Biological rhythms: Endogenous pacemakers and exogenous zeitgebers

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What are endogenous pacemakers?
An internal body clock which regulates biological rhythms, eg. the suprachiasmatic nucleas (SCN)
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What are exogenous zeitgebers?
External cues affecting our biological rhythms, eg. light and dark
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What's the suprachiasmatic nucleus [SCN] ?
A bundle of nerve cells in the hypothalamus in each hemisphere in the brain. It's the primary endogenous pacemaker in maintaining circadian rhythms, eg. sleep/wake system.
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WHat's the pineal gland?
A pea like structure just behind the hypothalamus. It receives information from the SCN about light and regulates melatonin production accordingly.
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What's melatonin?
A chemical that induces sleep.
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How does light and dark cause melatonin the be released?
Changes in light are picked up by receptors in the eye, communicating this to the SCN. This info is then passed on to the pineal gland, which, depending if it's light or dark, will release melatonin accordingly
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Research into the SCN - What did DeCoursey et al do?
Destroyed the SCN in 30 Chipmunks and returned them to their natural habitats. Observed them for 80 days and found a significant proportion and been killed by predators, presumably because they had been awake and predators could hear and find them
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Research into the SCN - What did Ralph et al do?
Bred mutant hamsters with 20 hour sleep/wake cycles. Transplanted SCN cells into brains of normal hamsters. These hamsters cycles also now became 20 hours.
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Research - light - Campbell and Murphy, what did they do?
Light can be detected even through skin receptor sites. 15 ps were woken at various times and had light shone on the backs of their knees. Manages to change their sleep/wake cycles by up to 3 hours in some cases. Light=powerful zeitgeiber
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Research - social cues
Babies sleep/wake cycles are random at first. @ 6 weeks, circadian rhythms begin. @ 16 weeks, most babies are entrained. Key influence = parents imposing a schedule - bedtimes & meal times
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Evaluation - Beyond the master clock
Perhaps SCN isn't the main indogenous pacemaker & other pacemakers may be just as important that work individually, eg. Ralph
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Evaluation - Ethics in animal studies
Problems in generalising findings from animals to humans. & Unethical, eg. Decoursey's experiment resulted in the death of Chipminks
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Evaluation - Influence of exogenous zeitgabers may be overstated
Artic - Summer = always light. Winter = always dark, yet people still continue their sleep/wake cycle. Man with a longer cycle (24.9) had to use sedatives to sleep.
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Evaluation - Methodological issues in studies
Campbell & Murphy - lack of control - extraneous light - poor methodology
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Evaluation - Interactionist system
Pointless studies - we will always have light so why does it matter? indogenous&endogenous work together.
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Other cards in this set

Card 2

Front

What are exogenous zeitgebers?

Back

External cues affecting our biological rhythms, eg. light and dark

Card 3

Front

What's the suprachiasmatic nucleus [SCN] ?

Back

Preview of the front of card 3

Card 4

Front

WHat's the pineal gland?

Back

Preview of the front of card 4

Card 5

Front

What's melatonin?

Back

Preview of the front of card 5
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