Biological Rhythms Flashcards
What is a biological rhythm?
Cyclical changes that influence the way body behaves
Always restarts within a certain time frame.
Evolutionary
What is a circadian rhythm?
Lasts 24 hours
Regulates physical processes.
Driven by body clocks
Synchronised by SCN in hypothalamus
What is the SCN?
Master pacemaker
Must be constantly reset to be kept in synch.
Sensitive to light
What are endogenous pacemakers?
internal body clock that keep biological processes to time.
What are exogeneous zeitgebers?
External cues that alter body clocks to match environment
e.g: light, social cues
Describe briefly how sleep/wake cycle works?
Exogenous zeitgeibers
—> light resets SCN
When light detected by SCN, it sends light to the pineal gland which stops production of melatonin.
Describe study of Siffre in the cave?
Suggested that endogenous pacemakers are free-running and maintain cycles without constant entrainment of exogenous zeitgebers.
Spent 6 months in a cave with no natural light or social cues.
Findings of Siffre’s study
The body clock maintained regular cycle of around 25 hours without EZs
Suggested that biological clock free-running but to keep it at 24 hours —> needs entrainment
Criticism of cave study
Use of artificial lights disrupted measurements of free-running circadian rhythm by acting as an EZ.
Czeisler found circadian rhythm closer to 24 hours when controlling for artificial light.
Ralph (1990) evidence SCN = EP
Switched circadian rhythm of normal hamsters with mutant hamsters (20hr)
Both gained each others sleep wake cycle
Suggests SCN = main endogenous pacemaker in sleep-wake cycle
Vetter (2011)
27 office workers in experimental group exposed to strong blue light
Shift circadian rhythm to match office lighting
Control group = matched to natural light of dawn
Suggests light = EZ
Artificial light = disrupt endogenous pacemaker by over-riding natural light as primary EZ.
—> more people exposed to blue light = technology (phones + LED)
Provides advice on how to maintain healthy sleep pattern
Social cues as EZ?
Social cues less effective as exogenous zeitgeiber compared to light
Miles (1977)
Man blind from birth even with social cues had 24.9 hour circadian rhythm —> sleep out of synchronisation with rest of society
Evaluation points
Positive implications to wider society —>medical effectiveness
Better to take aspirin at night.
provides understanding of negative consequences of desynchronisation.
Night shift workers 3x more likely to get heart disease.
Reduced concentration = more likely to make mistakes
