Sleep Stages

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Stages of Sleep

  • Daily cycles of wakefulness and sleep follow a circadian rhythm
  • Within the sleep portion = ultradian rhythm
  • First four stages = NREM sleep
  • Fifth stage = REM sleep
  • Accompanying movements of the eye beneath of closed lids
  • One sleep cycle goes through all five stages and lasts about 90 minutes
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Stages 1 and 2

  • Light sleep
  • Change in the electrical activity of the brain
  • Awake brain = beta waves 
  • More relaxed = alpha waves
  • Brain waves become slower and more regular, and have a greater amplitude
  • Going to sleep = theta waves 
  • Accompanied by bursts of activity 
  • Incrased wave frequency = sleep spindles 
  • Increase wave amplitude = K complexes
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Stages 3, 4 and 5

  • Stages 3 and 4
  • Characterised by even slower delta waves
  • Slow Wave Sleep (SWS)
  • Very hard to wake someone up 
  • Person is not unconscious and will be aroused by, for example, a baby crying
  • 'Repair work' is undertakn 
  • Important biochemical processes take place such as production of growth hormones

Stage 5:

  • REM sleep
  • Fast, desynchronised EEG activity resembling the awake brain
  • These cycles continue hroughout the night
  • SWS period gets shorter
  • REM gets slightly longer as the night continues 
  • Each sleep cycle = 90 minutes 
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