Biological Rhythms - Circadian Rhythms

    Cards (5)

    • Biological Rhythms
      • Biological Rhythms are dictated by two things; the internal body clock (endogenous pacemakers) and external changes in the environment (exogenous zeitgebers)
      • Some of these rhythms occur multiple times a day (ultradian); some take longer than a day to complete (infradian)
      • Circadian rhythms are those that last around 24 hours, for example: sleep wake cycle and core body temperature
    • The Sleep-Wake Cycle
      • Light, which is an exogenous zeitgeber, is an important factor in the sleep-wake cycle; we feel tired at night and alert during daylight
      • However, there is also a endogenous pacemaker that influences the cycle - the suprachiasmatic nucleus, just above the optic chiasm, which provides information from the eye about light
      • Exogenous Zeitgebers can also reset the SCN
    • Siffre's Cave Study
      • He has spent several periods underground to see the effects on his own biological rhythms, deprived of sound or light
      • In each case, his 'free-running' biological rhythm settled down to 25 hours, but he still did fall asleep and wake up on a regular schedule
    • Aschoff & Weaver's Studies
      • Had a group of participants spend 4 weeks in a WW2 bunker, deprived of natural light
      • All but one of the participants displayed a circadian rhythm between 24 to 25 hours
      • Together with Siffre, this suggests that the natural sleep wake cycle is longer than 24 hours, but it is affected by exogenous zeitgebers (number of daylight hours, typical mealtimes)
    • Simon Folkard's study
      • Studied a group of 12 people who agreed to live in a dark cave for 3 weeks; they retired to bed at 11.45pm and woke up at 7.45
      • Over the course of the study, researchers sped up the clocks (unknown to participants)
      • The normal 24 hour days only then lasted 22 hours
      • This then suggests that a strong 'free-running' circadian rhythm cannot be easily affected by exogenous zeitgebers