endogenous pacemakers and exogenous zeitgebers Flashcards
what is the suprachiasmatic nucleus
tiny bundle of nerve cells located in hypothalamus in each hemisphere of brain
one of primary endogenous pacemakers in mammalian species and it influential in maintaining circadian rhythms
nerve fibres connected to eye cross in an area called optic chaism on their way to the left anf right visual area of cerebral cortex
scn lies just above optic chiasm
received info about light directly from this structure
continues when our eyes close enabling biological clock to adjust to changing patterns of daylight while we are asleep
what are animal studies and the scn
influence of scn demonstrated in studies involving animals
decoursey destroyed scn connections in brains of 30 chipmunks who were returned to natural habitat and observed 80 days
sleep wake cycle of chipmunks disappeared by the end of the study a signf proportion of them had been killed by predator
ralph bred mutant hamsters with 20 hour sleep wake cycle
when scn cells from foetal tissue of hamsters transplanted into brains of normal hamsters the cycles of second group deafulted to 20hrs
what is the pineal gland and melatonin
scn passes info on day length and light that it receives to the pineal gland
another endogenous mechanism guiding the sleep wake cycle
during night pineal gland increases production of melatonin chemical that indcues sleep ad inhibited during periods of wakefulness
melatonin suggested causal factor in season affective disorder
what are exogenous zeitgebers
external factors in environment that reset biological clocks through process known as entrainment
in absence of external cues free running biological clock controls the sleep wake cycle continues to tick in distinct cyclical pattern
free running cycle brought into link by environmental cues so there is interaction of internal and external cues
explain light effect
light key zeitgeber
can reset bodys main endogenous pacemakes plays a role in maintenance of sleep wake cycle
light indirect influence on key processes in body that control functions such as hormone secretion and blood circulation
campbell and murphy demonstrated light may be detected by skin receptor sites on the boody even when the same info not received by the eyes
15 pps woekn at various times and light pad was shone on back of knees
researchers managed to produce deviation in pps sleep wake cycle of up to 3 hours in some cases
suggests light powerful exogenous zeitgeber that need not necessarily rely on the eyes to exert influence on the brain
what are social cues
babies seldom on same sleep wake cycle as rest of family
newborn babies initial sleep wke cycle random
6 weeks of age circadian rhythms begin and 16 weeks rhythms have been entrained by schedules imposed by parents including adult determined mealtimes and bedtimes
research on jet lag suggests adpating to local times for eating and sleeping effective way of entraining circadian rhythms and beating jet lag when travelling long distances
what is beyond the master clock
scn may obscure other body clocks
research revealed that there are numerous circadian rhythms in many organs and cells in body
peripheral oscilators found in organs including lungs pancreas and skin
influenced by the actions of scn but act independently
damiola demonstrated how changing feeding patterns in mcie could alter circadian prhythms of cells in liver by up to 12hrs whilst leaving the rhythm of scn unaffected
suggests other complex influences on sleep wake cycle
what is the interactionist system
endogenous pacemakers cant be studied in isolation
total isolation studies extremely rare
siffre made use of artificial light which could have reset his biological clock everytime he turned his lamp on
pacemakers and zeitgebers interact may make little sense to separate the two for the purpose of research
suggest more researchers attempt to isolate the influence of internal pacemakers the lower the validity of the researcher
what are ethics
animal studies justified because similar mechanisms at work across species
existence of scn and pineal gland in brains of chipmunks and hamsters means generalisations can be made to human brain as mammalian brain has similar structures
more disturbing issue ethics involved
animals in decoursey study exposed to risk when returned to natural habitat and died as result
what is environmental observations
exogenous zeitgebers dont have same effect in all environments
experience of people who live in places where very little darkness in summer and very little light in winter tell different story from usual narrative
people who live in arctic circle similar sleep patterns all year round despite spending 6 months in total darkness
suggests sleep wake cycle primarily controlled by endogenous pacemakers that can override environemtnal changes in light
what is case study evidence
evidence challenges role of exogenous zeitgebers
miles recount study of young man blind from birth who had abnormal cirdaian rhythm of 24.9hrs
despite exposure to social cues such as regular mealtimes his sleep wake cycle couldnt be adjusted
suggests social cues alone not effective in resetting biological rhythm
what is age related insomnia
evidence suggest people poorer quality sleep as they get older
might be due to natural changes in circadian rhythm as we age means falling asleep earlier and broken sleep at night
studies suggested exogenous factors may be more responsible for changes in sleep patterns amongst older people
hood found management of insomnia improved if elderly people more active and had more exposure to natural light
