Circadian Rhythm

agricultural-landscape-at-sunriseA circadian rhythm is a biological process that operates according to an approximately 24-hour clock. There is significant evidence that living creatures operate according to this internal clock and that biological processes are affected by a 24-hour day. The modulation of the sleep/wakefulness cycle is a classic example of a circadian rhythm. Some animals’ migration patterns are also influenced by circadian rhythms. Circadian rhythms are controlled primarily by light, not by temperature or other environmental cues.

How Circadian Rhythms Work
Circadian rhythms are strongly affected by darkness and light. Daily light changes send cues to the body about when to sleep, when to produce certain chemicals, and how to regulate energy levels. The “internal clock” is the suprachasmatic nucleus, which is a collection of cells located in the hypothalamus. This cluster of cells processes information about light and then uses this information to regulate daily cycles. Damage to this area results in the complete destruction of regular sleep/wakefulness cycles.

Circadian Rhythm Problems
While circadian rhythms function without conscious thought and regulate the processes of animals to a roughly 24-hour cycle, some factors can interfere with the functions of the internal clock. Circadian rhythm sleep disorder, for example, occurs when a person’s environment interferes with a normal sleep/wakefulness cycle. People who work night shifts and sleep during the day are susceptible to such disorders.

In areas where there are only brief periods of light or dark during certain times of the year, such as in the Arctic circle, animals must alter their circadian rhythms. When light lasts for extended periods of time, animals may slow down their internal clock. However, animals unaccustomed to these environments may suffer from body regulation problems if they travel to these areas.


  1. American Psychological Association. APA concise dictionary of psychology. Washington, DC: American Psychological Association, 2009. Print.
  2. Audesirk, T., Audesirk, G., & Byers, B. E. (2008). Biology: Life on earth with physiology. Upper Saddle River, NJ: Pearson Prentice Hall.

Last Updated: 06-15-2018

  • Leave a Comment
  • Amanda

    October 31st, 2016 at 12:27 AM

    Is it possible for head trauma to effect the circadian rhythm?

  • Diane

    December 29th, 2019 at 6:37 PM

    I can’t shut down my brain I’m always thinking about what I have to do days down the road unless I take a half of a loraspam what should I do

  • Susanne

    January 15th, 2022 at 10:36 AM

    Your favorite kind of pet will help you get some pure affection and daily walk. Control your to-do list by writing them down in order of priority of “have to’s”in red and “want to’s” in blue. Make check off boxes with starting and finishing dates. Play nature sounds before you go to bed such as ocean or rain forest. Get an encouraging daily note from a tear off calendar for your desk or place of work. Set up a campground in your backyard. Don’t try to finish a task in one one attempt. Rather break it into small bites. Do you eat the whole turkey at Thanksgiving? Mistakes make you a better person. Never, never, never, never, never, never, never, give up!

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