Circadian rhythm - Knowledge

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circadian mechanism they developed profound cardiovascular and renal disease; however, when the Tau animals were raised for their entire lifespan on a 22-hour daily light-dark cycle they had a healthy cardiovascular system. The adverse effects of circadian misalignment on human physiology has been studied in the laboratory using a misalignment protocol, and by studying shift workers. Circadian misalignment is associated with many risk factors of cardiovascular disease. High levels of the atherosclerosis biomarker, resistin, have been reported in shift workers indicating the link between circadian misalignment and plaque build up in arteries. Additionally, elevated triacylglyceride levels (molecules used to store excess fatty acids) were observed and contribute to the hardening of arteries, which is associated with cardiovascular diseases including heart attack, stroke and heart disease. Shift work and the resulting circadian misalignment is also associated with hypertension.

1228:. It is based on its predecessor, the PER model where it was explained how the PER gene and its protein influence the biological clock. The model includes the formation of a nuclear PER-TIM complex which influences the transcription of the PER and the TIM genes (by providing negative feedback) and the multiple phosphorylation of these two proteins. The circadian oscillations of these two proteins seem to synchronise with the light-dark cycle even if they are not necessarily dependent on it. Both PER and TIM proteins are phosphorylated and after they form the PER-TIM nuclear complex they return inside the nucleus to stop the expression of the PER and TIM mRNA. This inhibition lasts as long as the protein, or the mRNA is not degraded. When this happens, the complex releases the inhibition. Here can also be mentioned that the degradation of the TIM protein is sped up by light. 940: 1134: 764:, the physiological reaction of organisms to the length of day or night, is vital to both plants and animals, and the circadian system plays a role in the measurement and interpretation of day length. Timely prediction of seasonal periods of weather conditions, food availability, or predator activity is crucial for survival of many species. Although not the only parameter, the changing length of the photoperiod (day length) is the most predictive environmental cue for the seasonal timing of physiology and behavior, most notably for timing of migration, hibernation, and reproduction. 1618:, may also benefit patients with hypertension (high blood pressure) by significantly increasing efficacy and reduce drug toxicity or adverse reactions. 3) "Circadian Pharmacology" or drugs targeting the circadian clock mechanism have been shown experimentally in rodent models to significantly reduce the damage due to heart attacks and prevent heart failure. Importantly, for rational translation of the most promising Circadian Medicine therapies to clinical practice, it is imperative that we understand how it helps treats disease in both biological sexes. 983:. Phytochrome A, phyA, is light labile and allows germination and de-etiolation when light is scarce. Phytochromes B–E are more stable with phyB, the main phytochrome in seedlings grown in the light. The cryptochrome (cry) gene is also a light-sensitive component of the circadian clock and is thought to be involved both as a photoreceptor and as part of the clock's endogenous pacemaker mechanism. Cryptochromes 1–2 (involved in blue–UVA) help to maintain the period length in the clock through a whole range of light conditions. 1169: 53: 1344: 1411:, the average human adult's temperature reaches its minimum at about 5:00 a.m., about two hours before habitual wake time. Baehr et al. found that, in young adults, the daily body temperature minimum occurred at about 04:00 (4 a.m.) for morning types, but at about 06:00 (6 a.m.) for evening types. This minimum occurred at approximately the middle of the eight-hour sleep period for morning types, but closer to waking in evening types. 1601: 1588: 9260: 1371:. Consistent with this research was a more recent study from 2010, which also identified sex differences, with the circadian period for women being slightly shorter (24.09 hours) than for men (24.19 hours). In this study, women tended to wake up earlier than men and exhibit a greater preference for morning activities than men, although the underlying biological mechanisms for these differences are unknown. 593: 1200:) gene. DBT protein causes phosphorylation and turnover of monomeric PER proteins. TIM is also phosphorylated by shaggy until sunset. After sunset, DBT disappears, so that PER molecules stably bind to TIM. PER/TIM dimer enters the nucleus several at night, and binds to CLK/CYC dimers. Bound PER completely stops the transcriptional activity of CLK and CYC. 1363:

from time cues (like clocks) and daylight, the researchers were not aware of the phase-delaying effects of indoor electric lights. The subjects were allowed to turn on light when they were awake and to turn it off when they wanted to sleep. Electric light in the evening delayed their circadian phase. A more stringent study conducted in 1999 by

727:), underscoring the conserved nature of the molecular circadian clock through evolution. Many more genetic components of the biological clock are now known. Their interactions result in an interlocked feedback loop of gene products resulting in periodic fluctuations that the cells of the body interpret as a specific time of the day. 1237: 416:(day); it may serve to imply that certain physiologic periods are close to 24 hours, if not exactly that length. Herein, "circadian" might be applied to all "24-hour" rhythms, whether or not their periods, individually or on the average, are different from 24 hours, longer or shorter, by a few minutes or hours. 636:. This is suggested by the maintenance (heritability) of circadian rhythms in fruit flies after several hundred generations in constant laboratory conditions, as well as in creatures in constant darkness in the wild, and by the experimental elimination of behavioral—but not physiological—circadian rhythms in 1479:

More-or-less independent circadian rhythms are found in many organs and cells in the body outside the suprachiasmatic nuclei (SCN), the "master clock". Indeed, neuroscientist Joseph Takahashi and colleagues stated in a 2013 article that "almost every cell in the body contains a circadian clock". For

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by photosynthesis repress PRR7. This repression of PRR7 then leads to the increased expression of CCA1. On the other hand, decreased photosynthetic sugar levels increase PRR7 expression and decrease CCA1 expression. This feedback loop between CCA1 and PRR7 is what is proposed to cause metabolic dawn.

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According to the metabolic dawn hypothesis, sugars produced by photosynthesis have potential to help regulate the circadian rhythm and certain photosynthetic and metabolic pathways. As the sun rises, more light becomes available, which normally allows more photosynthesis to occur. The sugars produced

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expression oscillates and peaks in the early evening. While it was previously hypothesised that these three genes model a negative feedback loop in which over-expressed CCA1 and LHY repress TOC1 and over-expressed TOC1 is a positive regulator of CCA1 and LHY, it was shown in 2012 by Andrew Millar and

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radiation during the daytime. As a result, replication was relegated to the dark. However, evidence for this is lacking: in fact the simplest organisms with a circadian rhythm, the cyanobacteria, do the opposite of this: they divide more in the daytime. Recent studies instead highlight the importance

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It is difficult to determine if a disturbance in the circadian rhythm is at fault for an increase in prevalence for substance abuse—or if other environmental factors such as stress are to blame. Changes to the circadian rhythm and sleep occur once an individual begins abusing drugs and alcohol. Once

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may be the more reliable marker. Benloucif et al. found that melatonin phase markers were more stable and more highly correlated with the timing of sleep than the core temperature minimum. They found that both sleep offset and melatonin offset are more strongly correlated with phase markers than the

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Early research into circadian rhythms suggested that most people preferred a day closer to 25 hours when isolated from external stimuli like daylight and timekeeping. However, this research was faulty because it failed to shield the participants from artificial light. Although subjects were shielded

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containing PAS domains, which facilitate protein-protein interactions; and several photoreceptors that fine-tune the clock to different light conditions. Anticipation of changes in the environment allows appropriate changes in a plant's physiological state, conferring an adaptive advantage. A better

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The rhythm persists in constant conditions, i.e. constant darkness, with a period of about 24 hours. The period of the rhythm in constant conditions is called the free-running period and is denoted by the Greek letter τ (tau). The rationale for this criterion is to distinguish circadian rhythms from

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Would local animals maintained under natural continuous daylight demonstrate the Aschoff effect described in previously published laboratory experiments using continuous light, in which rats' circadian activity patterns changed systematically to a longer period, expressing a 26-hour day of activity

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circadian rhythm to its environment could allow the plant to be better prepared for dawn and dusk, and thus be able to better synchronize its processes. In this study, it was also found that the genes that help to control chlorophyll peaked a few hours after dawn. This appears to be consistent with

1071:. LNKs binds to the 5'region of PRR5 and TOC1 and interacts with RNAP II and other transcription factors. Moreover, RVE8-LNKs interaction enables a permissive histone-methylation pattern (H3K4me3) to be modified and the histone-modification itself parallels the oscillation of clock gene expression. 833:

Free-running organisms that normally have one or two consolidated sleep episodes will still have them when in an environment shielded from external cues, but the rhythm is not entrained to the 24-hour light–dark cycle in nature. The sleep–wake rhythm may, in these circumstances, become out of phase

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Reduced cognitive function has been associated with circadian misalignment. Chronic shift workers display increased rates of operational error, impaired visual-motor performance and processing efficacy which can lead to both a reduction in performance and potential safety issues. Increased risk of

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Lighting requirements for circadian regulation are not simply the same as those for vision; planning of indoor lighting in offices and institutions is beginning to take this into account. Animal studies on the effects of light in laboratory conditions have until recently considered light intensity

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have profound consequences for circadian and metabolic events in the body. Animals that are forced to eat during their resting period show increased body mass and altered expression of clock and metabolic genes. In humans, shift work that favours irregular eating times is associated with altered

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cannot entrain to such abnormal day/night rhythms, this is referred to as a forced desynchrony protocol. Under such a protocol, sleep and wake episodes are uncoupled from the body's endogenous circadian period, which allows researchers to assess the effects of circadian phase (i.e., the relative

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with the 24-hour circadian cycle was grown in three different environments. One of these environments had a 20-hour light and dark cycle (10 hours of light and 10 hours of dark), the other had a 24-hour light and dark cycle (12 hours of light and 12 hours of dark),and the final environment had a

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Studies conducted on both animals and humans show major bidirectional relationships between the circadian system and abusive drugs. It is indicated that these abusive drugs affect the central circadian pacemaker. Individuals with substance use disorder display disrupted rhythms. These disrupted

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Due to the work nature of airline pilots, who often cross several time zones and regions of sunlight and darkness in one day, and spend many hours awake both day and night, they are often unable to maintain sleep patterns that correspond to the natural human circadian rhythm; this situation can

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Circadian rhythms allow organisms to anticipate and prepare for precise and regular environmental changes. They thus enable organisms to make better use of environmental resources (e.g. light and food) compared to those that cannot predict such availability. It has therefore been suggested that

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One of the first studies to determine how disruption of circadian rhythms causes cardiovascular disease was performed in the Tau hamsters, which have a genetic defect in their circadian clock mechanism. When maintained in a 24-hour light-dark cycle that was "out of sync" with their normal 22

1047:(Pseudo-Response Regulators.) The evening loop consists of GI (Gigantea) and ELF4, both involved in regulation of flowering time genes. When CCA1 and LHY are overexpressed (under constant light or dark conditions), plants become arrhythmic, and mRNA signals reduce, contributing to a 1470:

In contradiction to previous studies, it has been found that there is no effect of body temperature on performance on psychological tests. This is likely due to evolutionary pressures for higher cognitive function compared to the other areas of function examined in previous studies.

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What drove circadian rhythms to evolve has been an enigmatic question. Previous hypotheses emphasized that photosensitive proteins and circadian rhythms may have originated together in the earliest cells, with the purpose of protecting replicating DNA from high levels of damaging

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strictly maintain their circadian rhythms through 82 days and nights of sunshine. The researchers speculate that these two rodents notice that the apparent distance between the sun and the horizon is shortest once a day, and thus have a sufficient signal to entrain (adjust) by.

436:(day or 24 h). Note: term describes rhythms with an about 24-h cycle length, whether they are frequency-synchronized with (acceptable) or are desynchronized or free-running from the local environmental time scale, with periods of slightly yet consistently different from 24-h. 1808:

are associated with lifestyle and genetic factors. Among those factors, disruption of the circadian clockwork and/or misalignment of the circadian timing system with the external environment (e.g., light–dark cycle) can play a role in the development of metabolic disorders.

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circadian rhythm is through a transcription-translation feedback loop. The core clock mechanism consists of two interdependent feedback loops, namely the PER/TIM loop and the CLK/CYC loop. The CLK/CYC loop occurs during the day and initiates the transcription of the

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It has previously been found that matching a plant's circadian rhythm to its external environment's light and dark cycles has the potential to positively affect the plant. Researchers came to this conclusion by performing experiments on three different varieties of

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unless it has been tested and persists in conditions without external periodic input. In diurnal animals (active during daylight hours), in general τ is slightly greater than 24 hours, whereas, in nocturnal animals (active at night), in general τ is shorter than 24

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28-hour light and dark cycle (14 hours of light and 14 hours of dark). The two mutated plants were grown in both an environment that had a 20-hour light and dark cycle and in an environment that had a 28-hour light and dark cycle. It was found that the variety of

306:, and that this closes at night, but opens at sunrise, and by noon is completely unfolded; and at evening again it closes by degrees and remains shut at night, and the natives say that it goes to sleep." The tree mentioned by him was much later identified as the 1613:

The leading edge of circadian biology research is translation of basic body clock mechanisms into clinical tools, and this is especially relevant to the treatment of cardiovascular disease. Timing of medical treatment in coordination with the body clock,

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travels to the clock in the brain, and, through that, clocks in the rest of the body may be synchronized. This is how the timing of, for example, sleep/wake, body temperature, thirst, and appetite are coordinately controlled by the biological clock.

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Seizer L, Cornélissen-Guillaume G, Schiepek GK, Chamson E, Bliem HR and Schubert C (2022) About-Weekly Pattern in the Dynamic Complexity of a Healthy Subject's Cellular Immune Activity: A Biopsychosocial Analysis. Front. Psychiatry 13:799214. doi:

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of the brain to result in periodic release of hormones. The receptors for these hormones may be located far across the body and synchronize the peripheral clocks of various organs. Thus, the information of the time of the day as relayed by the

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When eyes receive light from the sun, the pineal gland's production of melatonin is inhibited, and the hormones produced keep the human awake. When the eyes do not receive light, melatonin is produced in the pineal gland and the human becomes

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The circadian rhythms of humans can be entrained to slightly shorter and longer periods than the Earth's 24 hours. Researchers at Harvard have shown that human subjects can at least be entrained to a 23.5-hour cycle and a 24.65-hour cycle.

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that are directly photosensitive, and project directly to the SCN, where they help in the entrainment (synchronization) of this master circadian clock. The proteins involved in the SCN clock are homologous to those found in the fruit fly.

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gene and its protein CRY causes the breakdown of TIM. Thus PER/TIM dimer dissociates, and the unbound PER becomes unstable. PER undergoes progressive phosphorylation and ultimately degradation. Absence of PER and TIM allows activation of

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Oritz-Tuldela E, Martinez-Nicolas A, Diaz-Mardomingo C, Garcia-Herranz S, Pereda-Perez I, Valencia A, Peraita H, Venero C, Madrid J, Rol M. 2014. The Characterization of Biological Rhythms in Mild Cognitive Impairment. BioMed Research

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Bennardo M, Alibhai F, Tsimakouridze E, Chinnappareddy N, Podobed P, Reitz C, et al. (December 2016). "Day-night dependence of gene expression and inflammatory responses in the remodeling murine heart post-myocardial infarction".

921:) to their overwintering grounds in central Mexico uses a time-compensated sun compass that depends upon a circadian clock in their antennae. Circadian rhythm is also known to control mating behavioral in certain moth species such as 565:

of all molecular processes in their cell(s). In order to keep track of time, the organism's circadian clock must maintain roughly a 24-hour periodicity despite the changing kinetics, a property known as temperature compensation. The

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Kosmadopoulos A, Sargent C, Darwent D, Zhou X, Dawson D, Roach GD (December 2014). "The effects of a split sleep-wake schedule on neurobehavioural performance and predictions of performance under conditions of forced desynchrony".

1161:) from the pupa, and the other during mating. The clock neurones are located in distinct clusters in the central brain. The best-understood clock neurones are the large and small lateral ventral neurons (l-LNvs and s-LNvs) of the 2822:

Reddy P, Zehring WA, Wheeler DA, Pirrotta V, Hadfield C, Hall JC, et al. (October 1984). "Molecular analysis of the period locus in Drosophila melanogaster and identification of a transcript involved in biological rhythms".

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Several studies have indicated that pineal melatonin feeds back on SCN rhythmicity to modulate circadian patterns of activity and other processes. However, the nature and system-level significance of this feedback are unknown.

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Proper KI, van de Langenberg D, Rodenburg W, Vermeulen RC, van der Beek AJ, van Steeg H, et al. (May 2016). "The Relationship Between Shift Work and Metabolic Risk Factors: A Systematic Review of Longitudinal Studies".

1081:. One of these varieties had a normal 24-hour circadian cycle. The other two varieties were mutated, one to have a circadian cycle of more than 27 hours, and one to have a shorter than normal circadian cycle of 20 hours. 1422:

can also be measured in morning urine. Both DLMO and the midpoint (in time) of the presence of the hormone in the blood or saliva have been used as circadian markers. However, newer research indicates that the melatonin

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Disruption to rhythms in the longer term is believed to have significant adverse health consequences for peripheral organs outside the brain, in particular in the development or exacerbation of cardiovascular disease.

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Nakano S, Uchida K, Kigoshi T, Azukizawa S, Iwasaki R, Kaneko M, et al. (August 1991). "Circadian rhythm of blood pressure in normotensive NIDDM subjects. Its relationship to microvascular complications".

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spiders are placed into chambers with periods of 19, 24, or 29 hours of evenly split light and dark, none of the spiders exhibited decreased longevity in their own circadian clock. These findings suggest that

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rhythms can increase the risk for substance abuse and relapse. It is possible that genetic and/or environmental disturbances to the normal sleep and wake cycle can increase the susceptibility to addiction.

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others that TOC1, in fact, serves as a repressor not only of CCA1, LHY, and PRR7 and 9 in the morning loop but also of GI and ELF4 in the evening loop. This finding and further computational modeling of

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showed such rhythms only in autumn and spring. The researchers suspect that other Arctic animals as well may not show circadian rhythms in the constant light of summer and the constant dark of winter.

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in isolated mollusk basal retinal neurons (BRNs). At the same time, different cells may communicate with each other resulting in a synchronized output of electrical signaling. These may interface with

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understanding of plant circadian rhythms has applications in agriculture, such as helping farmers stagger crop harvests to extend crop availability and securing against massive losses due to weather.

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In other words, they maintain circadian periodicity over a range of physiological temperatures. Many organisms live at a broad range of temperatures, and differences in thermal energy will affect the

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whose primary function is to rhythmically co-ordinate biological processes so they occur at the correct time to maximize the fitness of an individual. Circadian rhythms have been widely observed in

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For temperature studies, subjects must remain awake but calm and semi-reclined in near darkness while their rectal temperatures are taken continuously. Though variation is great among normal

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Martino TA, Oudit GY, Herzenberg AM, Tata N, Koletar MM, Kabir GM, et al. (May 2008). "Circadian rhythm disorganization produces profound cardiovascular and renal disease in hamsters".

1764:, a short period of sleep during the day, can reduce stress and may improve productivity without any measurable effect on normal circadian rhythms. Circadian rhythms also play a part in the 975:

Light is the signal by which plants synchronize their internal clocks to their environment and is sensed by a wide variety of photoreceptors. Red and blue light are absorbed through several

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was a circadian behaviour. He demonstrated that while temperature played a vital role in eclosion rhythm, the period of eclosion was delayed but not stopped when temperature was decreased.

360:, and Oskar Wahl conducted numerous experiments to determine whether this rhythm was attributable to an endogenous clock. The existence of circadian rhythm was independently discovered in 3252:

Jones CR, Campbell SS, Zone SE, Cooper F, DeSano A, Murphy PJ, et al. (September 1999). "Familial advanced sleep-phase syndrome: A short-period circadian rhythm variant in humans".

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The first human clock mutation was identified in an extended Utah family by Chris Jones, and genetically characterized by Ying-Hui Fu and Louis Ptacek. Affected individuals are extreme '

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conducted the first experiment designed to distinguish an endogenous clock from responses to daily stimuli. He noted that 24-hour patterns in the movement of the leaves of the plant

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Silvegren G, Löfstedt C, Qi Rosén W (March 2005). "Circadian mating activity and effect of pheromone pre-exposure on pheromone response rhythms in the moth Spodoptera littoralis".

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Wyatt JK, Ritz-De Cecco A, Czeisler CA, Dijk DJ (October 1999). "Circadian temperature and melatonin rhythms, sleep, and neurobehavioral function in humans living on a 20-h day".

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Sheeba V, Sharma VK, Chandrashekaran MK, Joshi A (September 1999). "Persistence of eclosion rhythm in Drosophila melanogaster after 600 generations in an aperiodic environment".

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The central oscillator generates a self-sustaining rhythm and is driven by two interacting feedback loops that are active at different times of day. The morning loop consists of

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activity, and fragrance emission, among others. Circadian rhythms occur as a plant entrains to synchronize with the light cycle of its surrounding environment. These rhythms are

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Czeisler CA, Duffy JF, Shanahan TL, Brown EN, Mitchell JF, Rimmer DW, et al. (June 1999). "Stability, precision, and near-24-hour period of the human circadian pacemaker".

8795:"Circadian genes in a blind subterranean mammal II: conservation and uniqueness of the three Period homologs in the blind subterranean mole rat, Spalax ehrenbergi superspecies" 4769:

Dodd AN, Salathia N, Hall A, Kévei E, Tóth R, Nagy F, et al. (July 2005). "Plant circadian clocks increase photosynthesis, growth, survival, and competitive advantage".

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Grote L, Mayer J, Penzel T, Cassel W, Krzyzanek E, Peter JH, et al. (1994). "Nocturnal hypertension and cardiovascular risk: consequences for diagnosis and treatment".

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Guyomarc'h C, Lumineau S, Richard JP (May 1998). "Circadian rhythm of activity in Japanese quail in constant darkness: variability of clarity and possibility of selection".

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In 2018, researchers found that the expression of PRR5 and TOC1 hnRNA nascent transcripts follows the same oscillatory pattern as processed mRNA transcripts rhythmically in

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Grima B, Lamouroux A, Chélot E, Papin C, Limbourg-Bouchon B, Rouyer F (November 2002). "The F-box protein slimb controls the levels of clock proteins period and timeless".

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Plant circadian rhythms tell the plant what season it is and when to flower for the best chance of attracting pollinators. Behaviors showing rhythms include leaf movement (

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Studies have shown that maintaining normal sleep and circadian rhythms is important for many aspects of brain and health. A number of studies have also indicated that a

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environment." In a study of young men, it was found that the heart rate reaches its lowest average rate during sleep, and its highest average rate shortly after waking.

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Toh KL, Jones CR, He Y, Eide EJ, Hinz WA, Virshup DM, et al. (February 2001). "An hPer2 phosphorylation site mutation in familial advanced sleep phase syndrome".

803:. However, it is not clear whether there is a strong association between clock gene polymorphisms in humans and the susceptibility to develop the metabolic syndrome. 819:

period, is shorter or longer than 24 hours. The environmental cues that reset the rhythms each day are called zeitgebers. Totally blind subterranean mammals (e.g.,

475:, and that the gene covers 7.1-kilobase (kb) interval on the X chromosome and encodes a 4.5-kb poly(A)+ RNA. They went on to discover the key genes and neurones in 4084:"The Rhythms of Life: The Biological Clocks That Control the Daily Lives of Every Living Thing" Russell Foster & Leon Kreitzman, Publisher: Profile Books Ltd. 752:

Circadian rhythmicity is present in the sleeping and feeding patterns of animals, including human beings. There are also clear patterns of core body temperature,

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Leloup JC, Goldbeter A (February 1998). "A model for circadian rhythms in Drosophila incorporating the formation of a complex between the PER and TIM proteins".

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with a 24-hour circadian rhythm cycle grew best in an environment that also had a 24-hour light and dark cycle. Overall, it was found that all the varieties of

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Introducing Biological Rhythms: A Primer on the Temporal Organization of Life, with Implications for Health, Society, Reproduction, and the Natural Environment

1276:. Destruction of the SCN results in the complete absence of a regular sleep–wake rhythm. The SCN receives information about illumination through the eyes. The 628:

circadian rhythms put organisms at a selective advantage in evolutionary terms. However, rhythmicity appears to be as important in regulating and coordinating

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Alibhai FJ, Tsimakouridze EV, Reitz CJ, Pyle WG, Martino TA (July 2015). "Consequences of Circadian and Sleep Disturbances for the Cardiovascular System".

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Martino T, Arab S, Straume M, Belsham DD, Tata N, Cai F, et al. (April 2004). "Day/night rhythms in gene expression of the normal murine heart".

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Zelinski EL, Deibel SH, McDonald RJ (March 2014). "The trouble with circadian clock dysfunction: multiple deleterious effects on the brain and body".

169:, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism (i.e., 1688:

The stabilization of sleep and the circadian rhythm might possibly help to reduce the vulnerability to addiction and reduce the chances of relapse.

8848:"Environmental Circadian Disruption Worsens Neurologic Impairment and Inhibits Hippocampal Neurogenesis in Adult Rats After Traumatic Brain Injury" 4703:"Targeted Recruitment of the Basal Transcriptional Machinery by LNK Clock Components Controls the Circadian Rhythms of Nascent RNAs in Arabidopsis" 1165:. These neurones produce pigment dispersing factor (PDF), a neuropeptide that acts as a circadian neuromodulator between different clock neurones. 349:

showed that animals are capable of maintaining 24-hour activity patterns in the absence of external cues such as light and changes in temperature.

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cites this as contributing to many accidents, and has conducted several research studies in order to find methods of combating fatigue in pilots.

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onset of sleep. In addition, the declining phase of the melatonin levels is more reliable and stable than the termination of melatonin synthesis.

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The rhythm is linked to the light–dark cycle. Animals, including humans, kept in total darkness for extended periods eventually function with a

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does not lead to a behavioral phenotype (the animals still have normal circadian rhythms), which questions its importance in rhythm generation.

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is unique in that its locomotor and web-building activity cause it to have an exceptionally short-period circadian clock, about 19 hours. When

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genes in mice have demonstrated the importance of body clocks to ensure the proper timing of cellular/metabolic events; clock-mutant mice are

661:(ROS) in the presence of daylight are likely to have driven a need to evolve circadian rhythms to preempt, and therefore counteract, damaging 365: 6979:"SR9009 administered for one day after myocardial ischemia-reperfusion prevents heart failure in mice by targeting the cardiac inflammasome" 826:

sp.) are able to maintain their endogenous clocks in the apparent absence of external stimuli. Although they lack image-forming eyes, their

7360: 6558: 5987:"Individual differences in the phase and amplitude of the human circadian temperature rhythm: with an emphasis on morningness-eveningness" 4157: 9206: 5232:

Ko HW, Jiang J, Edery I (December 2002). "Role for Slimb in the degradation of Drosophila Period protein phosphorylated by Doubletime".

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generated, self-sustaining and are relatively constant over a range of ambient temperatures. Important features include two interacting

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It is now known that the molecular circadian clock can function within a single cell. That is, it is cell-autonomous. This was shown by

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dementia is associated with chronic night shift workers compared to day shift workers, particularly for individuals over 50 years old.

1308:, leading to the SCN. If cells from the SCN are removed and cultured, they maintain their own rhythm in the absence of external cues. 1023:, peaking before lights-off (36h, 60h, etc.). The timeseries show 24-hour, circadian rhythms of gene expression in the living plants. 657:

approximately 2.3 billion years ago. The current view is that circadian changes in environmental oxygen levels and the production of

6418:"Restricted feeding uncouples circadian oscillators in peripheral tissues from the central pacemaker in the suprachiasmatic nucleus" 2236: 323:

Mnemonic Rhyme to Aid in the Selection of Acu-points According to the Diurnal Cycle, the Day of the Month and the Season of the Year

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Various studies on humans have made use of enforced sleep/wake cycles strongly different from 24 hours, such as those conducted by

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driven by the promoter sequences of clock genes. The signals of seedlings 61 (red) and 62 (blue) reflect transcription of the gene

8081:"The human endogenous circadian system causes greatest platelet activation during the biological morning independent of behaviors" 1507:

Though oscillators in the skin respond to light, a systemic influence has not been proven. In addition, many oscillators, such as

1504:, and skin. There is also some evidence that the olfactory bulb and prostate may experience oscillations, at least when cultured. 881:) show circadian rhythms only in the parts of the year that have daily sunrises and sunsets. In one study of reindeer, animals at 3641:"Circadian gene expression in individual fibroblasts: cell-autonomous and self-sustained oscillators pass time to daughter cells" 1768:, which is crucial for maintaining a state of consciousness. A reversal in the sleep–wake cycle may be a sign or complication of 964: 6627:

Wright KP, Hull JT, Czeisler CA (December 2002). "Relationship between alertness, performance, and body temperature in humans".

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Rea MS, Figueiro M, Bullough J (May 2002). "Circadian photobiology: an emerging framework for lighting practice and research".

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Leso V, Caturano A, Vetrani I, Iavicoli I (January 2021). "Shift or night shift work and dementia risk: a systematic review".

3441:"Formal properties of the circadian and photoperiodic systems of Japanese quail: phase response curve and effects of T-cycles" 9158: 8939: 7790: 6568: 4185:

Folk GE, Thrift DL, Zimmerman MB, Reimann P (2006-12-01). "Mammalian activity – rest rhythms in Arctic continuous daylight".

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Veleri S, Wülbeck C (May 2004). "Unique self-sustaining circadian oscillators within the brain of Drosophila melanogaster".

2237:"Enquiry into plants and minor works on odours and weather signs, with an English translation by Sir Arthur Hort, bart 1916" 702:) of their central oscillator. This clock has been shown to sustain a 22-hour rhythm over several days upon the addition of 227:; diurnal rhythms should not be called circadian rhythms unless they can be confirmed as endogenous, and not environmental. 9416: 1615: 854: 3786:"The internal circadian clock increases hunger and appetite in the evening independent of food intake and other behaviors" 2907:

Bargiello TA, Jackson FR, Young MW (1984). "Restoration of circadian behavioural rhythms by gene transfer in Drosophila".

1327:. Secretion of melatonin peaks at night and ebbs during the day and its presence provides information about night-length. 1311:

The SCN takes the information on the lengths of the day and night from the retina, interprets it, and passes it on to the

1157:, and they act together with the clock neurones. There are two unique rhythms, one during the process of hatching (called 463:

gene was isolated in 1984 by two teams of researchers. Konopka, Jeffrey Hall, Michael Roshbash and their team showed that

1903: 302:. In his book, 'Περὶ φυτῶν ἱστορία', or 'Enquiry into plants', Theophrastus describes a "tree with many leaves like the 9175: 1008:

under three cycles of 12h light: 12h dark followed by 3 days of constant light (from 96h). Their genomes carry firefly

329: 1636:) but not color, which can be shown to "act as an essential regulator of biological timing in more natural settings". 1956: 1781: 1520: 578:

coefficient remains approximately 1 as temperature increases, the rhythm is considered to be temperature-compensated.

7371: 6377:"Low-dose ultraviolet B rays alter the mRNA expression of the circadian clock genes in cultured human keratinocytes" 551:

illustrates the ability of the human biological clock to adjust to the local time; a person will usually experience

4173:...så det ikke ut til at reinen hadde noen døgnrytme om sommeren. Svalbardreinen hadde det heller ikke om vinteren. 2868:"P-element transformation with period locus DNA restores rhythmicity to mutant, arrhythmic Drosophila melanogaster" 1887: 8194:"Metabolic and cardiovascular consequences of shift work: The role of circadian disruption and sleep disturbances" 7289:"The Dangers of LED-Blue light-The Suppression of Melatonin-Resulting in-Insomnia-And Cancers | Robert Hardt" 6045:"NHLBI Workshop: "Circadian Clock at the Interface of Lung Health and Disease" 28-29 April 2014 Executive Summary" 4831:"Interactions between circadian clocks and photosynthesis for the temporal and spatial coordination of metabolism" 9199: 8544:"Relationship between shift work, night work, and subsequent dementia: A systematic evaluation and meta-analysis" 6048: 5587:

Pfeffer M, Korf HW, Wicht H (March 2018). "Synchronizing effects of melatonin on diurnal and circadian rhythms".

1717: 275: 849:

environments, as systems that mimic the light–dark cycle have been found to be highly beneficial to astronauts.

5889:"Stability of melatonin and temperature as circadian phase markers and their relation to sleep times in humans" 1529:(PRC). Depending on the timing, light can advance or delay the circadian rhythm. Both the PRC and the required 1652: 230:

Although circadian rhythms are endogenous, they are adjusted to the local environment by external cues called

8656: 7154:"Circadian rhythms influence cardiovascular disease differently in males and females: role of sex and gender" 3842: 1893: 995: 567: 33: 8284: 7726:"Benefits of napping in healthy adults: impact of nap length, time of day, age, and experience with napping" 1856:

Circadian rhythms was taken as an example of scientific knowledge being transferred into the public sphere.

1722:

Disruption to rhythms usually has a negative effect. Many travelers have experienced the condition known as

5403:

Goldbeter A (September 1995). "A model for circadian oscillations in the Drosophila period protein (PER)".

1980: 1898: 1750: 1293: 1060:

functions and interactions suggest a reframing of the plant circadian clock as a triple negative-component

1016: 7446:"Assessing ethanol's actions in the suprachiasmatic circadian clock using in vivo and in vitro approaches" 3835:"Clock Tutorial #16: Photoperiodism – Models and Experimental Approaches (original work from 2005-08-13)" 2628:

Halberg F, Cornélissen G, Katinas G, Syutkina EV, Sothern RB, Zaslavskaya R, et al. (October 2003).

1882: 1765: 1128: 673: 540: 314: 174: 37: 8742:"Biological clock in total darkness: the Clock/MOP3 circadian system of the blind subterranean mole rat" 5938:"Diurnal cortisol slopes and mental and physical health outcomes: A systematic review and meta-analysis" 815:

rhythm. Their sleep cycle is pushed back or forward each "day", depending on whether their "day", their

9192: 2418: 2007: 3971:"The nuclear receptor REV-ERBα is required for the daily balance of carbohydrate and lipid metabolism" 3922:"The nuclear receptor REV-ERBα is required for the daily balance of carbohydrate and lipid metabolism" 9406: 6641: 1961: 1456: 1044: 17: 2362:"Timing and consolidation of human sleep, wakefulness, and performance by a symphony of oscillators" 310:

tree by the botanist, H Bretzl, in his book on the botanical findings of the Alexandrian campaigns.

9421: 7067:

Alibhai FJ, LaMarre J, Reitz CJ, Tsimakouridze EV, Kroetsch JT, Bolz SS, et al. (April 2017).

5516: 4548:"Distinct roles of GIGANTEA in promoting flowering and regulating circadian rhythms in Arabidopsis" 3969:

Delezie J, Dumont S, Dardente H, Oudart H, Gréchez-Cassiau A, Klosen P, et al. (August 2012).

3920:

Delezie J, Dumont S, Dardente H, Oudart H, Gréchez-Cassiau A, Klosen P, et al. (August 2012).

3015: 1305: 1192:

genes. But their proteins levels remain low until dusk, because during daylight also activates the

1064:

model rather than the positive/negative-element feedback loop characterizing the clock in mammals.

539:

The rhythm can be reset by exposure to external stimuli (such as light and heat), a process called

389: 250: 4130: 3054:

Vitaterna MH, King DP, Chang AM, Kornhauser JM, Lowrey PL, McDonald JD, et al. (April 1994).

2866:

Zehring WA, Wheeler DA, Reddy P, Konopka RJ, Kyriacou CP, Rosbash M, et al. (December 1984).

9385: 9370: 1696: 1357: 1265: 1249: 1162: 1101:

and increased growth in environments whose light and dark cycles matched their circadian rhythm.

991: 682: 658: 471:

stops circadian activity. At the same time, Michael W. Young's team reported similar effects of

361: 352:

In the early 20th century, circadian rhythms were noticed in the rhythmic feeding times of bees.

6893:

Aziz IS, McMahon AM, Friedman D, Rabinovich-Nikitin I, Kirshenbaum LA, Martino TA (April 2021).

4020:"Association between polymorphisms in the Clock gene, obesity and the metabolic syndrome in man" 1414:

Melatonin is absent from the system or undetectably low during daytime. Its onset in dim light,

866: 8389:"The effects of shift work on body weight change - a systematic review of longitudinal studies" 7026:

Alibhai FJ, Reitz CJ, Peppler WT, Basu P, Sheppard P, Choleris E, et al. (February 2018).

6636: 5130:

Boothroyd CE, Young MW (2008). "The in(put)s and out(put)s of the Drosophila circadian clock".

4654:"The clock gene circuit in Arabidopsis includes a repressilator with additional feedback loops" 4234:"Antennal circadian clocks coordinate sun compass orientation in migratory monarch butterflies" 4161: 1651:, which is white light, suppresses melatonin at a rate more than three times greater than HPS. 1393: 1367:

estimated the natural human rhythm to be closer to 24 hours and 11 minutes: much closer to the

885:

showed circadian rhythms in the autumn, winter and spring, but not in the summer. Reindeer on

703: 428:

Circadian: relating to biologic variations or rhythms with a frequency of 1 cycle in 24 ± 4 h;

291: 6674:"Sleep, wake and phase dependent changes in neurobehavioral function under forced desynchrony" 6672:

Zhou X, Ferguson SA, Matthews RW, Sargent C, Darwent D, Kennaway DJ, et al. (July 2011).

5823:

Duffy JF, Cain SW, Chang AM, Phillips AJ, Münch MY, Gronfier C, et al. (September 2011).

1224:

This protein model was developed based on the oscillations of the PER and TIM proteins in the

7493: 7028:"Female ClockΔ19/Δ19 mice are protected from the development of age-dependent cardiomyopathy" 6375:

Kawara S, Mydlarski R, Mamelak AJ, Freed I, Wang B, Watanabe H, et al. (December 2002).

5796: 2097:

Young MW, Kay SA (September 2001). "Time zones: a comparative genetics of circadian clocks".

1685:

an individual stops using drugs and alcohol, the circadian rhythm continues to be disrupted.

1133: 1005: 923: 710:

circadian timekeeper were dependent upon a DNA transcription/translation feedback mechanism.

654: 607: 8193: 8079:

Scheer FA, Michelson AD, Frelinger AL, Evoniuk H, Kelly EE, McCarthy M, et al. (2011).

7069:"Disrupting the key circadian regulator CLOCK leads to age-dependent cardiovascular disease" 1480:

example, these clocks, called peripheral oscillators, have been found in the adrenal gland,

9306: 9107: 9066: 8962: 8902: 8806: 8753: 8449: 8296: 8092: 6205: 5836: 5657: 5466: 5412: 5241: 5190: 5139: 4953: 4893: 4778: 4608: 4502: 4341: 4245: 4194: 4060: 3876: 3701: 3362: 3210: 3067: 2971: 2916: 2776: 2582: 2193: 2053: 1925: 1526: 1077: 1019:, peaking after lights-on (48h, 72h, etc.). Seedlings 64 (pale grey) and 65 (teal) reflect 1000: 939: 6805:"Influence of the cardiomyocyte circadian clock on cardiac physiology and pathophysiology" 6416:

Damiola F, Le Minh N, Preitner N, Kornmann B, Fleury-Olela F, Schibler U (December 2000).

6072:"Quantitative analysis of the 24-hour blood pressure and heart rate patterns in young men" 5825:"Sex difference in the near-24-hour intrinsic period of the human circadian timing system" 5555: 4546:

Mizoguchi T, Wright L, Fujiwara S, Cremer F, Lee K, Onouchi H, et al. (August 2005).

2571:"On Temperature Independence in the Clock System Controlling Emergence Time in Drosophila" 2526:

Pittendrigh CS (1993). "Temporal organization: reflections of a Darwinian clock-watcher".

1591:

How humans can optimize their circadian rhythm in terms of ability to achieve proper sleep

197:

and there is evidence that they evolved independently in each of these kingdoms of life.

8: 8634: 8630:"Nobel in physiology, medicine awarded to three Americans for discovery of 'clock genes'" 7236:

Walmsley L, Hanna L, Mouland J, Martial F, West A, Smedley AR, et al. (April 2015).

5703:

Duffy JF, Wright KP (August 2005). "Entrainment of the human circadian system by light".

2240: 1777: 1533:

vary from species to species, and lower light levels are required to reset the clocks in

1051:

loop. Gene expression of CCA1 and LHY oscillates and peaks in the early morning, whereas

890: 882: 776: 299: 9111: 9070: 8966: 8889:

Ditty JL, Williams SB, Golden SS (2003). "A cyanobacterial circadian timing mechanism".

8810: 8757: 8453: 8300: 8096: 6209: 6151: 5840: 5661: 5470: 5416: 5245: 5194: 5143: 4957: 4897: 4782: 4652:

Pokhilko A, Fernández AP, Edwards KD, Southern MM, Halliday KJ, Millar AJ (March 2012).

4612: 4506: 4345: 4249: 4198: 3880: 3705: 3543:

Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences

3366: 3214: 3071: 2975: 2920: 2780: 2586: 2539: 2197: 2057: 1753:(DSPD), are associated with irregular or pathological functioning of circadian rhythms. 1584:

do not have the same costs of extreme desynchronization as do other species of animals.

1418:(DLMO), at roughly 21:00 (9 p.m.) can be measured in the blood or the saliva. Its major 1149:

The molecular mechanism of circadian rhythm and light perception are best understood in

606:

Please expand the section to include this information. Further details may exist on the

9339: 9296: 9147: 9133: 9036: 8928: 8914: 8872: 8847: 8709: 8570: 8543: 8519: 8494: 8470: 8437: 8418: 8364: 8339: 8320: 8221: 8169: 8115: 8080: 8056: 8029: 8010: 7959: 7932: 7913: 7864: 7837: 7782: 7755: 7701: 7674: 7645: 7592: 7567: 7543: 7518: 7470: 7445: 7421: 7396: 7338: 7313: 7264: 7237: 7218: 7183: 7134: 7003: 6978: 6924: 6834: 6747: 6698: 6673: 6609: 6539: 6491: 6466: 6352: 6327: 6303: 6278: 6228: 6193: 6160: 6135: 6016: 5962: 5937: 5918: 5859: 5824: 5772: 5747: 5728: 5680: 5645: 5564: 5539: 5490: 5436: 5385: 5314: 5265: 5214: 5163: 5107: 5082: 5063: 4974: 4941: 4914: 4881: 4857: 4830: 4802: 4727: 4702: 4678: 4653: 4629: 4596: 4572: 4547: 4523: 4490: 4466: 4441: 4417: 4401: 4314: 4266: 4233: 4210: 4094:

Regestein QR, Pavlova M (September 1995). "Treatment of delayed sleep phase syndrome".

4000: 3951: 3897: 3864: 3810: 3785: 3766: 3670: 3616: 3587: 3563: 3538: 3470: 3386: 3335: 3277: 3234: 3142: 3088: 3055: 2940: 2848: 2551: 2505: 2465: 2440: 2391: 2337: 2312: 2217: 2158: 2141: 2122: 2074: 2041: 2001: 1727: 1665: 1546: 1511:, for example, have been shown to respond to inputs other than light, such as feeding. 1379:

The classic phase markers for measuring the timing of a mammal's circadian rhythm are:

1364: 1281: 827: 812: 753: 345:, sleepiness increases and decreases with a period of approximately 24 hours. In 1918, 170: 8985: 8950: 8829: 8794: 8510: 8156: 8139: 6977:

Reitz CJ, Alibhai FJ, Khatua TN, Rasouli M, Bridle BW, Burris TP, et al. (2019).

6442: 6417: 6112: 5936:

Adam EK, Quinn ME, Tavernier R, McQuillan MT, Dahlke KA, Gilbert KE (September 2017).

5887:

Benloucif S, Guico MJ, Reid KJ, Wolfe LF, L'hermite-Balériaux M, Zee PC (April 2005).

2992: 2959: 2799: 2764: 2656: 2629: 2605: 2570: 1703:. Moreover, genetic manipulations of clock genes profoundly affect cocaine's actions. 1655:

from long term nighttime light exposure can be undone by returning to a normal cycle.

1241: 9215: 9154: 9125: 9082: 9028: 8990: 8935: 8906: 8877: 8834: 8781: 8776: 8741: 8701: 8610: 8575: 8524: 8475: 8410: 8369: 8312: 8308: 8262: 8213: 8161: 8120: 8061: 8002: 7964: 7905: 7869: 7796: 7786: 7747: 7742: 7725: 7706: 7637: 7597: 7548: 7475: 7426: 7343: 7269: 7222: 7175: 7126: 7090: 7049: 7008: 6959: 6955: 6928: 6916: 6875: 6826: 6785: 6739: 6703: 6654: 6601: 6597: 6564: 6531: 6496: 6447: 6398: 6393: 6376: 6357: 6308: 6233: 6165: 6093: 6008: 6003: 5986: 5967: 5910: 5864: 5777: 5720: 5685: 5604: 5569: 5482: 5428: 5377: 5333: 5306: 5301: 5284: 5257: 5206: 5155: 5112: 5055: 5020: 5015: 4998: 4979: 4919: 4862: 4794: 4732: 4683: 4634: 4577: 4528: 4471: 4409: 4396: 4379: 4357: 4318: 4306: 4271: 4111: 4107: 4041: 3992: 3943: 3902: 3863:

Turek FW, Joshu C, Kohsaka A, Lin E, Ivanova G, McDearmon E, et al. (May 2005).

3815: 3758: 3717: 3662: 3621: 3568: 3539:"Evolution of time-keeping mechanisms: early emergence and adaptation to photoperiod" 3519: 3514: 3489: 3462: 3421: 3378: 3327: 3269: 3226: 3183: 3134: 3093: 2997: 2932: 2889: 2884: 2867: 2840: 2836: 2804: 2745: 2716: 2691: 2661: 2610: 2543: 2488:

Bruce VG, Pittendrigh CS (1957). "Endogenous Rhythms in Insects and Microorganisms".

2470: 2456: 2383: 2342: 2276: 2209: 2163: 2114: 2079: 1648: 1644: 1571: 1448: 1292:"), which are used for conventional vision. But the retina also contains specialized 1048: 914: 846: 562: 555:

before entrainment of their circadian clock has brought it into sync with local time.

520:

To be called circadian, a biological rhythm must meet these three general criteria:

376: 342: 240: 8918: 8422: 8324: 8225: 8173: 8014: 7917: 7759: 7633: 7187: 7138: 6838: 6751: 6113:"The effect of the circadian rhythm of body temperature on A-level exam performance" 5922: 5732: 5389: 5318: 5067: 4806: 4421: 4214: 4004: 3955: 3770: 3674: 3505: 3474: 3390: 3339: 3281: 3146: 2555: 2509: 2395: 2221: 2126: 9239: 9234: 9137: 9115: 9096:"No transcription-translation feedback in circadian rhythm of KaiC phosphorylation" 9074: 9020: 8980: 8970: 8898: 8867: 8859: 8824: 8814: 8771: 8761: 8713: 8691: 8602: 8565: 8555: 8514: 8506: 8465: 8457: 8400: 8359: 8351: 8304: 8254: 8205: 8151: 8110: 8100: 8051: 8041: 7994: 7954: 7944: 7897: 7859: 7849: 7778: 7737: 7696: 7686: 7649: 7629: 7587: 7579: 7538: 7530: 7465: 7457: 7416: 7408: 7333: 7325: 7259: 7249: 7210: 7165: 7118: 7080: 7039: 6998: 6990: 6951: 6906: 6865: 6816: 6777: 6731: 6693: 6685: 6646: 6613: 6593: 6543: 6523: 6486: 6478: 6437: 6429: 6388: 6347: 6339: 6298: 6290: 6277:

Abraham U, Granada AE, Westermark PO, Heine M, Kramer A, Herzel H (November 2010).

6223: 6213: 6155: 6147: 6083: 6020: 5998: 5957: 5953: 5949: 5900: 5854: 5844: 5767: 5759: 5712: 5675: 5665: 5596: 5559: 5551: 5474: 5440: 5420: 5369: 5296: 5269: 5249: 5218: 5198: 5167: 5147: 5102: 5094: 5047: 5010: 4999:"PRR7 protein levels are regulated by light and the circadian clock in Arabidopsis" 4969: 4961: 4909: 4901: 4852: 4842: 4786: 4722: 4714: 4673: 4665: 4624: 4616: 4567: 4559: 4518: 4510: 4461: 4453: 4391: 4353: 4349: 4298: 4261: 4253: 4202: 4103: 4031: 3982: 3933: 3892: 3884: 3805: 3797: 3748: 3709: 3652: 3611: 3603: 3558: 3550: 3509: 3501: 3452: 3413: 3370: 3319: 3261: 3238: 3218: 3173: 3124: 3083: 3075: 2987: 2979: 2944: 2924: 2879: 2832: 2794: 2784: 2651: 2641: 2600: 2590: 2535: 2497: 2460: 2452: 2373: 2332: 2324: 2201: 2153: 2106: 2069: 2061: 2040:

Edgar RS, Green EW, Zhao Y, van Ooijen G, Olmedo M, Qin X, et al. (May 2012).

2017: 2012: 1986: 1915: 1842: 1742: 1554: 1436: 839: 525:

The rhythm has an endogenous free-running period that lasts approximately 24 hours.

486: 274:

cycles. In clinical settings, an abnormal circadian rhythm in humans is known as a

130: 71: 9040: 7987:

American Journal of Physiology. Regulatory, Integrative and Comparative Physiology

7461: 7111:

American Journal of Physiology. Regulatory, Integrative and Comparative Physiology

6629:

American Journal of Physiology. Regulatory, Integrative and Comparative Physiology

6527: 6343: 5494: 5098: 3056:"Mutagenesis and mapping of a mouse gene, Clock, essential for circadian behavior" 2852: 1853:"for their discoveries of molecular mechanisms controlling the circadian rhythm". 1244:

illustrating the influence of light and darkness on circadian rhythms and related

369: 9375: 8606: 8258: 8105: 7378: 7372:

https://www.faa.gov/pilots/safety/pilotsafetybrochures/media/Circadian_Rhythm.pdf

7254: 7170: 7153: 6735: 6218: 5763: 5670: 3178: 3161: 3129: 3112: 2710: 1996: 1846: 1838: 1558: 1440: 1257: 952: 897: 830:(which detect light) are still functional; they do surface periodically as well. 735: 669: 357: 235: 178: 7085: 7068: 5600: 4491:"Molecular mechanisms underlying phytochrome-controlled morphogenesis in plants" 3607: 3111:

Debruyne JP, Noton E, Lambert CM, Maywood ES, Weaver DR, Reppert SM (May 2006).

459:) gene, the first discovered genetic determinant of behavioral rhythmicity. The 9411: 9380: 9318: 8955: