Discuss the Role of Endogenous Pacemakers

Discuss the role of endogenous pacemakers in the hold of circadian turns AO1 8 marks, AO2 16 marks An endogenous pacemaker is an internal biological clock that carrys the way in which human beingy of our biological measures be take. M both of these rhythms depart on a 24 hour basis, such as the remainder/wake cycle, bodily temperatures and some of our hormones. The main endogenous pacemaker in mammals is the suprachiasmatic nucleus (SCN), which is located in the hypothalamus. It receives information ab disclose thinlys from the eye finished the optic nerve.This happens even when our eyes are shut, due to them being so thin, meaning that if our endogenous clocks are slow (e. g. because the sun rises in the first place than the twenty-four hour period before) morning light automatically shifts the clock ahead, putting the rhythm back in sync with the day. At night, when there is no light, the SCN past sends a message to the pineal gland, causing it to increase the productio n of melatonin, which induces pile by preventing the brains mechanism to promote wakefulness.An example of the way endogenous pacemakers control our circadian rhythms is a case study on Michael Siffre. Siffre willingly washed-out a long period of time under ground, to find out what happens to the eternal rest/wake cycle when the biological rhythm is allowed to run freely without outer cues. His findings showed that the free running cycle settled down to a regular rhythm which is little over 24 hours. This study shows that the circadian rhythm persists without the cues of natural light, which demonstrates the existence of an endogenous clock.However the study alike shows that external cues are also important to the sleep/wake cycle, because the clock was non perfectly accurate, meaning that without the cues of natural light, it would receive out of sync with day and night. This study was supported by Aschoff and Wever (1985) who placed participants in an underground lying in wait without any external cues , and found that many participants uncovered circadian rhythms of between 24 and 25 hours. However some of the circadian rhythms of those in the bunker were as long as 29 hours, showing that individual differences can rig the results meaning this study and the case study of MichaelSiffre cannot be generalised to the wider population. Miles et als (1977) study of a man that had been blind since birth showed that the man had a circadian cycle of 24. 9 hours. The blind man was subject to different exogenous zeitgebers such as clocks and social cues, that they found that none of these factors reduced his biological clock to 24 hours, and he had to take stimulants in the morning and sedatives at certain times at night to reduce his biological rhythm in time with the tolerate of the world.This research supports the idea that the sleep/wake cycle isa circadian rhythm controlled by an endogenous pacemaker as it did not adjust when influenced with any nat ural exogenous zeitgebers, and was only pitched when certain drugs were used to mixture it. However this study can be criticized as it is only a case study of one man, meaning it lacks population validity and cannot be generalised to the wider population. Morgan et al (1995) also provided evidence for the effect of endogenous pacemakers of the circadian rhythms by breeding mutant hamsters that had circadian rhythms of 20 hours instead of 24.He and then cut the SCNs out of the mutant hamsters and transplanted them into normal hamsters. The normal hamsters the began to dis defend the 20 hour circadian rhythm of the mutant hamster. This proves that endogenous pacemakers play a double role in circadian rhythms, as it showed that the sleep cycle in the hamsters depended on biological factors from with in the brain. However this research may raise some ethical issues as it can be seen to breach the terms of animal cruelty, as it may cause the hamsters to become psychologically unhealt hy.Also the research can be criticized as it only shows the effect of the SCN on hamsters sleeping cycles and cannot be generalised to humans as hamsters have much smaller brains and are also nocturnal animals meaning that light does not effect their circadian rhythms, the same way it does ours. In conclusion, I think that endogenous pacemakers do play a very large role in helping to maintain our circadian rhythms, however this is also with the help of various exogenous zeitgebers which help keep the rhythms precise.