Stages of Sleep Cycle

Stage 1: NREM

Stage lasts a few minutes

lightest level of sleep

Decreased physiological activity begins with gradual fall in VS and metabolism

Sensory stimuli such as noise easily arouses person

Awakened, person feels as though daydreaming has occured

Stage 2: NREM

Stage lasts 10 to 20 minutes

period of sound sleep

relaxation progresses

body functions continue to slow

arousal remains relatively easy

Stage 3: NREM

Stage lasts 15 to 30 min

involves initial stages of deep sleep

muscles are completely relaxed

VS's decline but remain regular

sleeper is difficult to arouse and rarely moves

Stage 4: NREM

Stage lasts approximately 15 to 30 minutes

deepest stage of sleep

if sleep loss has occurred, sleeper spends considerable portion of night in this stage

VS's are significantly lower than during waking hours

sleepwalking and bedwetting sometimes occur

very difficult to arouse sleeper

REM Sleep

Stages usually begins about 90 mins after sleep has begun

duration increases with each sleep cycle and averages 20 minutes

vivid, full-color dreaming occurs; less vivid dreaming occurs in other stages.

Stage is typified by rapidly moving eyes, fluctuating heart and respiratory rates, increased or fluctuating blood pressure, loss of skeletal muscle tone, and increase of gastric secretions.

very difficult to arouse sleeper