endogenous pacemakers and exogenous zeitgebers

• What are endogenous pacemakers?

  Internal mechanisms that govern biological rhythms, in particular the circadian sleep/wake cycle
• What is the most important endogenous pacemaker in the sleep wake cycle?

  The suprachiasmatic nucleus
• The suprachiasmatic nucleus lies where in the brain?

  The hypothalamus
• The suprachiasmatic nucleus receives information about what?

  Light levels (an exogenous zeitgeber) from the optic nerve
• The suprachiasmatic nucleus then sends a message where?

  The pineal gland
• If light levels are low, what does the pineal gland do?

  Release melatonin, helping to induce sleep
• What did DeCoursey et al. (2000) do?

  Destroyed the SCN connections in the brains of 30 chipmunks, returned

  them to their natural habitat and observed them for 80 days
• What did DeCoursey et al. (2000) find?

  The sleep/wake

  cycle disappeared and a significant proportion of them had been killed by

  predators.
• What did Ralph et al. (1990) do?

  Bred "mutant" hamsters with a 20 hour sleep/wake cycle.
• What did Ralph et al. (1990) find?

  When SCN cells

  from the foetal tissue of mutant hamsters were transplanted to normal

  hamsters, the normal hamsters default to 20 hour sleep/wake cycle.
• How does light affect our sleep/wake cycle?

  Light levels are detected by the SCN. At levels of low light, the SCN sends signals to the pineal gland which increases production of melatonin which helps us sleep
• What did Campbell and Murphy (1998) do?


  15 participants were woken at various times and light was shone on the

  back of their knees.
• What did Campbell and Murphy (1998) find?

  Their sleep cycle changed by up to 3 hours in some cases.
• What do the results of Campbell and Murphy (1998) show?

  This suggest that light is a power exogenous zeitgeber that doesn't need the eyes of exert an influence on the brain
• What kind of social cues may affect our sleep/wake cycle?


  Meal times, bed times and social activities.
• What did Klein and Wegmann (1974) find?

  The circadian rhythms of travellers adjusted more quickly if they went outside more at their destination
• What explanation did Klein and Wegmann (1974) provide for their results?

  This was thought to be because they were exposed to the social cues of their new time zone
• What did Klein and Wegmann (1974) suggest as an effective way of beating jet lag?

  Adapting to local times

  for eating and sleeping