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Describe and critically asses the evidence that suggests the circadian rhythm is controlled by endogenous factors.

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Introduction

Describe and critically asses the evidence that suggests the circadian rhythm is controlled by endogenous factors. The Circadian rhythm is a 24 hour cycle which occurs in humans in hormone levels, body temperature, heart, respiration and metabolic rate and sleep pattern. The circadian sleep-waking pattern is of most interest to psychologists because of the dramatic changes in behaviour it produces. The circadian sleep-wake pattern is said to be governed by many different factors, both endogenous and exogenous, which both have input into the circadian cycle in different ways. There are many endogenous pacemakers which can be said to have great effect on the 24 hour circadian sleep-wake pattern. The first is the biological clock, which is the interaction between proteins. Darlington et al., 1998, described one clock. They thought two proteins, Clock and Cycle linked together in the morning, due to this binding two other proteins increase their production during the day, they are Per and Tim. ...read more.

Middle

Light is an exogenous factor and recently has been seen as one of the most important of the exogenous factors to affect the circadian rhythm. Wever et al., 1983, proved that exposure to bright light restrains melatonin production meaning that daylight will re-set the biological clock as seen by SCN but dim artificial light is less effective. Light is said not just to affect the SCN, but also certain proteins in the body have detected changes in light as proved by Hall, 2000. The importance of light as an exogenous zeitgeber can be seen in the experiment conducted by Miles et al., 1977. They proved that the lack of information given by light ruins their sleeping patterns. A final endogenous factor is the pineal gland and melatonin which as well as the SCN is another pacemaker in the brain. ...read more.

Conclusion

For example, deciduous trees have leaves which change colour and drop off because of the changes in temperature. Temperature is also a factor in the beginning of hibernation, however there is little evidence that temperature affects human biological rhythms. Both endogenous and exogenous factors contribute to and control the circadian rhythm. However, endogenous pacemakers due to their fundamental position within the body appear to dictate the circadian rhythm a lot more than the exogenous factors. Often the two coincide and combine, for example, in SCN light is a strong factor and without it an organism would not adapt truly to how the world is. It seems clear that endogenous factors are slightly more important than exogenous zeitgebers, particularly for example temperature which is said to not play a part in human biological rhythms at all in the circadian rhythm. Endogenous pacemakers seem to govern the circadian rhythm more but exogenous zeitgeber appear necessary also for an organism's cycle to adapt to the outside world. ...read more.

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