Sleep notes - Biological Rhythms

Consequences of disrupting bioloigcal rhyms, infradian and circadian rhythms and the disruption of sleep wake cycles

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  • Created on: 12-05-11 11:41
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Psychology Revision ­ Unit 3 Sleep
Biological rhythms (changes in the way biological systems behaviour e.g. sleep wake cycle):
The circadian rhythm:
Key Facts:
Circadian Rhythms last about 24 hours ­ e.g. sleep wake cycle and body temperature.
The Suprachiasmitic Nucleus (SCN) is a small group of cells in the hypothalamus; it lies just
above the optic chasm so it can gain input fairly directly from the eyes.
Morgan removed the SCNs from hamsters and found that their circadian rhythms
disappeared. He also transplanted that SCNs from hamsters who had mutant circadian
rhythms to `normal' hamsters. He found that the hamster receiving the transplant took on the
mutant circadian rhythms.
Silver et al also found that if SCNs are transplanted into an animal who's SCN has been
removed; the animal receiving the transplant have a restored circadian rhythm.
The Sleep wake cycle:
External cues such as knowing which time of day it is do these control our sleep wake cycle?
What happens when our biological clock is freed from external cues do we still know when
we should be awake and asleep?
This study supports other studies by Ashoff and Wever (1976) placed participants in an
underground WW2 bunker with no environmental or social cues. Most people displayed
circadian rhythms of 24-25 hours, however there were some exceptions which were as long
as 29 hours.
Shows that circadian rhythms continue despite isolation from external cues, which
demonstrates the existence of an endogenous clock. ­ However this also shows that
external cues are important as the clock wasn't fully accurate.
Folkard et al (1985): conducted an experiment to see if external cues could be used to
override the internal clock. 12 people lived in a cave for 3 weeks, isolated from all external
cues like natural light. They agreed to go to bed when the clock indicated 11.45pm and
rewake when it indicated 7.45am. At the start the circadian rhythm matched that of the
volunteers, but it quickened, and no longer matched the clock and continued to a 24 hour
cycle rather than the 22 hour cycle set by the experimenter. Suggests that the internal clock
can only be guided by external cues and isn't controlled by it.
After all of the experiments above, the participants only took a few days to resynchronise
their cycles to the available external time cues such as clocks and daylight. (Shows the
impotence of external cues.)

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Research methodology: In all the early studies participants were isolated from variables
which effect there circadian rhythm such as clocks, radio and daylight. However they weren't
isolated from light, as there was an artificial light, which was suggested to not affect the
circadian rhythm, but recent research suggests this isn't true.
Czeisler et al (1999): altered participant's circadian rhythms from 22 to 28 hours just using
dim lighting.…read more

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A02: The biological approach
All studies here propose that behaviour can be explained in terms of structures in the brain
and hormones however human behaviour is often more complex than this. People do also
make choices about what they do which isn't determined by their biology.
Miles et al (1977) a man blind from birth. 24.9 circadian rhythm despite his alarm clocks. Only
way to reset rhythm to 24 hrs was to use sedatives to help him sleep and stimulants to help
him wake.…read more

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Infradian Rhythms (period of more than one day but less than one year):
Monthly Cycles: Driven by fluctuating hormones which regulate ovulation.
Process: pituitary gland releases hormones (FSH ­follicle stimulating hormone and LH ­
luteinising hormone) which stimulate a follicle in one ovary to ripen an egg and trigger the
release of oestrogen. Ripened egg triggers the release of progesterone which causes the
lining of the womb to prepare for pregnancy and increase blood supply.…read more

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Born et al (1999): people who were told to wake up at earlier times of the night than usual had
higher levels of ACTH the stress hormone to help them wake up earlier.
Real world application:
Therapies such as phototherapy uses very strong lights in the evening and/or early morning to
change the levels of melatonin and serotonin. Lights between 6000 or 10,000 which is equivalent to
full daylight.…read more

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Exogenous Zeitgebers:
Resetting the biological clock with exogenous zeitgebers is known as entrainment.
Free-running is where the biological clock operates in the absence of any exogenous cues.
This is the dominant zeitgeber in humans as it can reset the body's main pacemaker, SCN. It
can also reset oscillators located throughout the body because the protein CRY is also light
sensitive (look to the biological clock for further explanation).…read more

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The power of artificial lighting:
Because light is the dominant zeitgeber, will any level of light work as a zeitgeber?
Siffre, Aschoff and Wevers studies of biological rhythms allowed all pps to be exposed to
artificial lighting as they didn't think it would affect circadian rhythms. However Campbell and
Murphy (1996) found that circadian rhythms were shifted by artificial light when subjected to
participant's knees.…read more

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Jet lad: people report less difficulty in adjusting when they fly west ­ phase delay ­ like going
to bed later than usual (E.g. London to new york) then when flying east ­ phase advance ­
like having to get up earlier than usual (New York to London).…read more

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Other factors:
Shift work effects: may not just be due to the disruption of biological rhythms. May be due
to the lack of sleep associated with having to go to bed at unusal times.
Shift workers also experience social disruption as well as disruption to there biological
rhythms. (difficult to meet friends and spend time with family).
Solomon (1993): divorce rates may be as high as 60% amoung all night shift workers.…read more

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Lab experiments: Boivin et al is a lab experiment so although extrenous variables can be
carefully controlled it is hard to tell if this research will apply to everyday life. Therefore field
experiments must also be conducted to confirm the findings.
Boivin and James (2002): conducted this experiment in a field setting with nurses and
confirmed the results. ­ Bright lighting promotes circadian adaptation.…read more


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