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RHYTHMS…read more

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What are biological rhythms?
They're recurring changes in the way biological
systems behave.
e.g. The sleep wake cycle (people sleep when its
dark and wake up when its light)
This cycle is controlled by
Endogenous pacemakers (internal biological clocks
e.g. Hormone levels)
Exogenous Zeitgebers (external cues in the
environment e.g. Light)…read more

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What is a circadian rhythm?
Circadian rhythms are rhythms that last for
approximately 24 hours ­ i.e. A day
The 2 best examples : sleep-wake cycle and
body temperature cycle…read more

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The Sleep Wake cycle
You might think we go to sleep at regular times just because of
changes in daylight
i.e. Are sleepy when its dark and awake when its light
Or maybe its because we know what time of day it is?
These are all external cues that are definitely important in guiding the
sleep-wake cycle
But there is also an internal circadian clock that's free running and
has a cycle of around 24-25 hours long.
In normal circumstances this cycle doesn't just work on its own
because there are external cues e.g. The sunlight that help adjust
this internal circadian clock to the environment you live in.
Studies show that circadian rhythms persist despite isolation from
natural light which shows there is an endogenous clock (internal).
The research also shows that external cues are important because
the endogenous clock wasn't accurate and varied from day to day.…read more

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Michael Siffre
Michael siffre stayed in caves over long time periods
where he had no external cues (no radio, clock or
daylight). He simply woe, ate and slept when he felt like
First Stay: he stayed in the underground in the alps for 61
days. He came out on September 17th thinking it was
August the 20th
Second Stay: he stayed for 6 months in a cave in Texas.
His Circadian rhythm settled at just over 24 hours but
sometimes would dramatically change to 48 hours.
Third Stay: He was 60 and wanted to see the affects of
age on the Circadian rhythm. He found that his
sleeping patterns changed and that his internal clock
was slower.…read more

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Evaluating Michael Siffre
Aschoff and Wever supported his study with their findings.
His study might be described as a case study as it's the study
of one person so has unique features.
His body's behaviour might not be typical for everyone else's
behaviour and also the fact that he chose a cave (might
have been cold) may have effected his rhythms.
However studies made above ground have supported his
Siffre's study was also an experiment so the key variables
were controlled. This allowed him to completely demonstrate
a causal relationship.…read more

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