Circadian Rhythms

• What governs the sleep/wake cycle?

  Endogenous pacemakers
• Name one endogenous pacemaker involved in the sleep/wake cycle.

  SCN
• How is the sleep/wake cycle 'entrained'?

  By exogenous zeitgebers
• What happens to melatonin production during the daytime?

  It is suppressed by the pineal gland
• What induces the state of 'sleepiness' at night?

  Production of melatonin by the pineal gland
• What role do social cues play in the sleep/wake cycle?

  They help entrain the cycle
• What did Decoursey et al. (2000) study about the SCN?

  • Destroyed SCN connections in chipmunks
  • Observed them for 80 days in natural habitat
  • Result: Sleep/wake cycle disappeared
  • Most chipmunks were killed by predators
• What did Campbell & Murphy (1998) demonstrate about light's role in the sleep/wake cycle?

  • Woke participants at various night points
  • Shone artificial light on participants' knees
  • Result: Deviation of three hours in sleep/wake cycle
  • Conclusion: Light can entrain the cycle
• • With no exposure to natural light and sound, but still with access to adequate food and drink, Siffre spent 2 months in his underground cave in September 1962, believing it to be mid-August...
  • 10 years later he repeated this feat in a Texan cave but for 6 months
• What was the duration of the 'free-running' biological rhythm observed?

  Around 25 hours
• What does the 'free-running' biological rhythm demonstrate about the sleep/wake cycle?

  It is governed by endogenous pacemakers
• How does the sleep/wake cycle remain regular despite the 'free-running' rhythm?

  It is entrained by exogenous zeitgebers
• What role does light play in the sleep/wake cycle according to the study material?

  Light acts as an exogenous zeitgeber
• What are the two main factors that interact to maintain the sleep/wake cycle?

  • Endogenous pacemakers
  • Exogenous zeitgebers