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A circadian rhythm,or circadian cycle,is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism and responds to the environment. Circadian rhythms are regulated by a circadian clock whose primary function is to rhythmically co-ordinate biological processes so they occur at the correct time to maximise the fitness of an individual. Circadian rhythms have been widely observed in animals,plants,fungi and cyanobacteria and there is evidence that they evolved independently in each of these kingdoms of life.
Chronobiology is a field of biology that examines timing processes,including periodic (cyclic) phenomena in living organisms,such as their adaptation to solar- and lunar-related rhythms. These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek χρόνος,and biology,which pertains to the study,or science,of life. The related terms chronomics and chronome have been used in some cases to describe either the molecular mechanisms involved in chronobiological phenomena or the more quantitative aspects of chronobiology,particularly where comparison of cycles between organisms is required.
The suprachiasmatic nucleus or nuclei (SCN) is a small region of the brain in the hypothalamus,situated directly above the optic chiasm. It is the principal circadian pacemaker in mammals,responsible for generating circadian rhythms. Reception of light inputs from photosensitive retinal ganglion cells allow it to coordinate the subordinate cellular clocks of the body and entrain to the environment. The neuronal and hormonal activities it generates regulate many different body functions in an approximately 24-hour cycle.
Non-24-hour sleep–wake disorder is one of several chronic circadian rhythm sleep disorders (CRSDs). It is defined as a "chronic steady pattern comprising [...] daily delays in sleep onset and wake times in an individual living in a society". Symptoms result when the non-entrained (free-running) endogenous circadian rhythm drifts out of alignment with the light–dark cycle in nature. Although this sleep disorder is more common in blind people,affecting up to 70% of the totally blind,it can also affect sighted people. Non-24 may also be comorbid with bipolar disorder,depression,and traumatic brain injury. The American Academy of Sleep Medicine (AASM) has provided CRSD guidelines since 2007 with the latest update released in 2015.
A zeitgeber is any external or environmental cue that entrains or synchronizes an organism's biological rhythms,usually naturally occurring and serving to entrain to the Earth's 24-hour light/dark and 12-month cycles.
Circadian rhythm sleep disorders (CRSD),also known as circadian rhythm sleep-wake disorders (CRSWD),are a family of sleep disorders which affect the timing of sleep. CRSDs arise from a persistent pattern of sleep/wake disturbances that can be caused either by dysfunction in one's biological clock system,or by misalignment between one's endogenous oscillator and externally imposed cues. As a result of this mismatch,those affected by circadian rhythm sleep disorders have a tendency to fall asleep at unconventional time points in the day. These occurrences often lead to recurring instances of disturbed rest,where individuals affected by the disorder are unable to go to sleep and awaken at "normal" times for work,school,and other social obligations. Delayed sleep phase disorder,advanced sleep phase disorder,non-24-hour sleep–wake disorder and irregular sleep–wake rhythm disorder represents the four main types of CRSD.
Melatonin receptors are G protein-coupled receptors (GPCR) which bind melatonin. Three types of melatonin receptors have been cloned. The MT1 (or Mel1A or MTNR1A) and MT2 (or Mel1B or MTNR1B) receptor subtypes are present in humans and other mammals,while an additional melatonin receptor subtype MT3 (or Mel1C or MTNR1C) has been identified in amphibia and birds. The receptors are crucial in the signal cascade of melatonin. In the field of chronobiology,melatonin has been found to be a key player in the synchrony of biological clocks. Melatonin secretion by the pineal gland has circadian rhythmicity regulated by the suprachiasmatic nucleus (SCN) found in the brain. The SCN functions as the timing regulator for melatonin;melatonin then follows a feedback loop to decrease SCN neuronal firing. The receptors MT1 and MT2 control this process. Melatonin receptors are found throughout the body in places such as the brain,the retina of the eye,the cardiovascular system,the liver and gallbladder,the colon,the skin,the kidneys,and many others. In 2019,X-ray crystal and cryo-EM structures of MT1 and MT2 were reported.
The PER3 gene encodes the period circadian protein homolog 3 protein in humans. PER3 is a paralog to the PER1 and PER2 genes. It is a circadian gene associated with delayed sleep phase syndrome in humans.
Period circadian protein homolog 1 is a protein in humans that is encoded by the PER1 gene.
A chronotype is the behavioral manifestation of underlying circadian rhythm's myriad of physical processes. A person's chronotype is the propensity for the individual to sleep at a particular time during a 24-hour period. Eveningness and morningness are the two extremes with most individuals having some flexibility in the timing of their sleep period. However,across development there are changes in the propensity of the sleep period with pre-pubescent children preferring an advanced sleep period,adolescents preferring a delayed sleep period and many elderly preferring an advanced sleep period.
Light effects on circadian rhythm are the effects that light has on circadian rhythm.
Serge Daan was a Dutch scientist,known for his significant contributions to the field of Chronobiology.
Charles Andrew Czeisler is a Hungarian-American physician and sleep and circadian researcher. He is a leading researcher and author in the fields of the effects of light on human physiology,circadian rhythms and sleep medicine.
A chronobiotic is an agent that can cause phase adjustment of the circadian rhythm. That is,it is a substance capable of therapeutically entraining or re-entraining long-term desynchronized or short-term dissociated circadian rhythms in mammals,or prophylactically preventing their disruption following an environmental insult such as is caused by rapid travel across several time zones. The most widely recognized chronobiotic is the hormone melatonin,secreted at night in both diurnal and nocturnal species.
A constant routine protocol is a common method used in human circadian rhythm research to study internally generated,or endogenous,circadian rhythms without the effect of external,or exogenous,influences. In the method,subjects are kept in constant conditions for at least 24 hours. These include constant light and temperature,as well as constant semi-recumbent posture. In addition,subjects' food intake is evenly distributed throughout the protocol,and subjects are typically not allowed to sleep for the duration. While in these conditions,subjects are often assessed for a number of variables of interest. Two of the most common and best understood of these variables are core body temperature and melatonin.
Familial sleep traits are heritable variations in sleep patterns,resulting in abnormal sleep-wake times and/or abnormal sleep length.
Dr. Debra J. Skene is a chronobiologist with specific interest in the mammalian circadian rhythm and the consequences of disturbing the circadian system. She is also interested in finding their potential treatments for people who suffer from circadian misalignment. Skene and her team of researchers tackle these questions using animal models,clinical trials,and most recently,liquid chromatography-mass spectrometry. Most notably,Skene is credited for her evidence of a novel photopigment in humans,later discovered to be melanopsin. She was also involved in discovering links between human PER3 genotype and an extremely shifted sleep schedules categorized as extreme diurnal preference. Skene received her Bachelor of Pharmacy,Master of Science,and Ph.D. in South Africa.
Charmane Eastman is an American academic research scientist whose career has focused on studying circadian rhythms and their relationships to sleep,jet lag,and shift work. She has also studied winter depression,more properly known as seasonal affective disorder (SAD). Of special focus are the effects of bright light and melatonin on circadian rhythms.
Anne-Marie Chang is a researcher in the fields of sleep and circadian rhythms and is currently an Assistant Professor of Bio-behavioral Health at Pennsylvania State University. She earned her Ph.D. in neuroscience from Northwestern University in 2003.
Elizabeth Klerman is a professor of neurology at Harvard Medical School. Her research focuses on applying circadian and sleep research principles to human physiology and pathophysiology. She also uses mathematical analysis and modeling to study human circadian,sleep,and objective neurobehavioral performance and subjective (self-reported) mood and alertness rhythms.
References
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- ↑ "BBC Radio 4 - The Life Scientific, Derk-Jan Dijk on the importance of sleep". BBC. Retrieved 7 October 2021.
- ↑ William H. Moorcroft (25 March 2013). Understanding Sleep and Dreaming. Springer Science & Business Media. pp. 63–. ISBN 978-1-4614-6467-9.
- 1 2 3 Dr. Amrit Lal (16 March 2014). Understanding the Language of Silence - Sleep, Sleep Behavior and Sleep Disorders. eBookIt.com. pp. 141–. ISBN 978-1-4566-2168-1.
- ↑ "First physical evidence of why you're an owl or a lark". New Scientist
- ↑ Dijk, DJ; Beersma, DG; Bloem, GM (1989). "Sex differences in the sleep EEG of young adults: visual scoring and spectral analysis". Sleep. 12 (6): 500–7. doi: 10.1093/sleep/12.6.500 . PMID 2595173.
- ↑ Dijk, Derk-Jan; Charles A. Czeisler (May 1995). "Contribution of the Circadian Pacemaker and the Sleep Homeostat to Sleep Propensity, Sleep Structure, Electroencephalographic Slow Waves, and Sleep Spindle Activity in Humans". The Journal of Neuroscience. 15 (5): 3526–3538. doi: 10.1523/JNEUROSCI.15-05-03526.1995 . PMC 6578184 . PMID 7751928.
- ↑ Dijk, Derk-Jan; Jeanne F Duffy; Eymard Riel; Theresa L Shanahan; Charles A Czeisler (19 April 1999). "Ageing and the circadian and homeostatic regulation of human sleep during forced desynchrony of rest, melatonin and temperature rhythms". The Journal of Physiology. 516 (Pt 2): 611–627. doi:10.1111/j.1469-7793.1999.0611v.x. PMC 2269279 . PMID 10087357.
- ↑ Dijk, Derk-Jan; Simon N. Archer; Antoine U. Viola; Vanessa Kyriakopoulou; Malcolm von Schantz (1 May 2008). "Inter-Individual Differences In Habitual Sleep Timing and Entrained Phase of Endogenous Circadian Rhythms of BMAL1, PER2 and PER3 mRNA in Human Leukocytes". Sleep. 31 (5): 608–17. doi:10.1093/sleep/31.5.608. PMC 2398752 . PMID 18517031.
- ↑ Viola, Antoine U.; Archer, Simon N.; James, Lynette M.; Groeger, John A.; Lo, June C.Y.; Skene, Debra J.; von Schantz, Malcolm; Dijk, Derk-Jan (2007). "PER3 Polymorphism Predicts Sleep Structure and Waking Performance". Current Biology. 17 (7): 613–618. doi: 10.1016/j.cub.2007.01.073 . PMID 17346965. S2CID 8133286.
- ↑ Dijk, Derk-Jan; Helen C. Thorne; Kay H. Jones; Stuart P. Peters; Simon N. Archer (2009). "Daily and Seasonal Variation in the Spectral Composition of Light Exposure in Humans" (PDF). Chronobiology International. 26 (5): 854–866. doi:10.1080/07420520903044315. PMID 19637047. S2CID 24293813.
- ↑ Archived 2013-11-13 at the Wayback Machine Society of Biology - List of fellows
- ↑ The Royal Society - Research Merit Awards