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A daily cycle of activity observed in many living organisms. The "'circadian rhythm"' refers to the 24-hour cycle of biological processes that regulate numerous physiological activities in living creatures, including humans. These internal clocks, which are controlled by external elements such as light and temperature, regulate several aspects of an organism's behavior, physiology, and metabolism, including sleep-wake cycles, body temperature, hormone synthesis, and digestion.
== Circadian Rhythm ==


== Origin and Function ==
[[File:Circadian_rhythm_labeled.jpg|thumb|right|Diagram of the human circadian rhythm.]]


The term "circadian" is derived from the Latin words "circa" (around) and "diem" (day) and reflects the 24-hour cycle of these circadian rhythms. Circadian rhythms are endogenously created, or internally driven, but can also be altered by external stimuli, such as light, which assist synchronize the rhythm with the environment. This is referred to as "'entrainment"'.
The '''circadian rhythm''' is a natural, internal process that regulates the [[sleep-wake cycle]] and repeats roughly every 24 hours. It is driven by a circadian clock, and the term "circadian" comes from the Latin "circa diem," meaning "around a day." This rhythm is found in most living organisms, including animals, plants, and many tiny microbes.


The primary purpose of circadian rhythms is to optimize the physiological activities of an organism according to the time of day. For instance, in humans, the circadian rhythm helps prepare the body for nighttime sleep and daytime activity. It controls tiredness and alertness by regulating the release of hormones such as melatonin and cortisol.
== Biological Basis ==


== The Role of the Suprachiasmatic Nucleus ==
The circadian rhythm is controlled by the [[suprachiasmatic nucleus]] (SCN), a group of cells located in the [[hypothalamus]] of the [[brain]]. The SCN receives direct input from the [[retina]] of the eye, allowing it to synchronize with the external environment, particularly the light-dark cycle.


In animals, the suprachiasmatic nucleus (SCN) of the hypothalamus functions as the primary pacemaker of circadian rhythms. Around 20,000 neurons get direct input from the retina, enabling the SCN to detect changes in light and synchronize the circadian cycle accordingly.
=== Molecular Mechanisms ===


The SCN transmits messages to various regions of the brain and body, including the pineal gland, which regulates the production of melatonin, the hormone that controls sleep. When the SCN detects darkness, it sends a signal to the pineal gland to produce more melatonin, which induces sleepiness. In contrast, melatonin production reduces when light is detected, increasing wakefulness.
At the molecular level, circadian rhythms are generated by a set of core clock genes and proteins that form feedback loops. These include genes such as [[CLOCK]], [[BMAL1]], [[PER]], and [[CRY]]. These genes and their protein products interact in a complex network to produce oscillations in gene expression and protein activity that cycle over approximately 24 hours.


== Circadian Rhythm Disorders ==
== Functions of Circadian Rhythms ==


Many sleep and health issues can result from disruptions to the circadian cycle. The following are frequent circadian rhythm disorders:
Circadian rhythms influence various physiological processes, including:


* '''Delayed sleep phase disorder (DSPD)''': A disorder defined by difficulties falling asleep and waking up at customary times, resulting in a later-than-desired shift in sleep pattern.
* '''[[Sleep]]''': The sleep-wake cycle is one of the most well-known circadian rhythms. The SCN signals the [[pineal gland]] to produce [[melatonin]], a hormone that promotes sleep, in response to darkness.
* The opposite of DSPD, "'Advanced sleep phase disorder"' (ASPD) is characterized by a sleep pattern that is changed earlier than expected, with patients falling asleep and waking up earlier than normal hours.
* '''[[Hormone]] Secretion''': Hormones such as [[cortisol]] and [[growth hormone]] are released in a circadian pattern.
* '''Jet lag''' is a transitory circadian rhythm problem caused by rapid travel across many time zones, with symptoms including exhaustion, sleeplessness, and gastrointestinal difficulties.
* '''[[Body Temperature]]''': Body temperature fluctuates throughout the day, typically peaking in the late afternoon and reaching its lowest point in the early morning.
* '''Shift work sleep disorder''': A circadian rhythm disturbance encountered by those who work nocturnal hours or rotating shifts, resulting in difficulty with sleep, alertness, and general health.
* '''[[Metabolism]]''': Circadian rhythms regulate [[metabolic processes]], influencing appetite, digestion, and energy expenditure.


==Importance of Keeping a Healthy Circadian Rhythm==
== Disruption of Circadian Rhythms ==


Keeping a healthy circadian rhythm is essential for health and wellness as a whole. Many health conditions, including sleep disorders, obesity, diabetes, cardiovascular disease, and mood disorders, such as depression and anxiety, have been associated to circadian rhythm disturbances.
Disruptions to circadian rhythms can have significant health implications. Common causes of disruption include:


Practices that can help support a healthy circadian rhythm include:
* '''[[Jet Lag]]''': Rapid travel across time zones can desynchronize the internal clock from the local time.
* '''[[Shift Work]]''': Working at night or irregular hours can lead to chronic misalignment of circadian rhythms.
* '''[[Sleep Disorders]]''': Conditions such as [[insomnia]] and [[delayed sleep phase disorder]] are associated with circadian rhythm disturbances.


* Keeping a regular sleep routine
== Health Implications ==
* Experiencing natural light during the day
 
* Evening exposure to artificial light, especially blue light from screens, should be limited.
Chronic disruption of circadian rhythms has been linked to various health issues, including:
* Developing a soothing nighttime routine
 
* Caffeine and alcohol should be avoided close to bedtime.
* '''[[Cardiovascular Disease]]'''
* Developing an environment conducive to sleep that is cold, dark, and silent
* '''[[Obesity]]'''
{{Stub}}
* '''[[Diabetes]]'''
{{Light Ethology}}
* '''[[Mood Disorders]]''': Such as [[depression]] and [[bipolar disorder]].
{{DEFAULTSORT:Circadian Rhythm}}
 
[[Category:Circadian rhythm| ]]
== Circadian Rhythm in Other Organisms ==
 
Circadian rhythms are not unique to humans. In [[plants]], they regulate processes such as [[photosynthesis]] and [[flowering]]. In [[animals]], they influence behaviors such as [[migration]] and [[hibernation]].
 
== Related Pages ==
 
* [[Sleep]]
* [[Suprachiasmatic nucleus]]
* [[Melatonin]]
* [[Jet lag]]
* [[Shift work sleep disorder]]
 
[[Category:Chronobiology]]
[[Category:Sleep]]
[[Category:Sleep]]
[[Category:Biology of bipolar disorder]]
[[Category:Biological rhythms]]
[[Category:Plant cognition]]
<gallery>
File:Biological_clock_human.svg|Biological clock in humans
File:TOC1_interactions.jpg|TOC1 interactions
File:Jungpflanze_des_Seidenbaums_(Schlafbaum).png|Young plant of the silk tree (sleep tree)
File:Data_on_circadian_rhythm_of_gene_expression_in_four_seedlings._Two_of_these_Arabidopsis_thaliana_seedlings_carry_a_firefly_luciferase_reporter_for_transcription_of_the_gene_CCA1_and_two_for_TOC1.png|Data on circadian rhythm of gene expression in Arabidopsis thaliana seedlings
File:Drosophila_brains_and_the_circadian_system.jpg|Drosophila brains and the circadian system
File:Drosophila_circadian_rhythm.jpg|Drosophila circadian rhythm
File:Circadian_rhythm_labeled.jpg|Circadian rhythm labeled
File:Circadian_rhythm.svg|Circadian rhythm
File:Day_Sleepers_crop.jpg|Day sleepers
</gallery>

Latest revision as of 17:32, 18 February 2025

Circadian Rhythm[edit]

Diagram of the human circadian rhythm.

The circadian rhythm is a natural, internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours. It is driven by a circadian clock, and the term "circadian" comes from the Latin "circa diem," meaning "around a day." This rhythm is found in most living organisms, including animals, plants, and many tiny microbes.

Biological Basis[edit]

The circadian rhythm is controlled by the suprachiasmatic nucleus (SCN), a group of cells located in the hypothalamus of the brain. The SCN receives direct input from the retina of the eye, allowing it to synchronize with the external environment, particularly the light-dark cycle.

Molecular Mechanisms[edit]

At the molecular level, circadian rhythms are generated by a set of core clock genes and proteins that form feedback loops. These include genes such as CLOCK, BMAL1, PER, and CRY. These genes and their protein products interact in a complex network to produce oscillations in gene expression and protein activity that cycle over approximately 24 hours.

Functions of Circadian Rhythms[edit]

Circadian rhythms influence various physiological processes, including:

  • Sleep: The sleep-wake cycle is one of the most well-known circadian rhythms. The SCN signals the pineal gland to produce melatonin, a hormone that promotes sleep, in response to darkness.
  • Hormone Secretion: Hormones such as cortisol and growth hormone are released in a circadian pattern.
  • Body Temperature: Body temperature fluctuates throughout the day, typically peaking in the late afternoon and reaching its lowest point in the early morning.
  • Metabolism: Circadian rhythms regulate metabolic processes, influencing appetite, digestion, and energy expenditure.

Disruption of Circadian Rhythms[edit]

Disruptions to circadian rhythms can have significant health implications. Common causes of disruption include:

Health Implications[edit]

Chronic disruption of circadian rhythms has been linked to various health issues, including:

Circadian Rhythm in Other Organisms[edit]

Circadian rhythms are not unique to humans. In plants, they regulate processes such as photosynthesis and flowering. In animals, they influence behaviors such as migration and hibernation.

Related Pages[edit]

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