ENDOGENOUS PACEMAKERS & EXOGENOUS ZEITGEBERS

• What is our body clock and how is it controlled?

  our internal body clock (endogenous pacemaker) is controlled and reset by external cues in the environment (exogenous zeitgebers)
• what are exogenous zeitgebers?

  external time cues that our bodies can detect and use to keep the internal clock in sync with the outside world

  known as entrainment
• what would happen without entrainment?

  we would be running on a 25 hour cycle as seen in the free running experiments
• what is the main EZ?

  light
• how do social cues act as an EZ?

  schedules such as set meal times and bedtimes help newborns settle into a circadian rhythm

  adapting to local times for eating and sleeping beats jet lag
• what is the SCN?

  superchiasmatic nucleus - primary endogenous pacemaker
• what is the SCN made up of?

  tiny bundle of nerve cells in the hypothalamus which helps maintain rhythms
• where does the SCN lie?

  just above the optic chiasm (where optic nerves cross over) and receives information about light from this structure
• what does the SCN control?

  the sleep/wake cycle
• what was Ralph (1990) procedure to test the SCN influence?

  bred ‘mutant hamsters with 20 hour sleep wake cycle.

  SCN cells from mutant hamsters were transplanted into brains of normal hamsters

  cycles in the second group defaulted to 20 hours
• what was the conclusion of Ralph’s study?

  the SCN has an important role in establishing and maintaining the circadian sleep/wake cycle
• what was DeCoursey (2000) procedure?

  destroyed the SCN connections in the brains of 30 chipmunks

  returned the chipmunks to their natural habitat and observed them for 80 days
• what were the findings of DeCoursey’s experiment?

  the sleep wake cycle had disappeared

  a significant proportion of chipmunks had been killed by predators
• what was the conclusion of DeCoursey’s experiment?

  SCN is very important to the sleep/wake cycle. it gives us a evolutionary advantage
• where does the SCN pass information to?

  the pineal gland
• what does the pineal gland do?

  increases the production of melatonin during the night
• what does melatonin do?

  hormone that induces sleep and is inhibited during periods of wakefulness
• how did Campbell and Murphy study light and EZ’s?

  woke 15 participants at various times and shone a light on the back of their knees, producing a deviation of the sleep/wake cycle of up to three hours
• what do Campbell and Murphy’s findings tell us?

  light is a powerful exogenous zeitgeber detected by the skin receptor sites and does not necessarily rely on the eyes to influence the SCN
• strengths of research

  practical and real life application - knowledge of the importance of light in sleeping and wakefulness has lead to useful advice and products eg dawn simulation alarms or smart bulbs
• limitations of research into SCN

  may obscure other body clocks - they are found in many organs and cells but can act independently of the SCN. research showed that changing feeding patterns in mice altered CR in the liver but not SCN. suggests may be other complex influences on the sleep/wake cycle

  Use of Animal Studies - issue in generalising findings, ethical problems
• limitations of EZ research

  influence may be overstated - people in artic regions (where sun doesn’t set in summer, doesn’t rise in winter) show normal sleep patterns despite exposure to light at all times

  Methodological Issues - Campbell and Murphy’s study is yet to be replicated, criticised as may have been light exposure to eyes (major confounding variable)

  EP and EZ’s interact with each other - makes no sense to separate them for research purposes, unrealistic