Ultradian Rhythm

• Ultradian Rhythms repeat more than once in 24 hrs e.g. the sleep cycle which involves stages of sleep - a cycle of REM/NREM sleep over time. In a night, approx 5 sleep cycles - approx 90 mins each
• In NREM sleep - 4 stages - shallow (stages 1 and 2) into deep or slow-wave sleep (SWS - stages 3 and 4). When you fall asleep, you start in stage 1, move to 2, descending to stage 3 and 4 sleep. The sleeper then starts to moves to stages 3 and 2, then REM sleep. After a period of REM sleep - 90 min cycle - the sleeper descends to stages 3 and 4 again. Known as the sleep staircase - occurs 5 times a night