Discuss the influence of endogenous pacemaker and exogenous zeitgebers on one or more biological rhythms (24 Marks)
This essay will outline and evaluate the role that endogenous pacemakers (ep’s) or internal clocks have on our biological cycles. It will also consider exogenous zeitgebers (ez’s) or external timekeepers. The two cycles to be considered are circadian and ultradian.
Psychologists believe that the circadian rhythm (sleep/wake) is controlled by an ep located in the SCN. This clock controls when we sleep and feel drowsy and when we awake and feel alert. It makes sure that our biological processes such as blood sugar and heart rate peak in the day when we need energy and fip at night to save energy. it also makes sure they are synchronised. As this cycle is approximately 25 hours, we need light to act as an ez to help us reset out clock each day to match the earths 24 hours pattern.
Evidence to support this comes from Aschoff. He did an experiment where participants (pps) were put in an underground world war 2 bunker for three to four weeks at a time with no ez’s such as our clocks or light. They settled into a regular 25 hour cycle of sleep wake. This is clear evidence that in the absence of ez’s we have a regular sleep/wake pattern that we must be controlled by a clock. As the pps were out of sync with the 24 hour day, it is evidence that we must use ez’s such as light to re-set our clock.
More evidence comes from Siffre. He lived in a cave underground in Texas for 6 months and was monitored by Nasa. He settled into a 24.5 hour regular cycle but was out of sync with the 24 hour pattern of day and night. Siffre must have been controlled by an ep that was out of sync. He had no light to re-set his clock and so when he came out far more time had passed than he thought. The only explanation for this is that we have ez’s to re-set our clock.
One last piece of evidence to support comes from...
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