Discuss the role of endogenous pacemakers in the control of one or more biological rhythms.
24 marks
Endogenous pacemakers are internal ‘biological clocks’ that manage our rhythms. In humans, the main biological clock is the suprachiasmatic nucleus (SCN), which is located in the hypothalamus. This controls circadian rhythms. The SCN is located above the optic chiasm. When light hits the retina it transfers through the optic nerve to the SCN, which stimulates the release of hormones such as cortisol and melatonin in the pineal gland. Thus, maintain our sleep-wake cycle.
It has been suggested by evolutionary psychologists that endogenous pacemakers (EP) have an adaptive value in controlling biological rhythms such as the sleep-wake cycle, suggesting it aids survival. This is supported by studies such as DeCoursey (1998) who found that removing the SCN in 30 chipmunks and returning them to their natural habitat, proved costly for their survival. They found that after 80 days significantly more chipmunks had died compared to a control group with normal functioning SCNs. Therefore, this suggests that EP, most importantly the SCN, indeed aids survival, as the absence of this important EP proved detrimental for the survival of the chipmunks.
Furthermore, the famous study of free-running biological rhythms in 1972 involving Michel Siffre supports the presence of EP in our sleep-wake cycle. This was demonstrated as Siffre spent 6 months in a cave in Texas, separated from the influence of exogenous zeitgebers (EZ) such as light. He found that at first his sleep pattern was erratic, but settled then down to a regular pattern of 25-30 hours. Despite the absence of exogenous zeitgebers, circadian rhythms were maintained, supporting the existence of an internal ‘body clock’.
However, there is a view that EP are limited in their control of circadian rhythms (such as the sleep wake cycle) and EZ are needed to regulate rhythms to keep them in line with the ever changing...