endogenous and exogenous

• what is an endogenous pacemaker

  a mechanism that governs internal biological rhythms
• what is referred to as the master time keeper?

  the SCN in the hypothalamus
• how does the SCN work?

  it receives light from the optic chasim allowing our biological clock to adjust to changing patterns of light
• what did Decoursy do?

  destroyed the SCN of 30 chipmunks then returned them to their natural habitat - their sleep wake cycle had disappeared after 80 days and most had been killed by predators as they were awake at night
• what does the pineal gland do?

  releases melatonin at night
• strength of endogenous pacemakers

  • Morgan bred hamsters with SCNs of 20 hours. the SCN of these were put into normal 24 hour hamsters and their sleep wake cycle changed to 20 hours. - powerful influence
• strength of endogenous pacemakers

  • Siffre - powerful influence ( go back to circadian rhythms)
• what are exogenous zeitgebers referred to as?

  time keepers
• what are exogenous zeitgebers?

  - environmental cues that help regulate the biological clock
• what is the key zeitgeber for humans

  light
• what did cambell and murphy do?

  15 ppts were awoken at various times by light being shone into the backs of their knees - deviation of 3 hours in their sleep wake cycle - light is powerful
• what are other exogenous cues?

  temp, social cues
• at how many weeks do babies become trained in their sleep wake cycle?

  16
• weakness of exogenous zeitgebers

  • their influence may be exaggerated- people in arctic regions show normal patterns of sleep despite extended exposure to light - may be more influenced by endogenous pacemakers