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Biological Rhythms & Sleep

Biological Rhythms
Research studies into Circadian, Ultradian &
Infradian rhythms, including the role of
endogenous pacemakers and exogenous
The consequences of disrupting biological
rhythms (for example shift work, jet lag)
Sleep States
The nature of sleep
Functions of sleep, including evolutionary
explanations & restoration theory…

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A bodily rhythm is defined as `a cyclical variation over some period of time in
physiological or psychological processes'.

There are 3 rhythms in humans, they are:

Circadian (Around 24 hours) (Day & Night)
Infradian (More than 24 hours) (Menstrual Cycle)
Ultradian (Less than 24 hours) (Sleep Stages)

Research Studies…

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wiped under the noses of
the other 20 women.
Results McClintock concluded that
68% of the women
responded to the
pheromones. Pheromones
collected from the women
during the early period of
their cycle shortened the
other women's cycle from
1-14 days to 1-12 days.
Conclusion It's unclear if the

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The Ultradian rhythm is the rhythm with a frequency of less than 24 hours.
Using a number of techniques we've learnt that sleep is composed of several
repetitive cycles lasting around 90 minutes each.

There are also 3 ways sleep is measure:

The Electroencephalogram (EEG) - Measures brain activity

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In humans and mammals the internal circadian clock is located in the
Suprachiasmaticnucleus (SCN) which is at the bottom of the brain near the
hypothalamus. The SCN is based on a 24 hour clock that uses light from the
optic nerve to reset it. Evidence for the SCN being the…

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The SCN sits just above the optic nerve where vision begins to get processed.
It seems that light acts to modify the natural clock in the SCN. It is suggested
that light in the morning resets the system.

Miles et al (1977) reported on a man who was blind from…

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during the night and sleep during the day. And day time sleeping may be of a
lower quality compared to night time sleep.

There are 2 types of Shift Work:

1. Non-fluctuating, where workers work unconventional hours but they
don't change
2. Fluctuating, where workers work eight hours shifts that…

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internal clock that's out of sync with the external environment. DSPS sufferers
are able to get plentiful sleep; it is just delayed compared to normal times.


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