Biological Rhythms & Sleep

Biological Rhythms

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Biological Rhythms

Circadian- 24 hour-cycle, e.g the 24 hour sleep-wake cycle

Ultradian- A regular pattern with a cycle of less than 24 hours, e.g, the NREM/REM sleep cycles in a nights sleep

Infradian- A regular, repeating pattern with a cycle that is longer than 24hours, e.g, the human monthly menstrual cycle


Most obvious -sleep wake cycle. In any 24hour period we go to sleep and wake up.

Another-temperature in humans varies over 24hour day, reaching peak in late afternoon and a low point in early morning.

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Biological Rhythms- Circadian rhythms

Research Findings

Meddis- average of 7-8 hours sleep per 24 hours

Michael Siffre- demonstration of innate circadian rhythm. In other words the sleep wake cycle is something that we are born with and is biologicaly determined.

He volunteered live underground in caves where there was: no daylight or any other clues about what time it was e.g. clocks & tv. Monitored and found that he settled into a regular cycle of sleeping and waking. (24.9 hour rhythm) Each day he was waking up nearly an hour later. Effect was by the end of his months he had "lost" a considerable number of days and thought he had been underground for less time than actually passed.

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Biological Rhythms- Circadian rhythms


Criticism of siffre study- it involved only one individual. Cannot generalise these findings to other human beings.

However results have been confirmed by other cave studies.e.g. Kleitman & the study that looked at a blind individual.

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Great, thanks a lot :)

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