Why do we need sleep?

  • sleep takes up almost 1/3 of our livesThe-Sleep-Cycle-1
  • when deprived of it, we feel terrible and our performance suffers
  • researchers, however, are not sure exactly why we need sleep – just that we do

What are the effects of lack of sleep?

  • Major effects
    • fatigue
    • diminished immunity to disease
    • slight hand tremor
    • irritability
    • inattention
    • when performing monotonous activities, results can be devastating (i.e. driving)
    • on short, highly motivating tasks there is little effect
  • lack of sleep affects everyone differently

The Categories of Sleep

  • There are two major categories of sleep: NREM and REM sleep
  • REM Sleep (Rapid Eye Movement)
    • makes up 20 – 25% of a normal nights sleep
    • a sleeper will experience:
      • rapid eye movements
      • a rush of Epinephrine (adrenaline)
      • blood pressure rises
      • heart rate and respiration become faster and irregular
      • brain temperature increases
      • large muscles of the body become paralyzed
      • vivid dreams
  • NREM Sleep (Non-Rapid Eye Movement)
    • makes up 75 – 80% of a normal nights sleep
    • there are four stages of NREM sleep
    • a sleeper will experience:
      • no rapid eye movements
      • heart rate and respiration that is slow and regular
      • little body movement
      • blood pressure and brain activity are at their lowest points of the 24-hour period

The Stages of NREM Sleep

  • sleep follows a fairly predictable pattern every night – we sleep in cyclesNREM-sleep-stages
    • each cycle lasts approximately 90 minutes, and consists of one or more stages of NREM sleep, which is then followed by a period of REM sleep
  • The stages of NREM sleep:
    • Stage One:
      • a few minutes long
      • very light sleep
      • the transition between waking and sleeping
      • Stage Two:
        • 50% of a night’s sleep
        • a somewhat deeper sleep
        • sleeper is harder to awaken
      • Stage Three:
        • a few minutes long
        • the beginning of slow-wave sleep (aka. deep sleep)
        • sleep gradually becomes deeper and deeper
        • growth hormone is secreted
      • Stage Four:
        • approximately 40 minutes long
        • slow-wave sleep – the deepest sleep
        • sleeper is the hardest to awaken
        • growth hormone is secretedThe-Sleep-Cycle

The Complete Sleep Cycle (1, 2, 3, 4, 3, 2, REM)

  • NREM sleep descends from stage 1 to stage 4
  • goes back to stages 3 and 2
  • Enters the first REM period of the night (REM lasts 10 – 15 minutes)
    • at the end of this REM cycle, the first sleep cycle is complete
  • sleep goes from the REM period to stage 2 sleep, and follows the same cycle as before
  • after 2 cycles (approx. 3 hours), sleepers will usually get no more stage 4 sleep and the REM period gets longer
  • most people sleep about 5 sleep cycles (7.5 – 8 hours) per night
  • results in 1.5 hours of slow-wave sleep and 1.5 hours of REM sleep


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