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What makes us sleep?

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Patterns of sleep are regulated by two processes working together: sleep drive and the circadian (pronounced sur-KAY-dee-uhn) clock.

  • Sleep drive. The need for sleep is driven by the length of time you are awake. The longer you are awake, the greater your drive or "need" to sleep.1 The drive to sleep continues to build within your body until you are able to sleep.
  • Circadian clock. Your body has a natural clock, called a "circadian clock," which helps you regulate your sleep. The word "circadian" refers to rhythmic biological cycles that repeat at approximately 24-hour intervals. These cycles are also referred to as circadian rhythms. Your circadian clock is strongly influenced by light, which is the reason that people living in different regions have different sleeping schedules. This is also the reason that your sleeping patterns tend to vary due to the amount of light and darkness present.2

At bedtime, when your drive to sleep is greatest, your sleep drive and circadian clock work together to allow you to fall asleep. After you have slept for a while, when your drive to sleep is lower, your circadian clock allows you to stay asleep until the end of the night.


  1. Romeijn, N., Raymann, R. J., Møst, E., Te Lindert, B., Van Der Meijden, W. P., & Fronczek, R. (2012). Sleep, vigilance, and thermosensitivity. European Journal of Physiology, 463, 169-176. [top]
  2. National Institute of Neurological Disorders and Stroke. (2007). Sleep and circadian rhythms. InBrain basics: Understanding sleep. Retrieved May 29, 2012, from http://www.ninds.nih.gov/disorders/brain_basics/understanding_sleep.htm#circadian_rhythms [top]

Last Updated Date: 07/31/2013
Last Reviewed Date: 07/09/2013
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