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Describe and evaluate research on ultradian and infradian rhythms

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´╗┐Describe and evaluate research on ultradian and infradian rhythms ( 9+ 16 Marks) Ultradian rhythms are bodily rhythms that occur more than once in a 24 hour period, for example the different stages of sleep. Stages 1 and 2 are characterized by alpha and theta waves (electrical activity of the brain). In this period of sleep we are in a relaxed state and are easily woken. Heart rate slows and core body temperature drops. Next is stages 3 and 4 (slow wave sleep) where the body is in ?repair mode? because of the production and secretion of growth hormone which enables protein synthesis. This stage is defined by delta wave brain activity. REM (Rapid Eye Movement) is the final sleep stage, called ?paradoxical sleep? because the body is paralysed but brain activity resembles that of an awoken person. The whole cycle lasts for 90 minutes and each cycle is repeated 4 or 5 times a night. ...read more.


The menstrual cycle spans over a period of 28 days. The cycle starts with the ripening of an egg and the thickening of the lining of the womb. Various hormones maintain the lining with the cycle ending with the shedding of this lining. The release of these hormones are co-ordinated by the pineal gland which is speculated to be influence by light levels and the secretion of melatonin. McClintock conducted a case study (long span of 10 years) than involved 29 women who had a history of irregular, spontaneous ovulation. They wore cotton pads under their arms (to transfer sweat to it) which they were told to wear for 8 hours. They were also instructed to bathe with unperfumed products so it wouldn?t interrupt the study of their sweat and the pheromones which it contains. Then the sweat pads were treated with alcohol and frozen. These pads were then wiped under the noses of the other women on a daily basis. ...read more.


Another example of an infradian rhythm is Seasonal Affective Disorder (SAD). It is common for people to experience ?winter blues? but people with SAD have a more severe form of this, showing symptoms of chronic depression through the darker months. This may be due to an increase in the production and secretion of melatonin which happens in the dark. The longer time spent in the dark, the greater levels of serotonin and melatonin secreted. The main criticism of this explanation of SAD is that it focuses primarily on it being a natural outcome of infradian rhythms, but alternatively it could be the consequence of a disrupted circadian rhythm. In the UK, as the seasons change from summer to winter, the circadian rhythm may be thrown out of phase. People continue to get up at about the same time but often go to sleep earlier because it is darker earlier. This means that the biological system gets the impression that time is shifting and the result is similar to jet lag, which may explain why explain why the symptoms of SAD are similar to those of jet lag. ...read more.

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