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Teen Health

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Common Sleep Disorders in Teens

How Sleep Works

Everyone needs restful sleep to be energetic and alert, and to stay healthy. To help you understand how sleep affects you personally, let's look at how sleep works.

Sleep has five distinct stages, each with specific characteristics defined by your brain waves, eye movements, and muscle tension. There are two broad categories of sleep:

NREM sleep has four levels or stages. Stage 1 sleep, the lightest stage, is the transition from being awake to deeper sleep. Stage 2, intermediate sleep, accounts for 40% to 50% percent of your sleep time. Stages 3 and 4, called slow wave or delta sleep, are the deepest levels and occur mostly in the first third of the night. It is during delta sleep when your body heals itself. It is also difficult to awaken from delta sleep, as most of us feel dazed or groggy.

Sleep stages cycle every 90 to 120 minutes. During a normal night, there are about four to five sleep cycles.

Our circadian cycles -- that is, our internal "body clocks" -- determine our daily sleep cycles, performance, alertness, moods, and even our gastrointestinal functions and metabolism. Melatonin, a hormone made by the pineal gland in the base of the brain, is linked to the circadian system. Along with sunlight, melatonin helps to set the brain's biological clock. At night, melatonin is secreted, causing the body temperature to lower, and helping us sleep.

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