sleep cycle and sleep stages


  • sleep cycle composes of different sleep stages
  • normally person goes through 4-6 cycles
  • cycle takes about 90-120 minutes

Stages

Awake

  • alpha waves: relaxed
  • beta waves: active concentration

N1

  • first fall asleep
  • short
  • body not fully relaxed
  • brain and body starts to slow
  • easy to wake
  • as night goes on, sleeper spends less time in stage 1
  • theta waves

N2

  • more relaxed, slower breath, slower heart rate
  • eye movement stops
  • brain activity slows
  • short bursts of activity: helps wake up by external stimuli
  • becomes longer as the night goes
  • half of time in spent in N2
  • teeth grinding (bruxism)
  • K complex and sleep spindles

N3

  • deep sleep
  • harder to wake up
  • even more relaxed
  • delta waves or slow wave sleep (SWS)
  • maybe critical for body recovery, growth, immune system
  • more time in deep sleep earlier, then more time in REM later
  • sleep walking and enuresis

REM

  • brain activity higher
  • paralysis of muscle, penile/clitoral erections
  • increased pulse, blood pressure
  • eyes move quickly
  • essential for cognitive functions
  • vivid dreams
  • 10-40 min for every 90 min sleep
  • REM rebound: body compensates with poor sleep by having higher REM sleep during next period
  • sawtooth waves

Normal Changes

  • older = less time in REM

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Footnotes

  1. https://www.sleepfoundation.org/how-sleep-works/sleep-latency