A03 Bio Rhythms: Endogenous Pacemakers/Exogenous Zeitgebers

• Beyond the master clock


  Research has revealed there are numerous circadian rhythms in many organs and cells of the body. These are called peripheral oscillators, and are found in the adrenal gland, oesophagus, lungs, liver, pancreas, spleen, thymus and skin.Although these peripheral clocks are highly influenced by the actions of the SCN,they can act independently.
• Damiola et al study (Beyond the master clock)


  Demonstrated how changing feeding patterns in mice can alter the Circadian rhythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SCN unaffected. This suggests that there may be many other complex influences on the sleep/wake cycle, aside from the master clock
• Ethics in animal studies

  Problems with generalising findings but also ethics like DeCoursey et al study where the animals were exposed to considerable harm and risk when returned to their natural habitat.
• Influence of exogenous zeitgebers may be overstated

  Miles et al recounted a study of a young blind man with a sleep/wake cycle of 24.9 hours and despite to social cues, his cycle could not adjust and therefore, sedatives had to be used. People who live in arctic regions show nomral sleep patterns despite prolonged exposure to light. Shows there are occasions zeitgebers may have little bearing on our internal rhythm.
• Methodological issues in studies

  Criticism of Campbell and Murphys tudy on the manner in which the study was conducted and suggsted there may had been limited light exposure for the ppts eyes. This is a major confounding varibale. Isolating one exogenous zeitgeber (light) in this way does not give insight on other zeitgerbers that influence the sleep/wake cycle.
• Interactionist system


  Only in excpetional circumstances are endogenous pacemakers free-running and unaffected by the influence of exogenous zeitgebers. Total isolationist studies like Siffre are reare and thus, could be judged as lacking valdity. In real life, pacemakers and zeitgebers interact and it makes little sense to separate the two for research as it is impractical.