sleep-wake cycle

• what controls the sw cycle?

  endogenous pacemakers (internal factors)

  
  

  exogenous zeitgebers (external factors)
• endogenous pacemakers

  internal body clock

  
  

  regulates many of our biological rhythms

  
  

  e.g. influence of the SCN on the SW cycle
• SCN

  suprachiasmatic nucleus
• SCN

  bundle of nerve cells in hypothalamus

  
  

  primary endogenous pacemaker

  
  

  maintains circadian rhythms
• the SCN receives info about light levels

  through the optic nerve

  
  

  automatically adjusts internal clock according to the light outside

  
  

  passes on info about day length and light to pineal gland (increases prod. of melatonin - inducing sleep)
• SCN - extra detail

  connected to the eye are nerve fibres

  
  

  these cross at an optic chiasm while on their way to the visual area of the cerebral cortex

  
  

  SCN is located above the optic chiasm so receives information about light directly from this structure, even when our eyes are closed, allowing our bio clocks to adjust to changing daylight while we are asleep
• exogenous zeitgebers

  ext factors in our environments that can reset our biological clocks

  
  

  Siffre proved our clocks tick in the absence of external cues

  
  

  =SW cycle determined by an interaction of int and ext factors
• outline and explain another exogenous zeitgeber

  social cues

  
  

  in infants, circ rhythms begin at 6 weeks

  
  

  schedules imposed by parents influence the babies (i.e. mealtimes, bedtimes)

  
  

  adapting to local times for sleeping and eating (rather than eating when you're hungry/tired - effective way of entraining circadian rhythms)
• outline and explain one exogenous zeitgeber

  light

  
  

  can reset the main endo pacemaker (SCN)

  
  

  affects SW cycle

  
  

  influences key processes that control functions e.g. hormone secretion and blood circulation
• DeCoursey et al


  CHIPMUNKS

  
  

  destroyed SCN connections in brains of 30.

  
  

  returned to habitat and observed for 80 days

  
  

  lost their SW cycle and as a result, lots were killed by predators as they were awake when they should've been asleep (= vulnerable to attack)

  
  

  example of ENDOGENOUS PACEMAKERS (internal body clock)
• decoursey eval

  ethical issues with using animals - chipmunks died, was this ethically justifiable?

  
  

  limitations of using animal studies - can't generalise findings well to humans due to differences in physiology = low ecological validity - difficult to extrapolate findings of basic chipmunks to complex humans
• ralph et al `


  HAMSTERS

  
  

  bred mutant hamsters to have circ rhythms of 20 hours instead of the usual 24

  
  

  SCN neurons from mutants transplanted into normal hamsters

  
  

  these then took on a rhythm of 20 hours

  
  

  = significance of SCN and that endo pacemakers are important for bio rhythms
• campbell and murphy


  light can be detected by skin receptors on the body even if not detected by the eyes themself

  
  

  15 ppts woke at various times after having light shone on the back of their knees

  
  

  some ppts SW cycle was disrupted by up to 3 hours
• c and m evals

  yet to be replicated

  
  

  methodology and lack of controls criticised by other psychologists (eyes can still detect changes in light even when closed - acts as a confounding variable )

  
  

  - reduction in validity of findings - low internal validity
• Miles et al


  man blind since birth had a sleep wake cycle of 24.9 hours

  
  

  could not have his cycle adjusted adjusted by any external factors, e.g. social cues

  
  

  had to take sedatives at night and stimulants in the morning to adjust 24 hours world

  
  

  = weakens influence of exogenous zeitgebers on biological rhythms
• evals

  influence of exo zeitgebers may be overstated because of studies like miles (external factors did not help in adjusting his cycle)
• research has revealed there are numerous circadian rhythms in many organs and cells of the body

  called peripheral oscillates, found in: adrenal gland, windpipe, liver, lung, etc.

  
  

  Damiola et al demonstrated that changing feeding patterns in mice could alter circadian rhythms of the cells in the liver by up to 12 hours, while leaving the rhythm of the SCN unaffected

  
  

  = other complex influences on SW cycle asides apart from master clock (SCN) - we shouldn't be reductionist
• research into the effect of exogenous zeitgebers such light has practical applications

  Burgess et al

  
  

  found exposure to bright light over 3 days decreased jet lag

  
  

  exposure to bright light prior to an east to west flight decreased the time needed to adjust to local time

  
  

  3 test group variations:

  
  

  continuous light - shifted circ rhythm by 2.1 hours

  
  

  intermittent light - shifted circ rhythms by 1.5 hours

  
  

  dim light - shifted circadian rhythm 0.6 hours

  
  

  
  

  = intensity of light affected sleep