Circadian rhythms

• What governs all biological rhythms?

  Endogenous pacemakers and exogenous zeitgebers
• What is a biological rhythm that lasts 24 hours?

  Circadian rhythm
• How is the circadian rhythm reset?

  By levels of light
• What does the sleep-wake cycle dictate?

  When humans and animals should sleep and wake
• What is the primary input for the sleep-wake cycle?

  Light
• How is light detected in the sleep-wake cycle?

  By the eyes sending messages to the SCN
• What role does the SCN play in the circadian system?

  Coordinates the activity of the circadian system
• What other factor influences sleep and wakefulness besides circadian rhythm?

  Homeostasis
• What does homeostasis indicate when an individual is awake for a long time?

  There is a need for sleep
• When does the homeostatic drive for sleep reach its maximum?

  In the late evening
• When is human body temperature lowest?

  In the early hours of the morning
• When does sleep typically occur in relation to body temperature?

  When core temperature starts to drop
• What happens to body temperature towards the end of a sleep cycle?

  It starts to rise, promoting alertness
• What did Siffre's study reveal about external cues and circadian rhythms?

  Absence of cues altered his circadian rhythms
• What did Siffre believe about the date after his underground stay?

  It was one month earlier than it was
• What does Siffre's experience suggest about the 24-hour sleep-wake cycle?

  It can be increased by lack of cues
• What did Aschoff and Weaver study in their experiment?

  Circadian rhythms in a WW11 bunker
• What was the circadian rhythm range observed in Aschoff and Weaver's participants?

  Between 24 and 25 hours
• What does the Aschoff and Weaver study suggest about the natural sleep-wake cycle?

  It may be slightly longer than 24 hours
• What did Folkard et al study in their experiment?

  Participants living in a dark cave
• What was the clock adjustment in Folkard et al's study?

  Clock was sped up to 22 hours
• How many participants adjusted to the new regime in Folkard et al's study?

  Only one participant
• What does Folkard et al's study suggest about circadian rhythms?

  They are strong and hard to override
• What are the practical applications of understanding circadian rhythms in shift work?

  • Reduced concentration around 6 AM (Bovin et al)
  • Increased risk of mistakes and accidents
  • Relationship between shift work and health issues (Knutsson)
  • Economic implications for managing worker productivity
• How do circadian rhythms affect drug treatments?

  • Coordinate basic processes (heart rate, digestion)
  • Influence drug absorption and distribution
  • Peak effectiveness at certain times (Baraldo)
  • Guidelines for drug dosing timing
• What are the weaknesses in studies of circadian rhythms?

  • Poor control due to artificial light access
  • Czeisler et al's findings on light's effect
  • Artificial light acts as a confounding variable
  • Decreases internal validity of studies
• What individual differences exist in circadian rhythms?

  • 'Morning people' prefer early sleep/wake
  • 'Evening people' prefer later sleep/wake
  • Innate differences suggest focus on these variations