What can cause this clock to become out of balance?
Major alternations in sleep (jet lag, shift work)
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Example of free running circadian clock?
Micheal Siffre
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What did he do?
Spent long times underground isolated from external cues (e..g light)
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Effects?
Circadian rhythm stretched out to as long as 48 hours
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Other circadian rhythms? (2)
1) Core body temp 2) Hormone production
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Low/high point for core body temp?
36 around 4:30 am / 38 around 6pm
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When is there a slight drop - what might this help explain?
2-4 pm - post lunch sleepiness?
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Hormone that follows a sleep wake cycle?
Melatonin
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What is this secreted from?
Pineal gland
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When does it increase/decrease
in darkness to promote sleepiness / in morning to promote wakefulness
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(+)
4 Brit pps in Antarctic station - after 3 months of being in continuous darkness - cortisol peaked at noon (not at wake)
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Real world
Chronotherapeutic meds - ensure right conc. is released at the right time (e.g. greater risk of hearth attack in morning, take at night & released in morning)
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Methodology
Assumed that pps isolated from all variables - but recently found that circadian can be altered with artificial light
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Genetic
Have 'morning' and 'evening' people / circadians can range from 13-65 hours
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