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Biological Rhythms: The Circadian Rhythm
Rhythms that last about 24 hours. the two bestknown circadian rhythms are the sleepwake cycle and the
body temperature cycle.
SleepWake Cycle
Endogenous pacemakers
The sleepwake cycle is controlled by an endogenous pacemakers (internal body clock). It tells our body
when to feel sleepy and…

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Ultradian and Infradian Rhythms
Ultradian Rhythms
The sleep staircase
There are 5 stages of sleep. The first 4 are NREM and the fifth is REM.
1) Light, 45% of total, occasional muscle twitching. Muscle activity slows, Alpha waves.
2) 4555% of total, Theta waves, greater amplitude, sleep spindles.
3) 46%…

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(+) Can be controlled by exogenous cues: (Russell et al., 1980) when sweat from one group of women was
rubbed on the upper lip of the second group, their menstrual cycles synchronised with their individual donor.
Suggesting synchronisation of menstrual cycles can be effected by pheromones.

Reallife application: Consequences of…

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their SCN's disconnected were compared to 2 other groups of chipmunks 24 surgical controls and 20 intact
controls. 80 days later signiicantly more of the SCNlesioned chipmunks had been killed by weasels.
Presumably because they remained awake in their burrows and the weasels could here them.

Research into the…

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Disrupting Biorhythms
Shift Work
Decreased alertness
(Boivin et al., 1996) Nightworkers often experience a circadian 'trough' of decreased alertness during their
shifts. This occurs between midnight and 4am when CBT is lowest.
Sleep deprivation is another explanation for decreased alertness. Shift workers often experience sleep
deprivation because when they finish…

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Reallife application: melatonin is a natural hormone that induces sleep and has been put forward as a
'miracle' cure.
(Herxheimer and Petrie, 2001) where melatonin was taken near bedtime it was remarkably effective.
Reallife application: social customs can help entrain biological rhythms i.e. when travelling it helps to eat

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Individuals sleep for an average of 910 hours per night. The amount of REM sleep is less than in childhood.
Circadian rhythms also change so that teenagers feel more awake later at night and have more difficulty getting
up early (a delayed sleep phase).

(+) Hormones are generally released…

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Case studies: The study of sleep deprivation is generally restricted to case studies. The main problem
therefore is that the participants are likely to be unique. I.e. someone who has difficulty sleeping is less likely
to volunteer for studies, and people who do volunteer are probably highly motivated to try…

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Warmblooded animals use energy to maintain temperature. This is especially true for small animals with a
high metabolic rate.

(+) (Zepelin and Rechtschaffen, 1974) smaller animals, with a higher metabolic rate slept more than larger
() (Capellini et al., 2008) there was a negative correlation between metabolic rate and…

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Explanations of Insomnia
May involve trouble falling asleep (initial), trouble remaining asleep (middle), or waking up too early (terminal).
It is transient, intermittent, or chronic.
Primary insomnia
Where insomnia simply occurs on its own, for more than a month.
It is the persons primary problem.
It may be that they…


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