exogenous zeitgebers & endogenous pacemakers

• What is an endogenous pacemaker?

  Internal body clocks that regulate many of our biological rhythms.
• What are exogenous zeitgebers?

  External cues that may affect or entrain our biological rhythms, such as the influence of light on the sleep/wake cycle.
• What is the main endogenous pacemaker in the human body?

  suprachiasmatic nucleus, (SCN)
• What is the SCN referred to as?

  Our master clock
• What is the SCN (suprachiasmatic nucleus)?

  A tiny cluster of nerve cells in the hypothalamus
• What does the SCN obtain information about?

  Light
• Where does the SCN obtain this information about light from?

  The optic nerve
• what does he SCN do with this information?

  signal the pineal gland to increase melatonin at night
• what doe melatonin do?

  Induce sleep
• What are examples of exogenous zeitgebers?

  Light, social cues and temperature
• What is the most dominant zeitgeber in humans?

  Light
• what can light do to the SCN?

  Reset it
• What key processes does light have an indirect influence on?

  Hormone secretion and blood circulation
• In the absence of light, what does temperature become?

  The dominant zeitgeber
• What does cold temperature signal? What about war,?

  Cold temperature - time for reduced activity

  Warm temperature - time for activity
• What type of system are the exogenous zeitgebers and endogenous pacemakers?

  A blended system
• What is a weakness of endogenous pacemakers and exogenous zeitgebers? (Individual differences)

  P - Studies have demonstrated differenecs within human bodily rthyms.

  
  

  E - Studies of individuals who live in the Arctic regions (where the sun does not set during the summer months) show normal sleep patterns despite the prolonged exposure to light.

  
  

  T - This suggests that there may be occasions when exogenous zeitgebers (external cues) may have little bearing on our internal rhythm. This is known as 'free running' - where the biological clock operates in the absence of any external cues.
• What is a strength? (Animal studies - decoursey et al 2000)

  P - Animal studies provide research support for the role of endogenous pacemakres.

  
  

  E - DeCoursey et al. (2000) Removed the SCN in 30 chipmunks (a lesion was made so that the SCN was no longer connected). The chipmunks were returned to their natural habitat and observed alongside 'normal' chipmunks. After 80 days, significantly more of the SCN-lesioned chipmunks had been killed by weasels.

  
  

  T -This was presumably because these chipmunks remained awake and vulnerable when they should have been asleep. This study emphasises the role of the SCN in establishing and maintaining the sleep/wake cycle.
• What is another strength? (Research from Morgan)

  P - Further research comes from Morgan (1995)

  
  

  E - Morgan bred 'mutant' hamsters so they had circadian rhythms of 20 hours instead of 24 hours, and then transplanted their SCNs into normal hamsters. The normal hamster then displayed the mutant rhythms.

  
  

  T - This study again emphasises the role of the SCN in establishing and maintaining the sleep/wake cycle
• P) natural changes in circadian rhythms means older people fall asleep early and have poorer quality sleep (Duffy et al).

  E) however, hood et al found that management of insomnia improved if elderly people were more active and had more exposure to natural light during the day.

  T) this suggests that exogenous changes in lifestyle may be just as likely to cause age related changes in insomnia as internal biological changes