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However, when mammals are placed in an environment void of nearly all outside influences, also known as zeitgebers, these rhythms continue to run at specified intervals. Thus, the endogenous rhythm must be governed by an internal “master clock.” This master clock has been discovered to be the suprachiasmatic nuclei which are located in the anterior portion of the hypothalamus. Circadian rhythms are endogenous rhythms that mammals and plants exhibit. The term “circadian” was established in the 1950’s and is derived from the Latin prefix circa- which means “approximately,” and dies- which means “day.”
It receives information about incoming light from the optic nerves, which relay information from the eyes to the brain. When there is less light—like at night—the SCN tells the brain to make more melatonin so you get drowsy. Researchers are studying how shift work as well as exposure to light from mobile devices during the night may alter circadian rhythms and sleep-wake cycles. People get jet lag when travel disrupts their circadian rhythms. When you pass through different time zones, your biological clocks will be different from the local time. For example, if you fly east from California to New York, you “lose” 3 hours. When you wake up at 7:00 a.m. on the east coast, your biological clocks are still running on west coast time, so you feel the way you might feel at 4:00 a.m. Your biological clocks will reset, but this often takes a few days.
Recent evidence indicating a high degree of stability in neurobehavioral responses to sleep loss suggests that these trait-like individual differences are phenotypic and likely involve genetic components, including circadian genes. Recent experiments have revealed both sleep homeostatic and circadian effects on brain metabolism and neural activation. Investigation of the neural and genetic mechanisms underlying the dynamically complex interaction between sleep homeostasis and circadian systems is beginning (Katzenberg D, Young T, Finn L, 1998). A key goal of this work is to identify biomarkers that accurately predict human performance in situations in which the circadian and sleep homeostatic systems are perturbed.
Once further research involving human as test subjects, and more factors that may effect metabolic function are studied, results may be able to aid in treating detrimental metabolic disorders in today’s society. For now, the reviewed research gives us further knowledge into the complexity of metabolism and its integration with circadian rhythmicity.
Barclay NL, Gregory AM. Quantitative genetic research on sleep: a review of normal sleep, sleep disturbances and associated emotional, behavioural, and health-related difficulties. Sleep Med Rev. 2013
Takahashi JS, Hong HK, Ko CH, McDearmon EL. The genetics of mammalian circadian order and disorder: implications for physiology and disease. Nat Rev Genet. 2008
Katzenberg D, Young T, Finn L, Lin L, King DP, Takahashi JS. A CLOCK polymorphism associated with human diurnal preference. Sleep. 1998