Rhythms

• Endogenous pacemakers


  Mechanisms within the body that govern the internal biological bodily rhythms (eg, sleep wake cycle / suprachiasmatic nuclei)
• Exogenous Zeitgebers


  An environmental cue (light or social) that helps to regulate the biological clock in an organism
• Circadian rhythm


  A pattern of behaviour that occurs approximately every 24 hours, which is set by exogenous Zeitgebers
• Suprachiasmatic Nuclei

  The master circadian rhythm pacemaker which is found in the hypothalamus that receives light information

  Light - optic nerve - SCN - Pineal gland (produces melatonin) = sleep wake cycle
• How is the sleep wake cycle maintained

  • Homeostasis system tries to maintain homeostasis through noting changes and energy dips
  • Even with absence of EZs the internal body clock is still 24-25 hours
  • Internal and external factors combine to enable us to keep rhythm and adjust to changes
  • However, because light entrains our rhythms we struggle with tasks like night work
• Michael Siffre cave study (1962)

  • Subjected himself to extended periods underground to investigate his own circadian rhythms
  • Absence of EZ’s - light, clock, radio
  • Woke, ate, and slept when he felt like it

  1. 61 days underground - lost track of days and months
  2. 6 months underground - CR was just over 24 hours
  3. When he got older, his CR was 48 hours
• Strength - Role of SCN

  • Morgan (1995) mutant hampster - genetic breeding of hampsters with 20 hour rhythm, removed SCN’s and transplanted into normal hampsters who displayed 20 hour rhythms
• Strength - Real world application

  • Burgess et al (2003) - exposure to a bright light prior to a flight decreased the time needed to readjust to local time on arrival. shifts rhythm, up to 2 hours
• Weakness - Seperated rhythms

  • Kate Aldcroft spent 25 days in a lab with no EZs. She played ‘amazing grace’ at the same time everyday and her rhythm slipped to 30 hours
• Strength/weakness - How do blind people develop circadian rhythms

  • Skene and Arendt (2007) estimated most blind people still have some light perception. The pathway from retinal cells controlling melanopsin to SCN is still intact
• Circadian rhythm strength - Real World Application

  Development of Chronotherapeutics - timing of drug therapy

  • Timing of drug treatment has significant impacts on treatment success
  • Drugs can be taken hours before release in order to time the treatment the most effectively
  • EG, heart attacks mostly take place about an hour after waking up, so drugs taken at 10PM can be released at 6AM
• Circadian rhythm - individual differences

  • Length of cycles varies - 13-65 hours (Czeislar et al 1999)
  • Cycle onset - morning or evening people
• Circadian rythms strength/weakness - research methodology

  • Confoudning variables?
  • Artifical light?
  • One ppt?
• Entrainment - exogenous Zeitgebers resetting the SCN