endogenous pacemakers and exogenous zeitgebers Flashcards
what is the SCN?
-Located in hypothalmus in each hemipshere
-primary endogenous pacemaker
-infulences maintaining circadian rythms such as sleep wake
how do nerve fibres connected to the eye cross
-optic chiasm on their way to the left and rught visual area of cerebral cortex
-SCN lies above optic chiasm
-recieves info ab light from this structure
even when eyes are closed
-biological clock adjusts changing patterns of daylight whilst we r asleep
what did coursey et al do?
-destroyed SCN connection in brains of chipmunks who returned to natural habitat and observed for 80 days
what did coursey et al find?
-huge proportion were killed by predetors
-as they were awake whilst meant to be asleep
so vulnerbale to attack
what did ralph et al do?
-bred mutant hamsters
-20 hr sleep wake cycle
-when SCN from foetal tissue of mutant hamsters were transplanted to normal brains, their cycle defualted to 20 hrs
what is another endogenous mechanism in the sleep wake cycle?
-pineal gland produces melatonin a chemical inducing sleep and inhibited during periods of wakefulness
-cause of SAD
weaknesses of endogenous pacemakers
(beyond the master clock)
-there may be numerous circadian rythms in many organs
-these are peripheral oscillators in lungs, pancreas, skin
-can be infulenced by SCN but also act indpendantly
-damilola et al showed= changing feeding patterns in mice can alter circadian rythm of cells in liver by up to 12 hrs when leaving SCN unaffected
(interactionist system)
-endogenous pacemakers cant be studied alone
-siffre cave study= made use of artifical light
which could have re set his biological clock
-pacemakers and zeitgebers can interact
-little sense to seperate the two for research
-to seperate the 2 would lower validity
how can we comment on the ethics of research?
-the animals in de coursey et al study were exposed to risk when returned to their natural habitat and most actually died
what role does light play in sleep wake cycle
-its a zeitgeber
-resets interal body clock
-infulence on hormone secretion and blood circualtion
how can we comment on social cues?
-new born babies intial sleep wake cycle is random
-6 weeks of age- the circadian rythms begin
-at around 16 weeks schedules imposed by parents e.g mealtimes
what study did campbell and murphy carry out
-demonstrated light can be detected by skin receptors
-15 Ps woken up at various times and light pad shone at back of knees
-deviaiton occured in sleep wake cycle up to 3 hrs at times
-so light is powerful exogenous zeitgeber
what is the research on jet lag
-adapting to local times for eating and sleeping is an effective way of entraining circadian rythms and beating jet lag when travelling long distance
what are the weaknesses zeitgebers
(environmental observations)
-dont have same effect everywhere
-those in arctic circle have similar sleep patterns all yr round despite spending 6 mnths in total darkness
-sleep wake cycle is primarily controlled by endogenous pacemakes that overrude environmental changes in light
(case study evidence)
-miles et al recount the story of man with abnormal circadian rythm of 24.9hrs
-even with social cues his sleep wake cycle couldnt be adjusted
how can we talk about age related insomnia?
-ppl have poorer sleep as they get older
-due to natural changes in circadian rythm so fall asleep earlier and broken sleep at night
-hood et al found mangement of insomnia improved if elderly people were generally more active and had more exposure of light
