Discuss the role of endogenous pacemakers in the control of circadian rhythms [AO1 8 marks, AO2 16 marks]
An endogenous pacemaker is an internal biological clock that controls the way in which many of our biological rhythms behave. Many of these rhythms run on a 24 hour basis, such as the sleep/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 about lights from the eye through 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 earlier than the day 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 then sends a message to the pineal gland, causing it to increase the production of melatonin, which induces sleep 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 spent a long period of time under ground, to find out what happens to the sleep/wake cycle when the biological rhythm is allowed to run freely without external 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 also shows that external cues are also important to the sleep/wake cycle, because the clock was not perfectly accurate, meaning that without the cues of natural light, it would become out of sync with day and night. This study was supported by Aschoff and Wever (1985) who placed participants in an underground bunker without any external cues , and found that many participants displayed...
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