Circadian Rhythms

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  • Circadian Rhythms
    • Circadian rhythms are biological rhythms that last about 24 hours. sleep wake cycle.
    • It is thought; controlled biologically by endogenous pacemakers in supracharismatic nucleaus in the brain
    • Michel Siffre study to test whether CR is free running in humans.
      • 61 days in a cave alone. thinking it was almost a month before. 2nd time- settled down to about 24 hours but could change dramatically. 3rd- he was 60 and found clock was slower.
    • Sleep wake cycle. exogenous zeitgebers are things such as daylight and clocks. endogenous pacemaker is free running and has a cycle of about 24 hours. howver it is helped by external cues.
    • Core body temperature. lowest- 4:30am and highest 6pm. slight trough just after lunch when people haven't eaten.
    • Hormones. Cortisol is at its lowest around midnight and peaks around 6am. cortisol is produced when we are stressed but also keeps us alert. also melatoning and growth hormone.
    • Aschoff and weaver ('76). P's in a WWII bunker without exogenous zeitgebers. found that most had 24-25 hour circadian rhythms. some up to 29 hours.
    • Cycle operates in absence of exogenous zeitgebers. natural free running cycle is about 24 hours. BUT it could be because they are in a group.
      • Aschoff and weaver ('76). P's in a WWII bunker without exogenous zeitgebers. found that most had 24-25 hour circadian rhythms. some up to 29 hours.
    • Folkard et al. could external cues override the internal clock? 12 people in a cave for 3 weeks. went to bed at 11:45 and woke at 7:45. started to speed up the clock to a 22 hour cycle. only one adapted.
      • Can be guided to a limited extent.
    • Michel Siffre- case study so cant generalise. caves aren't normal surroundings (cold). was an experiment so there were variables. he did it on himself so might be biased. he was used to caves- cave explorer.
    • IDA- chronotheraputics. medication- Asprin for heart attacks. most happen in the morning so taking them at 11pm will give chance to thin the blood.
    • Biological and determinist approach. biologically controlled.
      • Miles et al. blind boy who was exposed to clocks but didnt see daylight. the external cues didnt make much difference to his circadian rhythm.
      • Can be misleading as there is some flexibility. sometimes we go to bed later and wake up earlier.

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