Endogenous pacemakers + exogenous zeitgebers

• Endogenous pacemaker

  Internal body clocks that regulate our biological rhythms
• Exogenous zeitgeber

  External factors that affect or entrain our biological rhythms\
• Suprachiasmatic nucleus

  Bundle of nerve cells located in the hypothalamus of each hemisphere.

  A primary endogenous pacemaker as it is influential in maintaining circadian rhythms such as the sleep/wake cycle.

  SCN lies above optic chiasm.

  Receives information about light enabling the biological clock.
• Animal studies -SCN

  DeCoursey et al

  destroyed SCN connections in the brains of 30 chipmunks who were then returned to their natural habitat.

  Sleep/wake cycle of the chipmunks disappeared.

  Significant proportion killed by predators. - awake at night when vulnerable to attack.
• Counterpoint - animal studies SCN

  Not generalisable to humans
• Limitation - SCN research alters other body clocks.

  Damiola et al

  Changing feeding patterns in mice could also alter circadian rhythms of cells in the liver by up to 12 hours, SCN left unaffected
• Light as an exogenous zeitgeber

  Key zeitgeber as it can reset the body's main endogenous pacemaker - SCN.

  Maintenance of sleep/wake cycle.

  Campbell + Murphy

  • light may be detected by skin receptor sites on the body that is not the eyes.
  • 15 participants woken up at various times and light pad shone on back of knees.
  • Produced deviation in sleep/wake cycle
• Social cues

  Baby's rhythms entrained by schedules imposed by parents.

  Research on jet lag, adapting to local times for eating and sleeping entrains the circadian rhythm
• Limitation - EZ, case study

  Miles et al

  Study of man blind from birth with a circadian rhythm of 24.9 hours.

  Sleep/wake cycle not adjusted even with social cues.
• Limitation - EZ, not same effect in all environements

  People who live in places with little darkness in summer and little light in winter.

  e.g. Arctic circle.

  Similar sleep-patterns all year round.