Biological Rhythms

• what are endogenous pacemakers?

  • internal body clocks that keep biological processes to time
• what are exogenous zeitgebers?

  • external cues that entrain endogenous pacemakers, meaning altering body clocks to match environment
• what is a circadian rhythm?

  • biological rhythm that lasts 24 hours
  • e.gs the sleep-wake cycle, the release of hormones
• What is the Suprachiasmatic Nucleus?

  • the endogenous pacemaker for sleep-wake cycle
  • located at the optic chiasm (where optic nerves cross)
  • when light is detected by SCN, it sends the light to the pineal gland, stopping the production of melatonin which induces sleep
• examples of exogenous pacemakers for sleep-wake cycle?

  • LIGHT
  • SOCIAL CUES E.G WHEN WE EAT MEALS
  • ENVIRONMENTAL CUES E.G CLOCKS
• Siffre's Cave Study (1975) - Circadian Rhythms

  • sleep wake cycle EP thought to be free running, maintaining a predictable cycle without constant entertainment from EZs
  • Siffre spent 6 months in a cave with no light or other EZs
  • His EP maintained a regular cycle of around 25 hours
  • this suggests EP for sleep-wake is free-running but needs entertainment from EZs to maintain to the 24 hour day-night cycle
• Folkard et al (1995)

  • got participants to live in a cave for 4 weeks and go to bed at 11:45pm and wake up at 7:45pm
  • he then sped up the clock so the day was only 22 hours
  • participants struggled to adjust, suggesting endogenous pacemakers are the most influential on the sleep-wake cycle
• Limitations of Circadian Rhythm Research - Individual Differences

  • circadian rhythms too hard to generalise
  • it seems that sleep-wake cycles may vary depending on the person
  • this means that it is difficult to use research data to discuss anything more then averages, which may be meaningless
• Strength of circadian rhythm - shift work

  • due to sleep pattern disruption leading to anxiety and decreased alertion - an understanding will lead to solutions to the negative effects of jet lag and shift work
  • this means understanding circadian rhythms may have real-world economic implications in terms of how to best manage worker productivity.