endogenous pacemakers and exogenous zeitgebers Flashcards
endogenous pacemakers
internal biological clocks, free-running/ naturally occurring
Exogenous Zeitgebers
external changes in the environment
endogenous pacemakers study AO2 - DeCoursey et al
They destroyed SCN connections in the Brians of 30 chipmunks, then were returned to their natural habitat and observed for 80 days. Their sleep/ wake cycle disappeared and many were killed by predators.
This supports the idea that the SCN is the primary endogenous pacemaker.
endogenous pacemakers study AO2 - Ralph et al
He bred ‘mutant’ hamsters with a 20 hour sleep/ wake cycle. SCN cells were transplanted from the foetal tissue of these hamsters into the brains of normal hamsters, which then developed cycles of 20 hours. This shows how the sleep/ wake cycle is innate and determined by the SCN.
this demonstrates the SCN as a key endogenous pacemaker and supports the idea that it regulates the sleep/ wake cycle, that also shows its innate.
melatonin is an endogenous mechanism: sleep/wake cycle
Low levels of light
Melanopsin (sensitive to light) on the retina detects the low levels of light - LVf-RH, RVF-LH
SCN in the hypothalamus receives the information from the optic nerve
Sends signal to the pineal gland
Increases melatonin
Induces sleep
exogenous Zeitgebers AO2 study - Campbell and Murphy
woke 15 participants at various times and some a light on the backs of their knees - producing a deviation in the sleep/ wake cycle of up to 3 hours. This shows light doesn’t necessarily rely on the eyes to influence the SCN.
this supports exogenous zeitgebers because it demonstrates how the exogenous zeitgeber light can disrupt sleep.
endogenous pacemakers AO3 - limitation, SCN research may obscure other body clocks
body clocks are found in many organs and cells and are highly influenced by the SCN, but can act independently
Camilla at al showed how changing g feeding patterns in mice altered circadian rhythms of cells in the liver for up to 12 hours - leaving SCN unaffected
suggests there may be other complex influences of the sleep/ wake cycle aside from the SCN
endogenous pacemakers AO3 - limitation, they can’t be studied in isolation
only in exceptional circumstances are endogenous pacemakers free running and unaffected by the influence of exogenous zeitgebers
in every day life pacemakers and zeitgebrs interact so it may make little sense to separate the 2 in studies
suggests the more researchers attempt to isolate the influence of internal pacemakers, the lower the validity of research
endogenous pacemakers AO3 - limitation, ethics
animal studies of the sleep/ wake cycle are justified because there are similar mechanisms in a ll mammals, so generalisations can be made to the human brain
however, there are ethical issues. animals were exposed to considerable risk on Decoursey et al’s study and most died as a result
suggests that studies like these cannot be justified and researchers should find alternative ways of studying endogenous pacemakers
exogenous Zeitgeber AO3 - limitation, the effects differ in different environments
EZs do not have the same effect on people who live. in places where there is very little darkness un the summer and very little light in the winter
the Innuit Indians of the Artic circle have sim earl sleep patterns all year round, despite spending around 6 months in darkness
suggests the sleep/ wake cycle is primarily controlled by endogenous pacemakers that can override environmental changes in light
exogenous Zeitgeber AO3 - limitation, c case study evidence undermines the effects of exogenous cues
Mile set al reported the case of a man, blind from birth, with an abnormal circadian rhythm of 24.9 hours. despite exposure to social cues such as meal times, his sleep/ wake cycle couldn’t be adjusted
suggets that social cues alone are not effective in resetting the biological rhythm and the natural body cock is stronger
exogenous Zeitgeber AO3 - limitation, age-related insomnia
natural chan ges in circadian rhythms mean older people fall asleep early and have poorer quality of sleep
however, Hood et al found that management of insomnia improved if elderly people were more active and had more exposure to natural light during the day
suggest that exogenous changes in lifestyle may be just as likely to cause age-related insomnia as internal biological changes
