AQA A2 Biological Rhythms

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  • Biological Rhythms
    • Circadian Rhythms
      • Last 24 hours. Eg Sleep/Wake Cycle
        • Michel Siffre; Spent 6 months in a cave with no zeitgebers. Pacemakers regulated body however, internal clock extended to 25 hours.
    • Infradian Rhythms
      • Lasts more than 24 hours. Eg, Menstrual Cycle
        • Reinburg found that women's menstrual cycles synchonise to one another due to pheromones which are released into the air
        • Under control of endogenous pacemakers and exogenous zeitgebers
          • Endogenous Pacemakers - hormones, particularly oestrogen and progesterone
          • Exogenous Zeitgebers - women's cycles can synchronise
            • Reinburg found that women's menstrual cycles synchonise to one another due to pheromones which are released into the air
            • Evolutionary advantage - synchronisation meant women would give birth at the same time; this would allow them to share breast feeding
    • Ultradian Rhythms
      • Last less than 24 hours. Eg Sleep Stages
        • Dement and Kleitman found 70% of pps woken during REM sleep reported dreaming
    • Regulated by Internal & External Factors
      • Internal - Endogenous Pacemakers
        • The main one being the SCN - a small group of cells in the hypothalmus located behind the eyes
          • It is sensitive to light & regulates the pineal gland which secretes melatonin
        • Morgan - removed the SCN of hamsters & found the circadian rhythm disappeared
          • Silver - transplanted SCN cells back into the hamsters & found the rhythm re-established
      • External - Exogenous Zeitgebers
        • Light is the main one as it resets the SCN & other oscilators
        • Siffre - no clocks and no natural light --> sleep wake cycle extended to 25 hours
    • Disrupting Biological Rhythms. Eg Shift Work and Jet Lag
      • Genome Lag Theory - our genes have not kept pace with the changes in our environment
      • Shift work involves regular changes to the hours of work. It allows organisations to work around the clock
        • Coren found our average night's sleep is 1.5 hours shorter than 100 years ago
        • Effects
          • Sleep Deprivation - harder to sleep during the day.
            • Tilley & Wilkinson; daytime sleep is 2hrs shorter. REM is affected
          • Depression - disruption of family and social life
            • Solomon; divorce rates are 60% higher in shift workers
          • Effects on health
            • Knuttson et al; individuals that shift work for longer than 15 years were 3 times more likely to develop heart disease
        • Boivin; nightworkers experience a circadian trough when their cortisol levels are lowest between midnight and 4am
      • Jet lag is caused by the body's internal clock being out of step with external cues
        • Phase delay; E-->W. Day is lengthened; have to delay sleep time to adjust (easier)
        • Phase advnace; W-->E. Day is shortened; have to advnace body clock to catch up (harder)
        • Effects
          • Performance Decrement
            • Recht, Lew & Schwartz; US baseball teams over 3 year period. Found teams traveling E-W before a game won 44% of games, those traveling W-E won only 37%
          • Long Term Health Effects - Women
            • Female flight attendants often find their menstrual cycles stop & can find it increasingly difficult to get pregnant
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