biological rhythms - circadian rhythms Flashcards
what are biological rhythms governed by
- endogenous pacemakers (internal biolocgical ‘clocks’)
- exogenous zeitgebers (external changes in environment)
how long do circadian rhythms last
around 24 hours
examples of circadian rhythms
eg. sleep/wake cycle, core body temperature
describe the sleep/wake cycle
- effect of day light = important exogenous zeitgeber & can reset the SCN
- governed by endogenous pacemaker = suprachiasmatic nucleus (SCN)
- SCN sits just above optic chiasm providing info from eye about light
outline siffre’s cave study
- spent several extended periods of time underground in caves
- deprived of natural light/sound but access to food/drink
- resurfaced in mid september (1962) after 2 months in caves in southern alps thinking it was mid-august
- ‘free-running’ biological rhythm settled to one just beyond 24 hours (roughly 25 hours) though fell asleep & woke up on regular schedule
outline study by aschoff & wever (1976)
- group of participants spent 4 weeks in WW2 bunker deprived of natural light
- all but 1 participant displayed circadian rhythm between 24-25 hours
- suggests (alongside siffre) that sleep/wake cycle may be slightly longer than 24 hours but it’s
entrained by exogenous zeitgebers associated with 24-hour day
research on sleep/wake cycle (circadian rhythm)
- siffre
- aschoff & wever (1976)
- folkard et al. (1985)
outline study by folkard et al. (1985)
- studied 12 people who lived in dark cave for 3 weeks, retiring to bed when clock said 11.45pm & woke when it said 7.45am
- researchers slowly sped up clock so a believed 24 hour day became 22 hours
- only 1 participant could comfortably adjust
- suggests existence of strong free-running circadian rhythm which cannot be easily overridden by exogenous zeitgebers
AO3 +) research providing understanding of adverse consequence when circadian rhythms are disrupted (desynchronisation)
-) studies investigating effects of shift work often use correlational methods
E:
- boivin et al. (1996) found night workers who engaged in shift work experienced a period of reduced concentration around 6am (circadian trough) meaning mistakes/accidents were more likely
- research also showed relationship between shift work/poor health - shift workers 3x more likely to develop heart disease than those with typical work patterns (knutsson 2003)
T: shows research into sleep/wake cycle may have real-world economic implications to best manage worker
productivity
HOWEVER: studies investigating effects of shift work often use correlational methods
- difficult to establish whether desynchronisation of sleep/wake cycle is cause of negative effects
- solomon (1993) concluded high divorce rates in shift workers may be due to strain of deprived sleep & other influences (eg. missing out on family events)
T: suggests it may not be biological factors which create adverse consequences associated with shift work
AO3 +) research into circadian rhythms has been used to improve medical treatments
- circadian rhythms coordinate many basic bodily processes (eg. heart rate, digestion) which rise & fall during course of day
- this led to field of chronotherapeutics
- eg. aspirin (treat heart attacks) is most effective when taking last thing at night as reduces blood platelet activity which reduces risk of heart attack & heart attacks most likely to happen in the morning
- supported by bonten et al. (2015)
T: shows circadian rhythm research can help increase effectiveness of drug treatment
AO3 -) generalisations are difficult to make from research
- studies use small samples of participant & sleep/wake cycles may vary between people
- czeisler et al. (1999) found individual differences in sleep/wake cycles varying 13-65 hours
- duffy et al. (2001) revealed some people have natural preference for sleeping early/rising early (‘larks’) & vice
versa (‘owls’)
T: means it is difficult to use research data to discuss anything more than averages due to individual
differences
