You've Got Some Nerve!
So the bossy brain sends all these messages around the body. How? By using nerves. Nerves are bundles of thin threads that carry messages throughout the body, a lot like how phone lines carry conversations. The name for this entire system of bundles is the nervous system, and it runs through the whole body just like those phone lines run through a city. Some of the messages go straight to the big boss, but a lot of them first go through a long bundle of nerves called the spinal cord. The spinal cord is inside your spine. Reach around and feel the bumps up and down the middle of your back - that's your spine.

Your eyes, ears, and skin are even working for your brain, sending messages through the nervous system about what's going on outside your body.Want an example of how all these parts work together?

Suppose you were at a friend's house, and his spiky cactus fell off the windowsill and was headed right for your leg. Your eyes would go to work right away, sending a message through your nerves to your brain: "WARNING, BOSS! SPIKY CACTUS HEADED TOWARD THE LEGS!" The brain would use the spinal cord and nerves to send a message to your leg muscles, telling them: "GET OUT OF THE WAY!" The brain even tells the muscles which way to move and how fast to move, all in a split second. This is an example of a voluntary movement. Your brain knew you should get away from the spiky cactus because it remembers that spiky things hurt. Ouch!

Snooze Time
The brain is always working. Even when you're sleeping, it's doing all kinds of things. Sleep is like a time-out for your body, so you can feel rested and prepared for the next day. But your brain never sits on the bench! Even as it's telling your body to sleep, parts of your brain are awake, taking control of how you sleep.

There are five stages of sleep, and your brain is in charge of each one. In the first stage, as you're drifting off to sleep, your brain tells your heart to beat slower and tells your body to lower its temperature a bit. It also sends messages to your muscles to relax.

In the second stage, you're in a light sleep. You might wake up from a noise or touch. But if your dog doesn't jump on the bed or start to bark, you progress to stage three. Now you're in a deep sleep. Your brain tells your blood pressure to go down, and you won't be very sensitive to the temperature of the air around you, either.

Then it's time for stage four, the deepest sleep yet. This is the stage where some people sleepwalk or sleeptalk. It's difficult to be awakened from this stage of sleep. The very last stage is called REM sleep. REM stands for rapid eye movement, because even though your muscles are totally relaxed, your eyes move back and forth quickly and your heartbeat increases. This is the stage when you dream. As the night goes on, you repeat stages two, three, four, and REM every 90 minutes - that's about four or five times a night! No wonder the brain is so busy!