STAGES OF THE SLEEP CYCLE

Stage 1 NREM

Includes lightest level of sleep.

Stage lasts a few minutes.

Decreased physiological activity begins whit grandual fall in vital signs and metabolism.

Sensory stimuli such as noise easily arouses person.

Awakened, person feels as though daydreaming has occurred.

Stage 2 NREM

Period of sound sleep.

Relaxation progresses.

Arousal remains relatively easy.

Stage lasts 10 to 20 minutes.

Body functions continue to slow.

Stage 3 NREM

Involves initial stages of deep sleep.

Sleeper is difficult to arouse and rarely moves.

Muscles are completely relaxed.

Vital signs decline but remain regular.

Stage lasts 15 to 30 minutes.

Stage 4 NREM

Deepest stage of sleep.

Very difficult to arouse sleeper.

If sleep loss has occurred, sleeper will spend considerable portion of night in the stage.

Vital signs are significantly lower than during waking hours.

Stage lasts approximately 15 to 30 minutes.

Sleepwalking and enuresis (bad-wetting) sometimes occur.

REM Sleep

Vivid, full-color dreaming occurs.

Less vivid dreaming occurs in other stages.

Stage usually begins aboud 90 minutes after sleep has begun.

Typified by autonomic response of rapidly moving eyes, fluctuating heart and respiratory rates, and increased or fluctuating blood pressure.

Loss of skeletal muscle tone occurs.

Gastric secretions increase.

Very difficult to arouse sleeper.

Duration of REM sleep increases whit each cycle and averages 20 minutes.