothalamus. They work with the brain stem to control body temperature, growth and blood pressure. Then there's the cerebrum. That's the thinking, creative part of your brain. It's also the biggest part of your brain. Along with its thin covering - the cortex - it's the part of the brain that governs voluntary movements. It's where you think, where you perceive or sense things and because of your cortex you can understand and remember, communicate and create.

The brain has 2 sides. Each controls the opposite side of the body. Each side also controls certain skills. The right side of your brain controls music, art, the creative stuff and the left side handles numbers and words and problem solving. And there's a band of cells between the two parts or hemispheres of the brain so that the left side knows what the right side is doing.

[CHILD] The human brain is so soft that you could cut it with a butter knife. That's why you should wear your helmet when you ride your bike. You need to protect your brain.

[JOAN] Your brain and body also put out chemicals called hormones or neurotransmitters. Hormones help regulate your body's growth, help you mature, maintain your digestion - even tell you when to sleep. Neurotransmitters are chemicals that send messages between cells. Some neurotransmitters tell your heart to beat or your lungs to breathe while others help regulate your mood whether you're happy or sad. These chemicals play a part in how you remember things, why you dream, who you are.

Your thoughts and your feelings, your breathing and your growing are all controlled by your brain and your brain continues to develop even after you're born and continues to grow and change even as an adult. Your brain is what makes you, you.

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