How Sleep Works

This content was created by the National Sleep Foundation


While you're off in dreamland, your brain and other body parts keep busy.

When you watch people sleep, they look peaceful. Their eyes are closed. Their breathing is slow. They make no sounds or movements. But you may be surprised to learn that underneath that calm exterior, the brain and other body parts are hard at work.

How You Fall Asleep

The simple act of falling asleep starts on the molecular level with something called a neurotransmitter—a chemical that acts on neurons (nerve cells) in the brain to tell your body whether it should be asleep or awake. The neurons, in turn, switch off the signals that help keep you awake.

Stages of Sleep

Once the neurons have told your body that it’s time to go to sleep, you'll pass through stages one through four of sleep, as well as REM (rapid eye moment) sleep.

Clearing Out Waste

Your brain is truly on overdrive during sleep, as it is working to clear itself of toxic byproducts that naturally accumulate throughout the day. Many neurological diseases are associated with a lack of sleep, perhaps because when you don't get your zzz's, your brain doesn’t have this chance to cleanse itself.

Cooling Down

One of the main functions of sleep is to conserve energy. That’s why your body temperature lowers by as much as 10 percent while you’re in dreamland.

Repairing Muscle

While you sleep, your body releases growth hormones that work to rebuild muscles and joints that may have been stressed during a workout or day-to-day activities. The more sleep you get, the better equipped your body will be to repair itself.

Breathing Slowly

When you’re awake, your breathing patterns vary greatly. You’ll breathe faster when excited and harder while exercising, for example. But during sleep, your breathing slows down and becomes very regular.

Reducing Heart Rate

One body part that gets a break during sleep is your heart. Your ticker works hard during the day, so at night during non-REM sleep it takes some pressure off itself by reducing heart rate, as well as blood pressure.