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Discuss the role of endogenous pacemakers and exogenous zeitgebers in the sleep/wake cycle, and at least one other biological rhythm

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´╗┐Discuss the role of endogenous pacemakers and exogenous zeitgebers in the sleep/wake cycle, and at least one other biological rhythm The sleep/wake cycle is a circadian rhythm, which means that it rotates a full cycle every 24 hours, and is controlled and regulated through endogenous pacemakers and exogenous zeitgebers. Endogenous pacemakers are inbuilt biological clocks that regulate our behaviour, such as the sleep/wake cycle, stages of sleep and the menstrual cycle. Exogenous zeitgebers, such as lights or clocks, keep us regulated with the outside world. It is believed that humans have many endogenous pacemakers, some of which have yet to be identified. In this essay I will be discussing research that helps us to understand the role and importance of endogenous pacemakers and exogenous zeitgebers. The biological clock that regulates the sleep/wake cycle in mammals is called the Suprachiasmatic Nucleus (SCN), found in the primitive area of the brain, and the exogenous zeitgeber that acts upon it is light. When the optic nerves at the back of the eyes can sense light, the Suprachiasmatic Nucleus doesn?t function. But when the optic nerves sense a lack of light it sends a signal through the optic chiasm to the Suprachiasmatic Nucleus. ...read more.


studied American submariners who were working 6 hour shifts, with 12 hours off, this created an 18 hour day. Even though they could control their lighting conditions, they still kept a 24 hour sleep/wake cycle, this is because they had contact with family and friends who had a normal 24 hour sleep/wake cycle. This shows that sometimes light isn?t the most prominent and important zeitgeber. There are also some studies, in which researchers attempt to artificially alter the length of the participant?s day. One of these studies was Kleitman (1963), who put two participants in an environment where they were exposed to a 28 hour day with 9 hours of sleep and 19 hours of activity. He did this by using artificial light to keep them awake. Only one of the participants managed to adapt quite well, but the other was unable to do so and kept trying to revert to a 24 hour day. The other study was conducted by Folkard et al (1985), he did a similar study with 12 participants who attempted to adapt to a 22 hour day. ...read more.


They used a sample of female university students, none of which were taking birth control pills. The control group of women wore an alcohol pad under their armpits, which soaked up the pheromones. These fumes were then inhaled by the experimental group and their menstrual cycle was monitored. When the experimental group inhaled secretions from women who were about to ovulate, their menstrual cycles became shorter. When they inhaled secretions from women who had just ovulated, their menstrual cycles became longer. The experimental groups? menstrual cycles were affected by the secretions from the control group. This explains why when a group of women live in close proximity their menstrual cycles tend to synchronise. Although McClintock?s and Stern?s findings show that the menstrual cycle is influenced by zeitgebers, and explain to an extent how women?s menstrual cycles can come to synchronise, it is still not clear why this should happen. It may well be that there was once an evolutionary advantage to having all the women in a community menstruate at approximately the same time, but there is no strong evidence as yet. How it happens. Human response to pheromones is not yet well understood, and researchers have not yet discovered the precise substance involved of the mechanism by which it affects the menstrual cycle. ...read more.

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