Biological Rhythms

· Research studies into Circadian, Ultradian & Infradian rhythms, including the role of endogenous pacemakers and exogenous zeitgebers

· The consequences of disrupting biological rhythms (for example shift work, jet lag)

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Biological Rhythms & Sleep
Biological Rhythms
Research studies into Circadian, Ultradian &
Infradian rhythms, including the role of
endogenous pacemakers and exogenous
zeitgebers
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
Lifespan changes in sleep
Disorders of sleep
Explanation of insomnia, including primary and
secondary insomnia, and factors influencing
insomnia (for example apnoea, personality)
Explanation for other sleep disorders, including
sleepwalking and narcolepsy

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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
Circadian- The Underground Cave Study (Siffre)
Siffre conducted a number of experiments using himself as the sole participant.
He spent 2 months in a cave in the Alps.…read more

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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
pheromones triggered the
change and McClintock
admits that there is a lack of
knowledge about the
chemical reaction taking
place during the experiment.…read more

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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
The Electrooculogram (EOG) - Measures eye movement
The Electromyogram (EMG) - Measures muscle activity in the chin
Research using the EOG has found that is there are 2 types of sleep.…read more

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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 internal clock comes
from experiments in which the SCN was removed from rats and this lead to the
usual rhythm stopping and resulted in the animals not sleeping.…read more

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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 birth. He had a
Circadian rhythm of about 24.9 hours. The lack of light passing through to his
visual pathway meant that it was very difficult for him to regulate his own
personal rhythm.…read more

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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 change
continuously. E.g. 7am-3pm 3pm-11pm & 11pm-7am
Both types of shift work bring on their own set of problems. However it is
possible for non-fluctuating shift workers to adapt a new rhythm.…read more

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DSPS sufferers
are able to get plentiful sleep; it is just delayed compared to normal times.…read more

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