endogenous pacemakers and exogenous zeitgebers

• Endogenous pacemakers


  Internal factors that maintain the sleep/wake cycle
• Exogenous zeitgebers


  External factors that reset the biological clock
• Suprachiasmatic nucleus


  • Primary endogenous pacemaker in maintaining sleep/wake cycle
  • Receives information about light from the optic chiasm
• Animal studies of SCN: Destroyed SCN connections in chipmunks, sleep/wake cycle disappeared and majority were killed by predators
• Pineal gland


  Increases melatonin during the night
• Melatonin


  Induces sleep and may cause Seasonal Affective Disorder (SAD)
• Light


  Resets the SCN, influences hormone secretion and blood circulation
• Participants woken and light shone on back of knees and chest produced a deviation of 3 hours in cycle
• Social cues


  Influence sleep/wake cycle, e.g. determined meal times and bedtimes in adults
• Circadian rhythms begin at 6 weeks old
• Adapting to local times of eating and sleeping helps overcome jet lag
• Endogenous pacemakers


  Internal biological clocks
• Exogenous zeitgebers


  External time cues
• Animal studies on ethics are problematic as animals cannot be generalised to humans
• Chipmunks were harmed and at great risk when returned back to their natural habitat
• Exogenous zeitgebers can be overstated
• A blind man had a circadian rhythm of 24.9 hours that could not be adjusted
• The blind man had to take sedatives at night and stimulants in the morning
• Interactionist system


  The interaction between endogenous pacemakers and exogenous zeitgebers
• Only in exceptional circumstances are endogenous pacemakers unaffected by exogenous zeitgebers
• Siffre's cave studies lack validity as they are rare and do not reflect real life situations where the two factors interact