Circadian Rhythms

• What are the three biological rhythms in our body?

  Circadian, infradian, and ultradian rhythms
• What is a circadian rhythm?

  A cycle that occurs in a 24-hour cycle
• What is an infradian rhythm?

  A cycle that takes longer than 24 hours
• What is an ultradian rhythm?

  A cycle that takes less than 24 hours
• What is an endogenous pacemaker?

  An internal body clock regulating rhythms
• What are exogenous zeitgebers?

  External factors that change biological rhythms
• What does it mean for a circadian rhythm to be free-running?

  It may deviate without external cues
• What happens to circadian rhythms in prolonged darkness?

  They may lead to longer sleep/wake cycles
• Who conducted a case study in a cave?

  Siffre
• What was Siffre's experience in the cave?

  He lived without indications of daylight
• What was the result of Siffre's study after 6 months?

  He had a 25-hour sleep/wake cycle
• What does Siffre's study suggest about circadian rhythms?

  They can continue without external cues
• What are the implications of research on night shift work?

  • Increased likelihood of self-harm in morning
  • Suggests changes in occupational health guidelines
• What did the WW2 bunker study reveal about body clocks?

  • Importance of natural light for body clocks
  • One participant extended sleep/wake cycle to 29 hours
• What are the limitations of case studies in biological rhythms research?

  • Specific to individual behaviors
  • Reduces replicability and validity of results