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Biological Rhythms

All plants and animals have endogeous cycles that, in response to an outside rhythm (zeitgeber), will cue various actions.For example, bears know they must hibernate, poinsettias know they must flower and humans know they need sleep.In correspondence with a particular season, length of day, and light intensity respectively, these events will occur.In the example with the poinsettia, the vegetative/flower cycle is synchronized with a day length cycle that has longer hours of darkness, resulting in a chemical reaction that releases florigen and signals to the poinsettia to flower.Similarly, a chemical reaction takes place in humans with their sleep/wake cycle.This will be discussed in the essay along with disorders associated with this cycle.
Humans possess many biological clocks.Depending on the cycle it could be an infradian (longer than a day), ultradian (shorter than a day), circadian (about a day), or circannual (about a year) rhythm.In the case of the human's internal sleep/wake cycle, it's a circadian rhythm.The human sleep/wake cycle is a bit longer than 24 hours (closer to 25 hours), therefore it needs an entraining agent or zeitgeber.This is an external environmental rhythm which will keep it in sync with the 24 hour day.The most dominant cycle is the light/dark cycle.However, it's necessary to transmit the external information to the internal cycle so that synchronization is achieved.
As infants, our sleep/wake cycle was initially random compared to that of our parents or guardian.Eventually, over the course of 6 weeks, we began to adapt the circadian cycle and after approximately 4 months, we were entrained to the 24-hour cycle.This is due to the external cues of our parents/guardian.
The human clock is found in the suprachiasmatic nucleus (SCN), which is a group of distinct cells in the hypothalamus, which is located in the brain.Light from the outsid

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