Circadian rhythms

• Circadian rhythms definitions


  Rhythms that last around 24 hours long
• Endogenous pacemakers definition


  Your internal body clock
• Exogenous zeitgebers


  External changes in the environment
• Siffre's cave study (1962)

  • Spent 63 days underground
  • to see whether sleep/wake cycle is free running or trained
  • deprived of natural light + sound, had access to food + drink
  • days blended together, difficult to distinguish between psychological clock or real clock
  • free running biological rhythm settled down to one that was beyond usual 24 hours, continued to fall asleep + wake up on regular schedule
• Sleep/wake cycle example

  1. Light increases/decreases (EZ)
  2. Eyes detect change, passes message to SCN (EP)
  3. Suprachiasmatic nucleus (SCN) in the hypothalamus detects changes in light levels (EP)
  4. Causes the pineal gland to release/stop releasing melatonin (EP). light increase = stops melatonin = increases brain activity. vice verca
• A03 of EPS & EZS of circadian rhythms - Supporting research


  After 63 days in a cave, Siffre found both EPs and EZs play a key role in sleep/wake cycle. This is supported further by research from Aschoff & Wever, who sent a small group to spend 4 weeks in a WW2 bunker (sleep/wake cycle stayed between 24/25 hours).

  CA: exposure to artificial lights like torches/phones was not controlled (they assumed only natural light affected it) - may lack validity
• A03 of EPS and EZS of circadian rhythms - Pharmacokinetics

  Understanding circadian rhythms and their impact on health can help determine the best time to give drug treatments. E.g. risk of heart attack = greatest in early morning, so drugs can be taken at night and released when they're most effective at dusk