Outline and Evaluate an Ultradian Rhythm

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Outline and evaluate one or more biological rhythms (12 marks 4+8) An Ultradian rhythm is a biological rhythm that spans less than 24 hours such as the basic rest- activity cycles or the stages of sleep. Sleep consists of five stages and one cycle through these stages lasts for about 90 minutes. The first four stages are known as NREM sleep (non-rapid eye movements) and the fifth stage is called REM sleep (rapid eye movement) Stage one and two are characterised by a relaxed state. EEG shows alpha and theta brain waves during these stages and heart rate slows and temperature drops. Stage 3 and 4 also known as slow wave sleep (SWS) is characterised by delta brain waves, during these stages most of the body’s repair work is undertaken. In REM sleep there is fast, desynchronised EEG resembling the awake brain and the body is paralysed (cataplexy). Dement and Kleitman’s (1957) carried out a lab study with 9 participants and showed that when patients were woken during REM sleep they were far more likely to report dreaming. As the night progresses SWS gets shorter and REM sleep longer. Dement and Kleitman can be criticised for their very small sample size as it is unlikely to represent the range of individual differences in sleeping and dreaming. Factors such as drugs, stress and obesity all affect the quality and length of sleep and so the stages of sleep. Dement et al’s small sample is not sufficient to inform our understanding of the wider population and their ultradian rhythm. However, they have used reliable methods for investigating sleep as EEGs represent a standardised test which can be repeated and the results checked for consistency. A further criticism is their use of a sleep lab which, while providing a high degree of control does take participants away from their natural sleep setting and makes the act unlike sleeping at home which present an issue for

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