Discuss the role of endogenous pacemakers in at least one biological rhythm

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Discuss the role of endogenous pacemakers in at least one biological rhythm

Endogenous pacemakers and exogenous zeitgebers can manipulate the various bodily rhythms, and have particular effects on the sleep-wake cycle in the circadian rhythm. Endogenous pacemakers are separate and distinct internal rhythms that affect the bodily rhythms; similarly, exogenous zeitgebers are outside influences, and sometimes outside rhythms that also affect how the bodily rhythms work. There are copious amounts of research into these variables, however, some are contradictory towards each other and pose many questions about not only the nature of these variables but also of the bodily rhythms themselves.

Endogenous pacemakers are rhythms generated internally by the organism in the absence of exogenous zeitgebers. This definition does however, cause problems in measuring EPs alone, as even when you methodology remove the affects of EZs, you can never fully be aware of all external events that may affect the rhythm. The main EP is the suprachiasmatic nucleus, which generates circadian rhythms from sensitivity to light. This shows that while both EPs and EZs are important, it seems that the SCN is the overriding factor even though it is affected by the EZ of light. Evidence supporting this claim was found in the removal of the SCN in hamsters, where it was found their circadian rhythm disappeared and failed to return after the transplant. While this study is scientifically rigorous in terms of controlling variables, you cannot generalise from hamsters to humans as we are significantly biologically different. Furthermore, this raises the issue of animal testing and the ethical issues associated with such studies. The SCN is a group of cells in the hypothalamus above the optic chiasma, which reacts to light, influencing the circadian rhythm. The SCN regulates the pineal gland which secretes melatonin in the absence of light as observed by the SCN and thus inducing sleep.

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Exogenous zeitgebers are external stimuli which may be rhythmic and act like a prompt, affecting internal rhythms. For example, day length is the dominant EZ as proved by Miles’ case study, where light is the dominant cue and the blind man was unable to have a normal circadian rhythm, but proved that it can be overcome. Luce and Segal disputed the fact that light is the dominant cue. Studying the arctic circle where light is either constantly available or never, found that the participants had a sleep cycle for seven hours which was based on social cues and was ...

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