endogenous pacemakers & exogenous zeitgebers Flashcards
endogenous pacemaker of sleep/wake cycle
- suprachiasmatic nucleus (SCN) located in hypothalamus in each hemisphere
- primary endogenous pacemaker & influential in maintaining circadian rhythms (eg. sleep/wake cycle)
- nerve fibres connected to eye cross optic chiasm to left/right visual area of cerebral cortex
- SCN lies just above optic chiasm & receives info about light directly from this
which study demonstrates influence of suprachiasmatic nucleus (SCN)
decoursey et al. (2000)
research by decoursey et al. (2000)
- destroyed SCN connections in brains of 30 chipmunks, returned to natural habitat & observed for 80 days
- sleep/wake cycle was destroyed
- by end of study, significant proportion had been killed by predators (awake/active when should’ve been asleep)
role of pineal gland & melatonin as endogenous pacemaker
- SCN passes info on day length/light to pineal gland
- endogenous mechanism guiding sleep/wake cycle
- during night, pineal gland increases melatonin production (suggested as causal factor in SAD)
endogenous pacemakers: AO3 -) SCN research may obscure other body clocks
E:
- research revealed there’s many circadian rhythms in organs/cells in the body
- eg. peripheral oscillators found in organs (such as lungs, pancreas, skin) & they’re influenced by actions of SCN but also act independently
- damiola et al. (2000) showed how changing feeding patterns in mice could alter circadian rhythms of cells in liver by up to 12 hours, whilst leaving rhythm of SCN unaffected
T: suggests other complex influences on sleep/wake cycle
endogenous pacemakers: AO3 -) endogenous pacemakers can’t be studied in isolation (interactionist system)
E:
- total isolation studies (eg. siffre’s cave study) are rare
- siffre still used artificial light which could’ve reset his biological clock when lamp turned on
- in everyday life, pacemakers/zeitgebers interact & it may make little sense to separate 2 when researching
T: suggests as more researchers attempt to isolate influence of internal pacemakers, the lower the validity of the research
define exogenous zeitgebers
external factors in environment which reset biological clocks (entrainment)
describe light as an exogenous zeitgebers
- can reset body’s main endogenous pacemaker (SCN) = plays key role in maintenance of sleep/wake cycle
- has indirect influence on key processes in body which control functions (eg. hormone secretion, blood circulation)
what did campbell & murphy (1998) show
= light may be detected by skin receptor sites on body
- 15 participants woken at various times & light pad shone on back of their knees
- researchers produced deviation in participants usual sleep-wake cycle of up to 3 hours
- suggests light is powerful exogenous zeitgeber which doesn’t always rely on eyes to exert influence on brain
exogenous zeitgebers - social cues
- babies sleep/cycle are rarely the same as family
- at ~16 weeks, babies rhythms are entrained to schedule imposed by parents
- research on jet lag suggests adapting to local times for eating/sleeping is effective way of entraining rhythms & beating jet lag if travelling far
exogeneous zeitgebers: AO3 -) evidence to challenge to role of exogenous zeitgebers
E:
- miles et al. (1977) described the study of a young man, blind from birth, who had abnormal circadian rhythm of 24.9 hours
- despite exposure to social cues (eg. regular mealtimes), his sleep/wake cycle couldn’t be adjusted
T: suggests social cues alone aren’t effective in resetting biological rhythm
exogeneous zeitgebers: AO3 -) exogenous zeitgebers don’t have same effect in every environment
E:
- experience of those who live in places with little darkness in summer/little light in winter are different
- eg. those living in artic circle have similar sleep patterns all-year, despite spending roughly 6 months in darkness
T: suggests sleep/wake cycle is primarily controlled by endogenous pacemakers which can override environmental changes (eg. light)
