the effect of endogenous pacemakers & exogenous zeitgebers Flashcards
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 to adjust to daylight when our eyes open and close
What are endogenous pacemakers?
Internal body clocks that regulate many of our biological rhythms. For example , influence of melatonin on the sleep/wake cycle
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
How is the Beyond the master clock (SCN) a strength of endogenous pacemakers?
- 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
- suggests there may be other complex influences on the sleep/wake cycle
- suggesting circadian rhythms can act independently of the SCN
What research did Damiola et al (2000)
how changing feed patterns in mice could alter circadian rhythm of cells in the liver by 12 hours
- rhythms of SCN unaffected
How is ethics in animal studies a weakness of endogenous pacemakers?
- 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
How is the Interactionist system a weakness of endogenous pacemakers?
- 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
What are 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 human
- can reset the main endogenous pacemaker (SCN)
- plays a role in the sleep/wake cycle
- has an indirect effect on hormone secretion & blood circulation
What research did Campbell and Murphy (1998) do on the effect on light?
- 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
How is aged related insomnia can be treated by zeitgebers a strength of the effect of exogenous zeitgebers?
- 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
How are environmental observations a weakness of the effect of exogenous zeitgebers?
- 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
