Summary
Summary circadian rhythms
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notes for biopsych aqa a level psychology
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Biological rhythms: circadian rhythmsBiological rhythms are periodic activity governed by:
- Internal biological clocks (endogenous pacemakers)
- External changes in the environment (exogenous zeitgebers)
Ultradian rhythm – occurs many times during the day. (Stages of sleep)
Infradian rhythm – takes longer than a day to complete. (Menstrual cycle)
Circadian rhythm – lasts about 24 hours. (Sleep wake cycle)
Sleep wake cycle
Exogenous zeitgebers – fact we feel drowsy when it’s night-time and alert during the day
shows effect of daylight.
Endogenous pacemakers – suprachiasmatic nucleus (SCN) in the hypothalamus that lies
above the optic chiasm and provides info from the eye about light.
Siffre’s cave study:
- He lived underground (in dark cave) for 2 months and then later 6 months to test the
internal body clock
- Deprived of exposure to natural light and sound
- His circadian rhythm settled down to 25 hours.
- Suggesting endogenous pacemakers entrain the circadian rhythm to just short of
natural.
Folkard et al (1985):
- Showed endogenous pacemakers are stronger than exogenous zeitgebers.
- Convinced a group of 12 to live in a cave, they went to sleep at 11:45pm and got up at
7:45am
- Researchers slowly sped up the clock to be just 22 hours.
- Only 1 participant was able to easily adjust.
- Suggests the existence of a strong free running circadian rhythm not controlled by
exogenous zeitgebers (external factors).
Evaluation
Practical application
- Application to shift work.
- Bolvin et al found shift workers have a dip in concentration around 6am (a circadian
trough) causing accidents to be more likely.
- Knutsson et al found it 3x more likely for shift workers to develop heart disease.
- Research into the sleep wake cycle may have economic implications in terms of how to
best manage shift work.
Real world application to medical treatment
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