9781422280386

Chapter One

The Brain and Nervous System W alking. Talking. Sleeping. Seeing. Thinking. All of these activities are controlled by the most amazing structure in the human body: the nervous system. Run by your brain, your nervous system makes you the unique person you are. It connects you to the world through your senses. Your brain collects all the information you gather by seeing, hearing, touching, smelling, tasting, and moving. But it doesn’t just store that information, like a computer’s hard drive might. Your brain learns from everything you do and experience. Your brain can make decisions in a split second. If you touch something too hot on the stove, your brain immediately sends a message along the spinal cord, telling your muscles to pull your hand back, and it makes a memory of the experience so that you’ll know to be careful around the stove next time. Your brain can also make decisions based on evidence accumulated over a long period of time. If your dad makes a joke at dinner, your brain tells you to laugh—or groan—depending on how many times he’s already told that joke and how funny it was the first time.

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