Circadian Rhythms

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    Created by
    evie rose

    Cards (14)

    • biological rhythms 

      distinct patterns of changes in body activity that conform to cyclical time periods
    • circadian rhythm 

      a type of biological rhythm that recurs approximately every 24 hours, which regulates a number of body processes
    • 3 main body processes circadian rhythms regulate
      • sleep-wake cycle
      • core body temperature
      • hormone production
    • sleep-wake cycle
      • dictates when we should be asleep/awake
      • affected by light
      • has 2 dips: 2-4am and 1-3pm
    • what happens to the core body temperature when we sleep 

      decreases
    • hormone production when we sleep 

      increases when we sleep. the pineal gland produces melatonin which peaks in darkness
    • 'free-running' sleep-wake cycle 

      it will maintain a cycle of about 24-25 hours even in the absence of external cues
    • research studies that show support for a 'free-running' circadian rhythm
      • Michel Siffre's cave study (1962)
      • Aschoff and Wever (1976)
    • Michel Siffre's Cave study (1962) PROCEDURE 

      Michel Siffre spent several extended periods underground to study the effects on his own circadian rhythms. he had no external cues to guide his rythms (no daylight, clocks, etc). the only thing influencing his behaviour was his 'free running' circadian rhythm
    • Michel Siffre's Cave study (1962) FINDINGS 

      he found that his 'free-running' biological rhythm settled down to one that was just beyond the usual 24 hours (around 25 hours)
    • Michel Siffre's Cave study (1962) CONCLUSION 

      this suggests that the natural sleep-wake cycle may be slightly longer than 24 hours, but shows that our circadian rhythm is 'free-running' in the absence of external cues
    • Aschoff and Wever (1976) PROCEDURE 

      a group of participants spent 4 weeks in a WWII bunker deprived of natural light
    • Aschoff and Wever (1976) FINDINGS 

      all but one of the participants displayed a circadian rhythm between 24 and 25 hours
    • Aschoff and Wever (1976) CONCLUSIONS 

      a person's natural sleep/wake cycle is around 25 hours, but it is entrained by external stimuli associated with our 24-hour day (such as number of daylight hours, meal times etc)