endogenous pacemakers and exogenous zeitgebers

Question 1

evaluate endogenous pacemakers

Answer 1

Beyond the master clock (limitation)
- research has revealed that there are numerous circadian rhythms in many organs and cells in the body. The peripheral oscillators are found in the organs including the lungs, pancreas and skin. They are influenced by the actions of the SCN but also act independently. Francesca Damiola et al. (2000) demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SCN unaffected. This suggests other complex influences in the sleep/wake cycle

Interactions system (limitation)
- they cannot be studied in isolation
- total isolation studies such as Siffre’s cave study are extremely rare. In everyday life, pacemakers and zeitgebers interact and it may make little sense to separate the two for the purpose of research. This suggests the more researchers attempt to isolate the influence of internal pacemakers, the lower the validity of the research.

Question 2

evaluate the role of exogenous zeitgebers on the sleep/wake cycle

Answer 2

Environmental observations (limitation)
- they don’t have the same affect in all environments
- the experience of people who live in places where they have very little darkness in summer and very little light in winter tell a different story from the usual narrative. E.g those who live in the arctic circle have similar sleep patterns all year round despite spending six months in almost total darkness.
- this suggests the sleep/wake cycle is primarily controlled by endogenous pacemakers that can overrride environmental changes in light

Case study evidence (limitation)
- challenges its role
- Miles et al. (1977) recount the study of a young man, blind from birth, who had an abnormal circadian rhythm of 24.9 hours. Despite exposure to social cues, such as regular mealtimes, his sleep/wake cycle could not be adjusted
- this suggests that social cues alone are not affective in resetting the biological rhythm