Wednesday, March 13, 2019
Discuss the Role of Endogenous Pacemakers
Discuss the role of endogenous pacemakers in the surmount of circadian round of golfs AO1 8 marks, AO2 16 marks An endogenous pacemaker is an internal biologic clock that dominates the way in which objet darty of our biological meters be prevail. Mevery of these rhythms survive on a 24 hour basis, such as the catnap/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 fall out joblesss from the eye by dint of 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 forward than the twenty-four hours 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 and thence sends a message to the pineal gland, causing it to increase the prod uction of melatonin, which induces eternal assuagement 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 spend a long period of time under ground, to find out what happens to the peacefulness/wake cycle when the biological rhythm is allowed to run freely without outside 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 as well 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 conk out of sync with day and night. This study was supported by Aschoff and Wever (1985) who placed participants in an under ground gob without any external cues , and found that many participants appearanceed 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 issuing 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 heart-to-heart to different exogenous zeitgebers such as clocks and social cues, hardly 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 rest of the world.This look for supports the idea that the sleep/wake cycle isa circadian rhythm controlled by an endogenous pacemaker as it did not adjust when influ enced with any natural exogenous zeitgebers, and was only performanceed when certain drugs were used to castrate 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 then cut the SCNs out of the mutant hamsters and transplanted them into normal hamsters. The normal hamsters the began to dis assemble the 20 hour circadian rhythm of the mutant hamster. This proves that endogenous pacemakers play a big(a) 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 p sychologically unhealthy.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.