Infradian and Ultradian Rhythms

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  • Infradian and Ultradian Rhythms
    • UItradian
      • Sleep stages
        • Within sleep there are sleep stages with the first four being NREM sleep and the fifth stage being REM.
        • One cycle goes through all of the stages and lasts about 90 minutes.
        • Stages 1 & 2 are light sleep and are characterised by a change in the electrical activity of the brain.
          • The awake brain produces beta waves then as you become more relaxed the waves become slower and more regular so have greater amplitude which is an alpha wave. As you go to sleep the waves slow down even further and become theta waves with more frequency and greater amplitude.
        • Stages three and four are characterised by even slower delta waves. These stages are called slow-wave sleep.
          • In slow-wave sleep most of the body's "repair work" takes place an d growth hormone is also produced.
        • These cycles continue throughout the night and the slow-wave sleep period gets shorter and REM periods get longer.
        • There is an issue with studies on REM sleep.
          • The issue is that there is an assumption that REM sleep is dreaming sleep. Dement and Kleitman woke participants up at the times when their brain waves were characterised by REM sleep. They found that participants were highly likely to report dreaming. However, they also found that participants would dream out of REM sleep and others would not dream with in REM sleep.
            • This means that we cannot assume that REM sleep is dreaming sleep. However, Dement and Kleitman's research may provide theorists with a way to explain dreaming.
    • Infradian
      • Monthly cycles
        • The pituitary gland releases hormones which stimulates a follicle in one ovary to ripen an egg and triggers the release of oestrogen.
        • Once the egg has ripened progesterone is secreted and the lining of the womb prepares for pregnancy by increasing its blood supply.
        • About two weeks after ovulation, if there is no pregnancy, progesterone is reduced and the lining of the womb sheds.
        • The menstrual cycle can also be controlled by exogenous cues.
          • Research has shown that when several women live together and do not take any oral contraceptive, the tend to menstruate at the same time every month. One study, daily samples of sweat were collected from one group and rubbed onto the upper lip of a second group. The groups were kept separate but the cycles synchronised.
            • This suggests that the synchronisation of menstrual cycles can be controlled by pheromones.
      • Season affective disorder
        • A depressive condition
        • Individuals become depressed during the winter months but get better during the summer months.
        • Research studies have found that melatonin and serotonin are secreted when it's dark. the more dark the more of these hormones.
        • Seasonal affective disorder could be a consequence of a disrupted circadian rhythm.
          • As the seasons change the circadian rhythm may be thrown out of phase. People continue to get up at the same time but go to bed earlier because it's darker.
            • The biological system then gets the impression that time is shifting and seasonal affective disorder is then caused. This shows that it may be a consequence of the disturbance of a circadian rhythm

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