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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 principle circadian pacemaker in mammals and is necessary for generating circadian rhythms. Reception of light inputs from photosensitive retinal ganglion cells allow the SCN 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.
A circadian clock, or circadian oscillator, is a biochemical oscillator that cycles with a stable phase and is synchronized with solar time.
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.
Gene David Block is an American biologist who has served as the current and 6th chancellor of the University of California, Los Angeles since August 2007.
CLOCK is a gene encoding a basic helix-loop-helix-PAS transcription factor that is known to affect both the persistence and period of circadian rhythms.
Jürgen Walther Ludwig Aschoff was a German physician, biologist and behavioral physiologist. Together with Erwin Bünning and Colin Pittendrigh, he is considered to be a co-founder of the field of chronobiology.
Joseph S. Takahashi is a Japanese American neurobiologist and geneticist. Takahashi is a professor at University of Texas Southwestern Medical Center as well as an investigator at the Howard Hughes Medical Institute. Takahashi's research group discovered the genetic basis for the mammalian circadian clock in 1994 and identified the Clock gene in 1997. Takahashi was elected to the National Academy of Sciences in 2003.
Russell Grant Foster, CBE, FRS FMedSci is a British professor of circadian neuroscience, the Director of the Nuffield Laboratory of Ophthalmology and the Head of the Sleep and Circadian Neuroscience Institute (SCNi). He is also a Nicholas Kurti Senior Fellow at Brasenose College at the University of Oxford. Foster and his group are credited with key contributions to the discovery of the non-rod, non-cone, photosensitive retinal ganglion cells (pRGCs) in the mammalian retina which provide input to the circadian rhythm system. He has written and co-authored over a hundred scientific publications.
Michael Morris Rosbash is an American geneticist and chronobiologist. Rosbash is a professor and researcher at Brandeis University and investigator at the Howard Hughes Medical Institute. Rosbash's research group cloned the Drosophila period gene in 1984 and proposed the Transcription Translation Negative Feedback Loop for circadian clocks in 1990. In 1998, they discovered the cycle gene, clock gene, and cryptochrome photoreceptor in Drosophila through the use of forward genetics, by first identifying the phenotype of a mutant and then determining the genetics behind the mutation. Rosbash was elected to the National Academy of Sciences in 2003. Along with Michael W. Young and Jeffrey C. Hall, he was awarded the 2017 Nobel Prize in Physiology or Medicine "for their discoveries of molecular mechanisms controlling the circadian rhythm".
Michael Warren Young is an American biologist and geneticist. He has dedicated over three decades to research studying genetically controlled patterns of sleep and wakefulness within Drosophila melanogaster.
John B. Hogenesch is an American chronobiologist and Professor of Pediatrics at the Cincinnati Children's Hospital Medical Center. The primary focus of his work has been studying the network of mammalian clock genes from the genomic and computational perspective to further the understanding of circadian behavior. He is currently the Deputy Director of the Center for Chronobiology, an Ohio Eminent Scholar, and Professor of Pediatrics in the Divisions of Perinatal Biology and Immunobiology at the Cincinnati Children's Hospital Medical Center.
Douglas G. McMahon is a professor of Biological Sciences and Pharmacology at Vanderbilt University. McMahon has contributed several important discoveries to the field of chronobiology and vision. His research focuses on connecting the anatomical location in the brain to specific behaviors. As a graduate student under Gene Block, McMahon identified that the basal retinal neurons (BRNs) of the molluscan eye exhibited circadian rhythms in spike frequency and membrane potential, indicating they are the clock neurons. He became the 1986 winner of the Society for Neuroscience's Donald B. Lindsley Prize in Behavioral Neuroscience for his work. Later, he moved on to investigate visual, circadian, and serotonergic mechanisms of neuroplasticity. In addition, he helped find that constant light can desynchronize the circadian cells in the suprachiasmatic nucleus (SCN). He has always been interested in the underlying causes of behavior and examining the long term changes in behavior and physiology in the neurological modular system. McMahon helped identifying a retrograde neurotransmission system in the retina involving the melanopsin containing ganglion cells and the retinal dopaminergic amacrine neurons.
Steve A. Kay is a British-born chronobiologist who mainly works in the United States. Dr. Kay has pioneered methods to monitor daily gene expression in real time and characterized circadian gene expression in plants, flies and mammals. In 2014, Steve Kay celebrated 25 years of successful chronobiology research at the Kaylab 25 Symposium, joined by over one hundred researchers with whom he had collaborated with or mentored. Dr. Kay, a member of the National Academy of Sciences, U.S.A., briefly served as president of The Scripps Research Institute. and is currently a professor at the University of Southern California. He also served on the Life Sciences jury for the Infosys Prize in 2011.
William Joseph Schwartz is an American neurologist and scientist who serves as Professor and Associate Chair for Research and Education in the neurology department at the University of Texas Dell Medical School. His work on the neurobiology of circadian timekeeping has focused on the mammalian suprachiasmatic nucleus. Schwartz demonstrated that the suprachiasmatic nucleus is rhythmic in vivo using a 2-deoxyglucose radioactive marker for functional brain imaging. As of 2014, he is editor of the Journal of Biological Rhythms.
Paul Hardin is a prominent scientist in the field of chronobiology and a pioneering researcher in the understanding of circadian clocks in flies and mammals. Hardin currently serves as a distinguished professor in the biology department at Texas A&M University. He is best known for his discovery of circadian oscillations in the mRNA of the clock gene Period (per), the importance of the E-Box in per activation, the interlocked feedback loops that control rhythms in activator gene transcription, and the circadian regulation of olfaction in Drosophila melanogaster. Born in a suburb of Chicago, Matteson, Illinois, Hardin currently resides in College Station, Texas, with his wife and three children.
Michael Harvey Hastings is a British neuroscientist who works at the Medical Research Council MRC Laboratory of Molecular Biology (LMB) in Cambridge, UK. Hastings is known for his contributions to the current understanding of biological clocks in mammals and marine invertebrates.
Johanna H. Meijer is a Dutch scientist who has contributed significantly to the field of chronobiology. Meijer has made notable contributions to the understanding of the neural and molecular mechanisms of circadian pacemakers. She is known for her extensive studies of photic and non-photic effects on the mammalian circadian clocks. Notably, Meijer is the 2016 recipient of the Aschoff and Honma Prize, one of the most prestigious international prizes in the circadian research field. In addition to still unraveling neuronal mechanisms of circadian clocks and their applications to health, Meijer's lab now studies the effects of modern lifestyles on our circadian rhythm and bodily functions.
References
- ↑ "The Body Might Have Built-In Dinner-Bell, Studies Hint". Miami Herald, Oct. 6, 1992.
- ↑ Cassone, Vincent (2005). "The Clock that Tells the Time". Nature Neuroscience. Nature. 8 (1): 1165. doi: 10.1038/nn0105-3 .
- ↑ Foster, Russell G.; Kreitzman, Leon (2005). Rhythms of Life: The Biological Clocks that Control the Daily Lives of Every Living Thing. Yale University Press. p. 88. ISBN 978-0-300-10969-6.
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