Health

How Sleep Works

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Sleep is a period of rest that alternates with wakefulness. You have internal body clocks that control when you are awake and when your body is ready for sleep. These clocks have cycles of approximately 24 hours. The clocks are regulated by multiple factors, including light, darkness, and sleep schedules. Once asleep, you cycle through the stages of sleep throughout the night in a predictable pattern.

Sleep is important because it affects many of your body’s systems. Not getting enough sleep or enough quality sleep raises your risk for heart and respiratory problems and affects your metabolism and ability to think clearly and focus on tasks. 

  

Your Sleep/Wake Cycle - How Sleep Works

Many factors play a role in preparing your body to fall asleep and wake up. Your body has several internal clocks, called circadian clocks. These typically follow a 24-hour repeating rhythm, called the circadian rhythm. This rhythm affects every cell, tissue, and organ in your body and how they work. Learn more in our Circadian Rhythms Disorders Health Topic.

Your central circadian clock, located in your brain, tells you when it is time for sleep. Other circadian clocks are located in organs throughout your body. Your body’s internal clocks are in sync with certain cues in the environment. Light, darkness, and other cues help determine when you feel awake and when you feel drowsy. Artificial light and caffeine can disrupt this process by giving your body false wakefulness cues.

Sleep Phases and Stages - How Sleep Works

When you sleep, you cycle through two phases of sleep: rapid eye movement (REM) and non-REM sleep. The cycle starts over every 80 to 100 minutes. Usually there are four to six cycles per night. You may wake up briefly between cycles. Sleep studies use sensors to record eye movements and brain activity, which are used to classify sleep phases and stages.