endogenous pacemakers and exogenous zeitgebers

Question 1

what are the 5 biological rhythms?

Answer 1

•endogenous pacemakers
•exogenous zeitgebers
•circadian rhythm
•infradian rhythm
•ultradian rhythm

Question 2

what are exogenous zeitgebers?

Answer 2

external cues that may affect or entrain our biological rhythms, such as the influence of light on the sleep/ wake cycle (the sun)

Question 3

what are endogenous pacemakers?

Answer 3

internal body clocks that regulate many of our biological rhythms, such as the influence of the supreachiasmatic nucleus (SCN) on the sleep/ wake cycle

Question 4

spell the SCN

Answer 4

the suprachiasmatic nucleus

Question 5

where is the SCN located?

Answer 5

in the hypothalamus

Question 6

what is the SCN?

Answer 6

one of the primary endogenous pacemakers and it is influential in maintaining circadian rhythms such as the sleep/ wake cycle

Question 7

what area do the nerve fibres connected to the eye cross in?

Answer 7

the optic chiasm

Question 8

what does the SCN lie above?

Answer 8

the optic chiasm

Question 9

how does the SCN help regulate our sleep/ wake cycle?

Answer 9

•optic nerves cross over in the optic chiasm
•the SCN is a ‘bundle’ of nerves that sits above the place where the optic nerves cross over in the optic chiasm, it’s main function is to detect light
•this then sends a signal to the pituitary gland, which sends a message to the pineal gland
•the pineal gland is either in the sympathetic or parasympathetic state
•when less light is detected, the pineal gland produces melatonin, which sends the body to sleep
•when light is detected in the morning, the pineal gland stops producing melatonin and the body wakes up

Question 10

what was DeCoursey’s chipmunk study?

Answer 10

•DeCoursey gathered 30 chipmunks and sliced out their SCN, then released them back into the wild.
•Their sleep/ wake cycle had disappeared by the end of the study and a significant proportion had been killed as they were out at night
•this shows the importance of the SCN to survival

Question 11

what was Ralph’s ‘mutant’ hamster study?

Answer 11

•Ralph bred mutant hamsters with a 20 hour sleep/wake cycle and when the SCN cells from the hamsters were implanted into foetal hamsters, they also defaulted to a 20 hour sleep/wake cycle
•this emphasises the role of the SCN in establishing and maintaining the circadian sleep/wake cycle

Question 12

what are the main two exogenous zeitgebers?

Answer 12

sunlight and social cues

Question 13

what study was done into light as an exogenous zeitgeber?

Answer 13

Campbell and Murphy collected 15 participants and woke them at various times and a light pad was shone on the back of their knees. researchers managed to produce a deviation in the participants usual sleep/wake cycle of up to 3 hours in some cases. this suggests that light is a powerful exogenous zeitgeber that need not necessarily rely on the eyes to exert its influence on the brain

Question 14

what is evidence for social cues being prominent exogenous zeitgebers?

Answer 14

new born babies do not have the same sleep/ wake cycle as the rest of the family. schedules imposed by parents are likely to be a key influence in establishing the cycle, including adult- determined mealtimes and bedtimes

Question 15

evaluation of the significance of the SCN

Answer 15

+animal studies
-beyond the master clock
-ethics in animal studies
-influence may be overstated
-methodological issues in studies
-interactionist system

Question 16

strength: animal studies

Answer 16

studies like DeCoursey’s and Ralph’s show the importance of the SCN in survival and maintaining sleep cycles, which could be applied to real life scenarios

Question 17

limitation: beyond the master clock

Answer 17

•research has found that there are numerous circadian rhythms in many organs and cells of the body, these are called peripheral oscillators
•these can act independently of the SCN
•Damiola demonstrated how changing feeding patterns in mice could alter circadian rhythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SCN unaffected.
•This suggests that there may be many other complex influences on the sleep/ wake cycle, aside from the ‘master clock’ (the SCN)

Question 18

limitation: ethics and generalisability

Answer 18

•findings cannot always be generalised from animals to humans
•in DeCourseys study the animals were exposed to harm and risk when they were returned to their natural habitat, with many of them dying
•ethically and morally wrong

Question 19

limitation: influence of exogenous zeitgebers may be overstated

Answer 19

•Miles recount the story of a young man, blind from birth, but with a circadian rhythm of 24 hours
•despite exposure to social cues, his sleep/ wake cycle could not be adjusted
•similarly individuals who live in arctic regions show normal sleep patterns despite the long exposure to light
•both these examples suggest that there are occasions when exogenous zeitgebers may have little bearing on our internal rhythm

Question 20

limitation: methodological issues

Answer 20

•findings from the Campbell and Murphy study are yet to be replicated
•other psychologists are critical and suggested that there may have been some light exposure to the participants eyes, which is a major confounding variable
•also, excluding one exogenous zeitgeber (light) does not give us insight into the many other zeitgebers that influence the sleep/ wake cycle, and the extent to which these may interact

Question 21

limitation: interactionist system

Answer 21

•only in exceptional circumstances are endogenous pacemakers free-running and unaffected by the influence of exogenous zeitgebers
•total isolation studies, like Siffre’s cave studies, could be judged as lacking validity for this reason
•in real life, pacemakers and zeitgebers interact, and it may make little sense to separate the two for the purpose of research