What Is the Circadian Rhythm?

By jolene
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The circadian rhythm is the internal process that functions to regulate the sleep-wake cycle. It is a natural process that repeats about every 24 hours. The circadian rhythm can refer to biological processes that displays endogenous oscillation of about 24 hours. These rhythms that occur every 24 hours are driven by a circadian clock and can be observed in various fungi, plants, animals, and cyanobacteria.

The term “circadia” originates from the Latin term “circa,” which translates to approximately or around. The formal study of these rhythms that occur daily, weekly, seasonal, or annual is known as chronobiology. Although these rhythms are endogenous, they are also dependent on the environmental cues such as temperature and light. When there is an abnormal circadian rhythm, it is called a circadian rhythm disorder. In 2017, Michael Young, Michael Rosbash, and Jeffrey Hall were awarded the Nobel Prize in Physiology or Medicine due to their discovery of molecular mechanisms that control the circadian rhythm in fruit flies.

1. History

Androsthenes from the 4th century BC described diurnal leaf movements from a tamarind tree. In Chinese medical texts, the circadian or diurnal process was mentioned dating back to the 13th century. In 1729, a French scientist noted endogenous circadian oscillation in the 24-hour patterns of the leaf movements of Mimosa pudica despite being kept in total darkness.

By 1896, there was an observation where sleepiness increases and decreases in a 24-hour duration after prolonged sleep deprivation. In 1918, animals were found to be capable of maintaining a 24-hour pattern despite the absence of light and temperature cues. After several more discoveries throughout the years, in 1977, the term “circadian” was adopted. In 1994, the first mammalian circadian clock mutation was discovered in mice by Joseph Takahashi.

Circadian Rhythm

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