the effect of endogenous pacemakers & exogenous zeitgebers

• endogenous pacemakers


  Internal body clocks that regulate many of our biological rhythms. For example , influence of melatonin on the sleep/wake cycle
• How does the suprachiamatic nucleus (SCN) affect the body?

  - it is a tiny bundle of nerve cells in the hypothalamus in each hemisphere

  - one of the main endogenous pacemakers in mammals and influences the sleep/wake cycle

  - nerve fibres connected to the eye cross over in an area called the optic chiasm ( on the way to the visual area of the cereal cortex) which lies just above

  - it receives information about light (optic chiasm) even when our eyes are closed which allows biological clock to adjust to daylight when our eyes open and close
• How does animal studies and the SCN affect the body?

  - Decoursey et al (2000) = destroyed the SCN connections in 30 chipmunks who were returned to their natural habitat and were observed for 80 days

  - their sleep cycle disappeared and by the end many were killed by predators as they were awake when they should have been asleep

  - Ralph et al (1990) = bred mutant hamsters with a sleep/wake cycle of 20 hours

  - when the SCN cells from foetal tissue of these hamsters were transplanted into the the brain of the normal normal hamsters ( had a cycle of 20 hours)

  - these highlight the role of SCN in the sleep/ wake cycle
• How does the pineal gland and melatonin affect the body?

  - SCN passes the information relating to the day length and light to the pineal gland

  - at night the pineal gland produces more melatonin
• AO3: Beyond the master clock (SCN) (strength)

  - many circadian rhythms around the body (called peripheral oscillators and found in the adrenal glands , oesophagus , liver , lungs , pancreas , spleen , thymus and skin)

  - these are highly influenced by the SCN but can act independently

  - Damiola et al (2000): studied how changing feed patterns in mice could alter the circadian rhythm of cells in the liver by 12 hours but the rhythms of SCN was unaffected

  - suggests there may be other complex influences on the sleep/wake cycle

  - suggesting circadian rhythms can act independently of the SCN
• AO3: ethics in animal studies (weakness)

  - ethical implications of the DeCoursey study

  - chipmunks were harmed and put at risk when returned to their natural habitat

  - debate whether what we learn justifies the unethical procedures

  - issues with making generalisations to human
• AO3: interactionist system (weakness)


  - only exceptional circumstances that endogenous pacemakers are free-running and unaffected by exogenous zeitgebers

  - even research by *Siffre is extremely rare and could be considered lack internal validity

  - in reality, pacemakers & zeitgebers interact and it makes little sense to separate them
• exogenous zeitgebers


  External cues that affect or entrain our biological rhythms. For example, the influence of light and social cues on the sleep/wake cycle
• How does light affect the body?

  - key zeitgeber in humans

  - can reset the main endogenous pacemaker (SCN)

  - plays a role in the sleep/wake cycle

  - has an indirect effect on hormone secretion & blood circulation
• Campbell and Murphy (1998): effect of light on the body


  - demonstrated that light may be detected by skin receptor sites on the body even the same information isn't received by the eyes

  - 15 people woken at various times during the night , a light was shone on the back of their knees

  - produced a deviation in their usual sleep/wake cycle (up to 3 hours in people)
• What did the research Campbell and Murphy do suggest?

  suggesting that light is a powerful exogenous zeitgeber that doesn't necessarily rely on the eyes to influence the brain
• How does social cues effect the body?

  - newborns have a random sleep/wake cycle

  - by 6 weeks old - circadian rhythm begins

  - by 16 weeks old - most babies are entrained

  - causation of this

  - could be routines imposed by parents are likely to influence this ( feeding times , bath times , bed times etc) - social cues

  - suggested that adapting to local times of eating and sleeping when travelling abroad ( rather than responding to our own tiredness and hunger) is the best way to beat jet lag

  - as exogenous zeitgebers help our body to get back to normal
• AO3: aged related insomnia can be treated by zeitgebers (strength)


  - older people have poorer quality of sleep due to natural changes in the sleep/wake cycle as they age

  - this could be improved if elderly people were generally more active & had more exposure to daylight
• AO3: environmental observations (weakness)


  - they don't have the same affect in the same environment

  - people who live in the Arctic have similar sleep patterns all year round (despite spending 6 months in darkness)

  - suggests that the sleep/wake cycle may be controlled by endogenous pacemakers that can override the influence of light

  
  

  Miles et al (1977): - male subject (blind since birth) had a circadian rhythm of 24.9 hours

  - despite being exposed to social cues , his sleep/wake cycle could not be adjusted

  - had to take sedatives at night and stimulants in the morning to maintain a 24 hour cycle