The sleep staircase Sleep does not progress through these stages in sequence. (1 2 3 4 – 1 2 3 4) Sleep begins in stage 1 and goes into stages 2, 3 & 4.

The sleep staircase After stage 4 sleep, stage 3 & then stage 2 sleep are repeated before entering REM sleep. (1 2 3 4 3 2 REM – 2 3 4 3 2 REM) Once REM sleep is over, we usually return to stage 2 sleep. We go through these sleep cycles four or five times a night.

REM gets longer On average, we enter the REM stage about 90 minutes after falling asleep. The 1st REM cycle might last a short amount of time, but each cycle becomes longer. So we dream more toward morning.

Normal Sleep Architecture Entered through NREM Approximately 90 minute cycle including NREM and REM Slow wave dominates first third of night REM sleep dominates last third of night REM sleep: 20-25% total sleep time

Clips Stages of sleep http://youtu.be/qEWbu37fH9k Sleep cycles (8 mins 46) http://youtu.be/9VCIY-UvcII

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