Circadian rhythm

• Circadian rhythm-

  • 24 hour cycle
  • Distinct patterns and changes in our bodies
  • Cycles are full circles
  • Controlled by endogenous pacemakers (internal) and exogenous zeitgebers (external)
• Circadian rhythm-

  Sleep/wake cycle-

  • Exogenous zeitgebers in this cycle is the daylight.
  • Daylight comes into our eyes and stimulated the optic nerve, which sends a message to the SCN then to the pineal gland, to stop the production of melatonin.
  • Night time has the same process, but the darkness stimulates the production of melatonin, so we can go to sleep
  • Endogenous pacemakers is the internal body clock (SCN)
• Circadian Rhythm-

  Siffre 1975-

  • Free running case study
  • 6 months in a cave, alone, with no natural light or indication of day or night, just a torch to navigate
  • Had a 25-30 hour sleep/wake cycle, on a regular cycle  
  • Thought he was only there for a month, but was there for 179 days
  • Shows that the sleep/wake cycle is trained in by exogenous zeitgebers
• Circadian Rhythm-

  Aschoff and Wever 1976-

  • Had a group spend 4 weeks in a WW2 bunker with no natural light
  • All but 1 (29hrs) had a circadian rhythm of 24-5 hours
  • Suggesting that the sleep wake cycle is longer than 24 hours, but forced to be 24 hours through endogenous zeitgebers
• Circadian Rhythm-

  Folkard 1985-

  • 12 people who lived in a dark cave for 3 weeks
  • Sleeping when the clock said 11:45pm, waking at 7:45am
  • Researchers gradually sped up the clock secretively, so their days became 22 hours
  • Only 1 participants could comfortably adjust
  • Suggesting that there’s a strong free running circadian rhythm that’s hard to over come with exogenous zeitgebers
• Circadian Rhythm-

  CPS- Boivin (1996)- people who work night shifts, then have heavily reduced concentration at 6AM

  CPS- Knutsson (2003)- more likely to develop hart disease/poor health than those who have a regular/natural sleep wake cycle

  CPW- Solomon (1993)- night shift workers have more divorces due to missing family events, causing strain
• Circadian Rhythm-

  S- Used to help medical treatments - body’s functions rise and fall throughout the sleep wake cycle, aspirin is more effective to prevent heart attacks when taken at night, due to them being more likely in the mornings – Bonten (2015)

  W- Hard to generalise due to normally being based off of small samples, and the cycles diffrent that’s between people

  W- Czeisler found it varied 13-65 hours

  W- Siffre 1999 found that his own sleep wake cycle has slowed from his youth.