endo pacemakers exo zeitgebers

• Endogenous Pacemakers


  Internal body clocks that regulate our biological rhythms
• Exogenous Zeitgebers 


  External cues that influence and reset our internal biological clocks
• Suprachiasmatic nucleus (SCN)


  A tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain
• What does the SCN do?

  • It is an example of a endogenous pacemaker that sets the timing of when we need to sleep
  • The SCN regulates the pineal gland that releases melatonin which helps us sleep
• Animal Research and the SCN

  • In 30 chipmunks their SCN was destroyed and they were returned to their natural habitat for 80 days
  • At the end the chipmunks lost their sleep wake cycle and many were killed by predators
• Give an example of an endogenous pacemaker

  The SCN
• Give examples of exogenous zeitgebers

  Light and Social cues
• Light

  • Helps reset the SCN
  • Light also has an indirect influence on hormone secretion and blood circulation
  • In a study light was detected by skin receptor sites even when not detected by the eyes
  • It can influence the sleep wake cycle
• Social Cues

  • A 6 weeks of age circadian rhythms start and babies' rhythms have been entrained by the schedules imposed by parents
  • This is through mealtimes and bedtimes
  • Research on jet lag suggests adapting to local times for eating and sleeping is an effective way of entraining circadian rhythms and beating jet lag
• AO3 Endogenous Pacemakers: Research support from Shiffre

  • Shiffre's cave study shows how we have internal body clocks that regulate our sleep wake cycle
  • This is due to how he managed to have a sleep wake cycle of around 25 hours despite having no natural light
• AO3 Endogenous Pacemakers: Interactionist System

  • Endogenous Pacemakers cannot be studied in isolation
  • Shiffre's cave study was really rare and he also used artificial light which could have reset his biological clock
  • Pacemakers and zeitgebers interact
  • The more researchers attempt to isolate the influence of internal pacemakers the lower the validity of the research
• AO3 Endogenous Pacemakers: Ethics

  • Animal studies on the sleep wake cycle are justified because they have similar mechanisms
  • The existence of an SCN and pineal gland in the brains of animals means that generalisations can be made to humans
  • However the chipmunk study resulted in many of them dying which was extremely unethical
• AO3 Exogenous Zeitgebers: Case study evidence

  • Evidence challenge the role of exogenous zeitgebers
  • A young blind man from birth had an abnormal circadian rhythm of 24.9 hours
  • Despite exposure to social cues such as regular mealtimes the sleep wake cycle could not be adjusted suggesting social cues are not effective in resetting biological rhythms
• AO3 Exogenous Zeitgebers: Age related insomnia

  • Evidence suggests that people have poorer quality sleep as they get older due to natural changes in the circadian rhythm
  • Exogenous factors may be more responsible for the changes in sleep patterns amongst older people
  • Insomnia is improved if you were more active and exposed to light
• AO3 Exogenous Zeitgebers: Research against

  • 12 people were in a dark cave for 3 weeks going to bed at 11:45 and waking up at 7:45 and the researchers gradually sped up the clock
  • The 24 hours day only lasted 22 hours
  • Only one person could comfortably adjust to the new schedule
  • The existence of a strong circadian rhythm cannot easily be overridden by exogenous zeitgebers