What are Circadian Rhythms in Humans?

What is the definition of circadian rhythm?
Often referred to as the “body clock”, the circadian rhythm is a cycle that tells our bodies when to sleep, rise, eat–regulating many physiological processes. This internal body clock is affected by environmental cues, like sunlight and temperature.

circadian rhythm /sɜːrˈkdiən/ is any biological process that displays an endogenousentrainable oscillation of about 24 hours. These 24-hour rhythms are driven by a circadian clock, and they have been widely observed in plantsanimalsfungi, and cyanobacteria.[1]

The term circadian comes from the Latin circa, meaning “around” (or “approximately”), and diēm, meaning “day”. The formal study of biological temporal rhythms, such as daily, tidal, weekly, seasonal, and annual rhythms, is called chronobiology. Processes with 24-hour oscillations are more generally called diurnal rhythms; strictly speaking, they should not be called circadian rhythms unless their endogenous nature is confirmed.[2]

Although circadian rhythms are endogenous (“built-in”, self-sustained), they are adjusted (entrained) to the local environment by external cues called zeitgebers (from German, “time giver”), which include light, temperature and redox cycles. The medical condition of the circadian rhythm in humans is known as circadian rhythm disorder.



Circadian rhythms help determine our sleep patterns. The body’s master clock, or SCN, controls the production of melatonin, a hormone that makes you sleepy.

How do you reset your circadian rhythm?

Fortunately, there are some things people with delayed sleep phase syndrome can do to help reset their biological clocks:
  1. Schedule a doctor visit. …
  2. Adjust your bedtime. …
  3. Do not nap. …
  4. Do not sleep in. …
  5. Be strict about your sleep schedule. …
  6. Try light therapy. …
  7. Avoid night light.

How long is the human circadian rhythm?

Criteria. To be called circadian, a biological rhythm must meet these three general criteria: The rhythm has an endogenous free-running period that lasts approximately 24 hours. The rhythm persists in constant conditions, (i.e., constant darkness) with a period of about 24 hours.

What is the body’s natural sleep cycle?

Human circadian rhythms are regulated by an internal biological clock in the brain
Understanding your body’s internal clock—or circadian rhythm—is the first step to better sleep. Your circadian rhythm (also known as your sleep/wake cycle or body clock) is a natural, internal system that’s designed to regulate feelings of sleepiness and wakefulness over a 24-hour period.

How is body temperature affected during the circadian rhythm?

Researchers have found that fluctuations in internal body temperature regulate thebody’s circadian rhythm, the 24-hour cycle that controls metabolism, sleep and other bodily functions. The suprachiasmatic nucleus responds to light entering the eye, and so is sensitive to cycles of day and night.

What are some examples of circadian rhythms in humans?

There are many examples of circadian rhythms, such as the sleep-wake cycle, the body-temperature cycle, and the cycles in which a number of hormones are secreted. Infradian rhythms have a period of more than 24 hours.
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