endogenous pacemakers & exogenous zeitgebers

• endogenous pacemaker

  -internal factors/processes/body clocks that regulate biological (circadian) rhythms
• Suprachiasmatic nucleus (SCN)

  -the master body clock

  -located in the brain, above the optic nerve

  -regulates biological rhythms; regulates the pineal gland that produces melatonin production
• exogenous zeitgebers

  External factors/processes that help regulate biological rhythms. Signal for internal processes to happen.
• Ralph et al (1990)

  -looked at the impact of EPs on biological rhythms

  -bred mutant hamsters - they had a s/w cycle of 20h

  -transplanted SCN cells from their foetal tissues to normal hamsters

  -these normal hamsters s/w cycle changed to 20h

  -EPs are crucial in regulating biological (circadian) rhythms
• DeCoursey et al (2000)

  -looked at the effects of SCN as an EP

  -destroyed the SCN connections in 30 chipmunks, put them back in their natural environment and observed them for 80 days

  -their s/w cycle disappeared, lots of them were killed by predators

  -SCN is a vital EP in the s/w cycle
• main exogenous zeitgebers for the sleep/wake cycle

  -light levels: signal the body to start/reduce production of melatonin

  -social cues e.g., routines, time (clock), food
• Campbell & Murphy (1998)

  -looked at light as an EZ on the sleep/wake cycle

  -15 ppts woken up at different times in the night & had a light pad shone on the back of their knee

  -the light produced a deviation in ppts sleep/wake cycle by 3 hours

  -light is a critical EZ for the sleep/wake cycle

  -light is absorbed by skin receptor sites, don't rely on the eyes
• exogenous zeitgebers - AO3

  Strength(s):

  -Miles et al (1997): blind man couldn't regulate sleep/wake cycle despite social cues. Shows that light is a critical EZ. Increases validity.

  
  

  Weakness(es):

  -EZs don't have the same effect in every environment. People who live in the Arctic Circle (little dark in summer, little light in winter) have a similar s/w cycle all year. EP might be more important than EZ. Decreases validity.