Endogenous pacemakers and exogenous zeitgebers

• Endogenous pacemakers:

  • suprachiasmatic nucleus receives information about day light and length of day from the eyes, processed by visual area in occipital lobe.
• • SCN’s process this info and triggers different rates of release of melatonin from pineal gland.
  • increased melatonin triggers decrease serotonin production creates feelings of sleepiness.
  • during day , high exposure to light SCN’s triggers the pineal gland to release less melatonin increases serotonin during the day for wakefulness.
• Exogenous zeitgebers:

  • Has social cues that entrain biological rhythms. Include set meal times, bed times which signify when to wake up and when to fall asleep = means to avoid jet lag, useful to accustom to set sleeping and eating times of destination to avoid dsynchronisation of an already ‘pre-set’ circadian rhythm.
• De Coursey (research):

  • surgically lesioned SCN of 30 chipmunks compared their circadian rhythm in natural habitat with 17 controls.
  • found vast majority of experimental group had been killed within first 30 days after being returned to their habitat.
  • Nocturnal movement detected within permanent dens by radio telematic data logging, especially suprachiasmatic nucleus lesioned animals.
• Siffre (research):

  • completed cave study investigating exogenous zeitgebers on sleep wake cycle (such as light).
• Miles et al (research):

  • reported case of a man with a sleep wake cycle, could not be changed through the use of either stimulants or sedatives.
• Campbell and Murphy (research):

  • produced deviations of 3hours in ppt sleep wake cycle by shining light onto pads on back of knees, to showlight not always need to be detected by eyes to entrain biological rhythm.
• Weakness:

  • P - influence of the SCN‘s may be overestimated.
  • ex - Damiola et al - circadian rhythm on mice live cells could be influenced to experience a 12h discrepancy , leaving SCN’s unaffected.
  • Exp - ‘peripheral oscillators‘ present in the adrenal gland and lungs, are collections or systems of cells which act independently of SCN, having own biological rhythm.
• Weakness:

  • P - considerable ethical issues with the case of animals.
  • Ex - De Coursey, although doesnt impact upon validity analyses would have to be conducted to assess whether such ethical costs outweigh research.
• Weakness:

  • P - can’t generalise findings from animal studies to humans .
  • ex - due to differences in psychology and types of circadian rhythm.
  • L - limits ecological validity
• Weakness:

  • P - recorded cases where exogenous and endogenous pacemakers:
  • Ex - Miles et al who reported the case of a man with a sleep wake cycle, could not be changed through use of sedatives or stimulants.
  • L - exogenous and endogenous may be overestimated.