TAILIEUCHUNG - Chapter 028. Sleep Disorders

Physiology of Sleep and Wakefulness Most adults sleep 7–8 h per night, although the timing, duration, and internal structure of sleep vary among healthy individuals and as a function of age. At the extremes, infants and the elderly have frequent interruptions of sleep. In the United States, adults of intermediate age tend to have one consolidated sleep episode per day, although in some cultures sleep may be divided into a midafternoon nap and a shortened night sleep. Two principal systems govern the sleep-wake cycle: one actively generates sleep and sleep-related processes and another times sleep within the 24-h day. . | Chapter 028. Sleep Disorders Physiology of Sleep and Wakefulness Most adults sleep 7-8 h per night although the timing duration and internal structure of sleep vary among healthy individuals and as a function of age. At the extremes infants and the elderly have frequent interruptions of sleep. In the United States adults of intermediate age tend to have one consolidated sleep episode per day although in some cultures sleep may be divided into a midafternoon nap and a shortened night sleep. Two principal systems govern the sleep-wake cycle one actively generates sleep and sleep-related processes and another times sleep within the 24-h day. Either intrinsic abnormalities in these systems or extrinsic disturbances environmental drug- or illness-related can lead to sleep or circadian rhythm disorders. States and Stages of Sleep States and stages of human sleep are defined on the basis of characteristic patterns in the electroencephalogram EEG the electrooculogram EOG a measure of eye-movement activity and the surface electromyogram EMG measured on the chin and neck. The continuous recording of this array of electrophysiologic parameters to define sleep and wakefulness is termedpolysomnography. Polysomnographic profiles define two states of sleep 1 rapid-eye-movement REM sleep and 2 non-rapid-eye-movement NREM sleep. NREM sleep is further subdivided into four stages characterized by increasing arousal threshold and slowing of the cortical EEG. REM sleep is characterized by a low-amplitude mixed-frequency EEG similar to that of NREM stage 1 sleep. The EOG shows bursts of REM similar to those seen during eyes-open wakefulness. Chin EMG activity is absent reflecting the brainstem-mediated muscle atonia that is characteristic of that state. Organization of Human Sleep Normal nocturnal sleep in adults displays a consistent organization from night to night Fig. 28-1 . After sleep onset sleep usually progresses through NREM stages 1-4 within 45-60 min. Slow-wave sleep NREM .

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