Pacemakers Flashcards
What is an endogenous pacemakers?
An internal body clock that regulates our biological rhythms
Give an example of an endogenous pacemaker
The SCN (Suprachiasmatic nuclei)
Explain the role of the SCN
Light passes through the SCN and this info is passed onto the pineal gland.
At night the lack of light increases the production of melatonin
Melatonin induces sleep
When the darkness ends and the sunlight passes through the SCN, the production of melatonin from the pineal gland decreases.
Give evidence into the role of the SCN
DeCoursey et al (2000): The SCN connections were destroyed, in the brains of 30 chipmunks who were then returned to their natural habitats and observed for 80 days.
They found that the sleep/wake cycle had disappeared for the chipmunks & by the end of the study a significant proportion of them had been killed by predators.
Evidence: Ralph et al (1990)
Bred mutant hamsters with a 20 hour sleep wake cycle
When SCN cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycles of second group defaulted to 20 hours.
Evaluate the ethical issues associated with animal studies
Particularly in the DeCoursey et al study, the animals were exposed to considerable harm as well as subsequent risk when they were returned to their natural habitat
The insights gained from animal studies justifies the harm they were subjected to is heavily debated.
What is an exogenous zeitgebers?
External cues that may affect our biological rhythms.
They interact and work with our endogenous pacemakers and can reset our biological clock (this is known as entrainment)
Explain light as an exogenous zeitgebers
Light can reset the body’s main endogenous pacemaker (the SCN)
Light also has an indirect influence on processes in the body that control hormone secretion and blood circulation
Explain social cues as a zeitgebers
In infants, the initial sleep/wake cycle is random. At 6 weeks of age the circadian rhythm begins and at 16 weeks most infants are entrained.
The schedules imposed by parents have an influence including mealtimes and bedtimes
Explain research into the influence of light
Campbell & Murphy(1998)
They aimed to investigate the extent to which light influences the sleep wake cycle.
15 participants were used in this study and they were woken up at various times in the night. A light pad was shone on the back of their knees. They found this created a deviation of their sleep - wake cycle of up to 3 hours.
This proves that light is a powerful exogenous cue and it doesn’t need to be received through the eyes to influence our brain and affect our biological rhythms.
Evaluate the methodological issues with Campbell & Murphy’s research
Other psychologists have been critical of the manner in which the study was conducted. It suggests these may have been some limited light exposed to the participants eyes which was the confounding variable.
By receiving light directly through the eyes this could be argued to influence the results thus leading to a disruption of the sleep/wake cycle.
Also isolating one exogenous zeitgeber in this way doesn’t give us insight into the many other zeitgebers that influence the sleep/wake cycle
Evaluate the supporting research for endogenous pacemakers
There is supporting research of the idea that endogenous pacemakers influence our circadian rhythms especially the sleep/wake cycle.
Suffer conducted his study being in a cave for several months where he was deprived of exposure to natural light and sound. They discovered that his free running biological rhythm was 25 hours which supports the idea that the SCN is responsible for our regular biological rhythms.
Evaluation: An Interactionist System
Research that sees endogenous pacemakers and exogenous zeitgebers separately have been criticised for lacking validity.
This is because only in exceptional circumstances are endogenous pacemakers free running and Not affected by exogenous.
Studies such as Siffre’s Cave study could be judged as lacking validity for this reason. In real life pace makers and zeitgebers interact and it may make little sense to separate the two for the purpose of research.
