Stages of Sleep

Abstract

• NREM Sleep – Nonrapid eye movement; non-REM o Stage 0: Awake; alpha rhythm o Stage 1: Transition from wakefulness to sleep; light sleep o Stage 2: Transition between delta and REM sleep; medium sleep; sleep spindles and K complexes • Delta Sleep – non-REM o Slow-wave sleep o Stage 3: Deeper depth of sleep than stage 2; approximately 20% to 50% of a period consists of delta waves o Stage 4: Greater delta-wave activity than stage 3; very deep sleep; greater than 50% of a period consists of delta waves • REM Sleep – Rapid eye movement o Active EEG o Dream sleep o Depth of sleep between stage 2 and stage 3 o Loss of muscle tone except ocular and respiratory muscles o REM sleep occurs 60 to 90 minutes after onset of sleep • Polysomnography is used to determine sleep states and includes electroencephalograms (EEGs), electromyograms (EMGs), electrocardiograms (ECGs), and eye movements. • Normal sleep progresses through the four stages of non-REM sleep in order 1 through 4. Stage 2 then occurs as a transition between delta sleep and REM sleep. REM sleep occurs next, and the entire cycle lasts about 90 minutes. Four to six cycles occur each night in a normal adult. 106 15. Sleep and Sleep Disorders