ENDOGENOUS PACEMAKERS

• Mechanisms within the body e.g. internal body clocks that regulate our biological rhythms, such as the influence of the SCN on the sleep-wake cycle. 
• The suprachiasmatic nucleus (SCN)


  The SCN is a tiny cluster of nerve cells which are in the hypothalamus of both hemispheres and is influential in maintaining the circadian rhythm such as the sleep-wake cycle. It acts as a master clock, controlling other biological rhythms. The SCN receives information about light from the optic chasm, continuing even when our eyes are closed. 
• Decoursey et al (2000)

  • They destroyed the SCN on 30 chipmunks and returned them to their natural habitat for an observation for 80 days 
  • Most of them had been killed as their sleep/wake cycle had been destroyed so they were more susceptible to predators and being hunted. 
• Ralph et al

  • Wanted to investigate the influences the SCN has on hamsters 
  • They took the SCN out of genetically abnormal hamsters with a circadian rhythm of 20 hours and transplanted them into hamsters with the usual 24-hour cycle 
  • Normal hamster cycles shortened to 20 hours, suggesting that the SCN helps to maintain the regular sleep wake cycle 
• Evaluation

  ❌Too simplistic to suggest that the SCN is the only endogenous pacemaker – there are others external to the SCN that have a circadian rhythm, acting independently from the SCN – other complex influences aside from the SCN. 

  ❌Endogenous pacemakers cannot be studied in isolation – cases such as Sifre's cave study are extremely rare – better to adopt a more interactionist approach to understand how endogenous pacemakers and exogenous zeitgebers work together.