endogenous pacemakers and the SWC

Question 1

what are endogenous pacemakers?

Answer 1

internal body clocks that regulate many of our biological rhythms

Question 2

what is the suprachiasmatic nucleus (SCN)?

Answer 2

• bundle of nerve cells in hypothalamus of each hemisphere
• primary mammalian EP
• influential in maintaining circadian rhythms eg. SWC

Question 3

how does the SCN maintain the SWC?

Answer 3

• nerve fibres connected to the eye cross optic chiasm on their way to left and right visual area of cerebral cortex
• SCN lies just above optic chiasm
• receives info about light directly from this structure
• this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst asleep

Question 4

animals studies and the SCN: decoursey et al. (2000)

Answer 4

• destroyed SCN connections in brains of 30 chipmunks
• then returned to their natural habitat and observed for 80 days
• SWC disappeared
• by the end of the study, a significant proportion had been killed by predators, presumbaly as they were awake and vulnerable to attack when they should have been asleep

Question 5

animals studies and the SCN: ralph et al. (1990)

Answer 5

• bred ‘mutant’ hamsters with a 20h SWC
• when SCN cells from foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycles of the 2nd group defaulted to 20h

Question 6

pineal gland

Answer 6

• SCN passes info on day length and light that it receives to the pineal gland (just behind hypothalamus)
• another EP guiding SWC
• during the night, the pineal gland increases production of melatonin

Question 7

melatonin

Answer 7

• chemical that induces sleep and is inhibited during periods of wakefulness
• suggested as a causal factor in SAD

Question 8

evaluation: SCN research may obsure other body clocks

Answer 8

• research has revealed there are numerous circadian rhytms in many organs and cells in the bod
• these peripheral oscillators are found organs including the lungs, pancreas and skin
• they are influenced by the actions of the SCN but also act independently
• damiola et al. (2000) demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours whilst leaving the rhythm of the SCN unaffected
• this suggests other complex influences on the SWC
• too reductionist to assume only SCN plays role?

Question 9

evaluation: endogenous pacemakers cannot be studied in isolation

Answer 9

• total isolation studies, such as siffre’s cave study, are extremely rare
• siffre also used artificial light which could have reset his biological clock everytime he turned in it on
• in everyday life, pacemakers and zeitgebers interact
• it may make little sense to separate the two for the purpose of research
• the more researchers attempt to isolate the influence of internal pacemakers, the lower the validity of the research

Question 10

evaluation: ethical issues justified

Answer 10

• animal studies of SWC are justified as there are very similar mechanisms across species
• existence of SCN and pineal gland in the brains of chipmunks and hamsters means generalisations can be made to the human brain, as the mammalian brain has similar structures

Question 11

evalution: disturbing ethical issues

Answer 11

• animals in decoursey et al.’s study were exposed to risk when returned to their natural habitat
• most died as a result
• cannot generalise to humans as our brains are more complicated so research is not justified?