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Biological Rhythms Notes

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Biological rhythms

A cyclical variation over some period of time in physiological and psychological processes - frequencies of rhythms differ.

Types of rhythms:


Circadian - consistent cyclical variations that occur over 24 hours Ultradian - shorter than one day - more than one cycle every 24 hours Infradian - longer than one day - rhythms occur less than every 24 hours

Examples of circadian rhythms:


Sleep-wake cycle Heart rate, metabolic rate, breathing rate and body temperature all have maximum values in late afternoon and minimum values in early morning Hormone concentrations also vary in the body over the course of the day e.g. in women prolactin, a hormone that stimulates milk production, peaks at night Opening and closing of heliotropic plants Although circadian rhythms tend to be synchronised with cycles of light and dark, other factors e.g. ambient temperature, meal times, stress and exercise can influence timing as well

Examples of infradian rhythms:


Hibernation in squirrels Human menstrual cycle Migration of birds

Examples of ultradian rhythms:

Stages of sleep cycle

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