Circadian Rhythms

Overview | Study Guide | Online Quiz | Exercise Your Brain
Meet the Scientist | Links & Resources | Teacher Resources



OVERVIEW

What are circadian rhythms? The word circadian comes from the Latin roots circa, meaning around, and dies, meaning day. So, literally, circadian rhythm means a recurrent pattern of approximately one day. For this reason circadian rhythms are also called biological clocks. Most organisms exhibit circadian rhythms including cyanobacteria, plants, fruitflies, and mammals. For any organism, the study of how biological clocks work is called chronobiology.

What is the purpose of circadian rhythms? Organisms develop biological rhythms in response to the environmental patterns of the Earth. Examples of behaviors that are dependent on circadian rhythms are the sleep-wake cycle and core body temperature in humans, flowering and photosynthesis in plants, and locomotion and feeding in insects. By having an internal system to respond to environmental cues, such as the day-night cycle and the change of seasons, organisms can better organize their behavior and physiology. For instance, certain flowers will open at the time of day that coincides with the feeding time of their insect pollinators. This coordinated activity is beneficial to the flower as well as the insect.

Overall, circadian rhythms are molecular mechanisms that control various physiological activities based on a repeated and regularly timed rhythm or oscillation pattern.

Why This Science Matters

One of the most important results of our circadian rhythms is sleep and its regulation. Disrupting the sleep-wake cycle has considerable negative effects on alertness, concentration, and performance. Some medical ailments that result from interrupting the circadian sleep-wake cycle are jet-lag syndrome, sleep disorders, and Seasonal Affective Disorder (SAD). According to the U.S. National Center on Sleep Disorders, sleep problems cost the country $15.9 billion in annual medical bills.

Both adolescents and children need nine hours of sleep each night to do their best. Getting less than that, even by one hour, can diminish your alertness and ability to function. In addition, sleepiness can increase your risk of accidents and injuries and have negative effects on your school performance, extracurricular activities, and social relationships. These negative effects also happen to adults who do not get their recommended eight hours of sleep per night.


Human physiological changes over a 24-hour period.
Image credit: http://commons.wikimedia.org/wiki/File:Biological_clock_human.svg

 

     

©2005 Regents of the University of California. Terms and Conditions of Use.