Infradian and Ultradian Rhythms

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Ultradian Rhythms

  • Sleep Stages
  • Daily cycles of wakefulness and sleep follow a circadian rhythm, within the sleep portion, a cycle called an ultradian rhythm exists.
  • These are the five stages of sleep; the first four are called NREM sleep and the last is REM.
  • One sleep cycle goes through all 5 stages and lasts 90 minutes.
  • Stages 1 and 2 are light sleep; characterised by a change in the electrical activity of the brain.
  • The awake brain produces a pattern called a beta wave. 
  • As you are more relaxed the brain waves become slower and more regular and have a greater amplitude. This is an alpha wave.
  • As you go to sleep they slow down further which is a theta wave.
  • Stages 3 and 4 are characterised by even slower delta waves. These are called SWS.
  • In SWS, most of the bodys physiological repair work happens and biochemical processes take place such as production of growth hormones.
  • Each sleep cycle is about 60 minutes in early infancy, increasing to 90 minutes during adolescence.
  • Basic Rest-Activity Cycle
  • The 90 minute cycle is located within a 24 hour circadian cycle, would make sense to find this 90 minute clock was ticking throughout the day.
  • It is called the basic rest activity cycle.
  • Eating and drinking behaviour in a group of psychiatric patients over 6 hours was observed.

Infradian Rhythms

  • Monthly Cycles
  • Female menstrual cycle is an obvious infradian rhyth,s
  • Fucntion of the menstrual cycle is to regulate ovulation.
  • Pituitary gland releases FSH


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