Biological Rhythms: Circadian rhythms


Biological ryhthms: Circadian rhythms 

Circadian rhythms

  • Biological rhythms
    • Biological rhythms exert an important influence on the way in which body systems behave
    • All biological rhythms are governed by two things:
      • The body's internal biological 'clocks', endogenous pacemakers
      • External changes in the environment, exogenous zeitgebers
    • Circadian rhythms last for around 24 hours
  • The sleep/wake cycle
    • The fact we feel drowsy at night-time and alert during the day demonstrates the effect of daylight- an important exogenous zeitgeber on our sleep/wake cycle
  • Siffre's cave study
    • Siffre spent several extended periods underground to study the effects on his own biological rhythms
    • Deprived of exposure to natural light and sound but with access to adequate food and drink, Siffre resurfaced after two months in the caves, believing he had only been there for one month
    • His biological rhythm settled down to one that was just beyond the usual 24 hours though he did continue to fall asleep and wake up on a regular schedule
  • Other research
    • Aschoof and Wever recorded similar results when they convinced a group of ppts to spend 4 weeks in a ww2 bunker deprived of natural light
    • All but one ppt displayed a circadian rhythm of 24 and 25 hours
    • Both Siffre and the bunker study suggest that the 'natural' sleep/wake cycle may be slightly longer…


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