Circadian Rhythm

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Circadian Rhythms

  • Biological cycles lasting around 24 hrs.
  • Exogenous Zeitgeber: 'Time giver' external stimuli.
  • Endogenous Pacemakers: Biological 'clocks' in the brain controlling biological rhythms.
  • Free-running is when our biological clock is allowed to run unaffected by external cues.
  • Cortisol is a hormone produced when we are stressed but it also relates to keeping us alert

Sleep wake cycle

  • Michel Siffre offers support for a free running rhythm. He lived in a cave with no access exogenous zeitgebers and as a result his CR settled down to just 24 hrs but it would vary to as much as 48 hours. This shows that light is necessary to keep the CR in balance with 24 hr clock.
  • Aschoff and Weber '62 p's put in isolation, CR settled between 24-27 hrs. Demonstrates that light seems necessary to coordinate the biological clock with the external environment.

Hormones

  • Cortisol highest around midnight and peaks at 6am. This explains why if we're woken up around…

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