What you’ll learn to do: describe what happens to the brain and body during sleep

We devote a very large portion of time to sleep, and our brains have complex systems that control various aspects of sleep. Several hormones important for physical growth and maturation are secreted during sleep. While the reason we sleep remains something of a mystery, there is some evidence to suggest that sleep is very important to learning and memory.

You may not feel particularly busy while you sleep, but you’ll learn in this section that your brain and body are quite active. You pass through four different stages of sleep. In this section, you’ll learn more about these sleep stages, dreaming, and sleep disorders.