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Biological Rhythms
Circadian Rhythms:
Once in 24 hours! ­ E.g. Sleep/Wake Cycle
­ E.g. Temperature
Infradian Rhythms:
Less than 24 hours! ­ E.g. Menstrual Cycle
Ultradian Rhythms:
More than once a day! ­ E.g. Sleep Stages…read more

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Endogenous Pacemakers
Endogenous Pacemakers are internal pacemakers.
Mammals mainly rely on the Suprachiasmatic Nucleus
Morgan: Removed the SCN from Hamsters, and found their
circadian rhythms disappeared. The rhythm could be re-
established using transplanted SCN cells. The mechanism
underlying this is based on an interaction between FOUR proteins.
Biological Rhythms are also endogenously regulated by
hormones (as in the Menstrual Cycle)…read more

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Exogenous Zeitgebers
Exogenous Zeitgebers are External Pacemakers.
Miles et al: Studied a blind man who had a 24.9 hour circadian
rhythm despite being exposed to Zeitgebers that should have
resulted in a 24 hour rhythm. He relied on stimulants to regulate
his sleep wake cycle. This demonstrates that Light is the dominant
Light has been shown to be the dominant Zeitgeber.
However, its affects can be overcome:
Luce and Segal: Noted that individuals who live in the Arctic Circle
still sleep for about 7 hours despite the sun never setting. In this
case, it is social cues that are dominant.…read more

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Disrupting Rhythms
(Shift Work)
Shift Work:
On average it takes 3 days to adjust to a 12 hour shift in time. Artificial
lighting is moderately effective in re-setting the circadian rhythm, but it
takes time. Performance is affected because some body clocks are
slower to reset, meaning the rhythms are desynchronised.
Individual Differences:
Reinberg et al: Those people whose circadian rhythms change least may
cope best overall.
Harmful Effects: May be caused by other factors. E.g. Shift workers
suffer from sleep deprivation, and are more prone to depression.…read more

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Disrupting Rhythms
(Jet Lag)
Jet Lag:
Klein et al: Found that adjustment was easier for westbound flights
(phase delay)
Schwartz et al: Found that East Coast US Baseball teams did better
when travelling West than West coast teams travelling East. Showing
that Phase Delay has less effect.
Redfern: Suggested the use of Benzodiazepines to increase Melatonin
levels and resynchronise the body clock.
Webb and Agnew: Interviewed regular travellers and found they used
various non-pharmacological approaches to minimise the impacts.…read more

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