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Biological Rhythms Topic 1…read more

Slide 2

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The Sleep Wake Cycle AO1
The sleep wake cycle is controlled by the internal clock as well as by
exogenous zeitgebers
Multiple studies show the sleep wake cycle exists when people are isolated
from external cues
Michael Siffre studied it by staying in caves for long time periods without
radios, clocks or light
He simply ate, slept and woke up when he felt like it in order to establish
how long his circadian rhythms are
1962 Alps for 61 days
1975 Texas cave for 6 months.
Rhythms settled at 24 hours
1999 Aged 60 ­ rhythm had slowed…read more

Slide 3

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The Sleep Wake Cycle AO2
It's a case study
His research isn't valid because his behaviour is untypical of all
Studies Were in caves so the cold may have affected his findings
Siffres findings are supported by studies that were conducted over
This support was an experiment where variables were controlled…read more

Slide 4

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The Sleep Wake Cycle AO2
Siffre used dim lighting
When the research was conducted they didn't
believe that dim lighting would affect circadian
Czeisler (1999) ­ found he could change circadian
rhythms up to 28 hours long or down to 22 hours
long…read more

Slide 5

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The Sleep Wake Cycle AO2
The explanations for circadian rhythms are
They suggest that the sleep wake cycle is determined
by internal mechanisms
The internal clock is powerful and this is illustrated by
a study of a blind man who's circadian rhyhms couldn'
t be changed by any other factors such as lights or
clocks but his rhythms remained at 24 hours
However people can simply choose to sleep earlier or
wake up later…read more

Slide 6

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The Core Body temperature cycle
Body temperature changes throughout the day
18: 04:
00 30
Body temperature peaks at 6pm which makes
us tired
Body temperature is at its lowest at 4:30am
which makes us awake…read more

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