Normal Sleep Architecture Joseph R. Deatherage, R. David Roden, and Kenneth Zouhary Normal sleep is a complex and critical physiological activity. It is characterized by discrete neurological patterns that represent different stages of sleep. To have restful sleep, each phase of sleep must be completed; otherwise, sleep disruption will result. Disruption of sleep architecture will result in excessive daytime somnolence and can lead to systemic disease. (Semin Orthod 2009;15:86-87.) Š 2009 Elsevier Inc. All rights reserved.
ormal sleep architecture is characterized by two forms. These forms are referred to as non-rapid eye movement (NREM) and rapid eye movement (REM). These sleep states alternate throughout the sleep cycle. Each of these sleep states is associated with specific electroencephalogram (EEG) patterns, altered skeletal muscle tone, altered psychological activity, and respiratory patterns.1 Sleep is initiated in stage 1 NREM and progressively moves through deeper stages 2, 3, and 4 before reaching REM sleep. During these stages of NREM sleep, specific patterns of EEG activity occur. REM sleep occurs some 100 minutes later after sleep initiation. As the sleep episode progresses, REM and NREM sleep cycles alternate approximately every 90 minutes. REM sleep is associated with vivid dreaming and diminished tone of the skeletal muscles of the airway and limbs. NREM sleep is associated with synchronous EEG complexes. As humans age, there are changes in sleep architecture and patterns. However, after puberty REM sleep occupies 20% to 25% of total sleep throughout life and continues alternating with NREM except in dementia. Sleep architecture can be altered by previous sleep-wake history, environmental alterations, medications, alcohol consumption, and sleep disorders.
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Department of Oral and Maxillofacial Surgery, University of Alabama School of Dentistry, Birmingham, AL. Address correspondence to Joseph R. Deatherage, DMD, MD, Department of Oral and Maxillofacial Surgery, University of Alabama School of Dentistry, 1919 7th Avenue South, Birmingham AL 35294. E-mail: jddmdmd@uab.edu Š 2009 Elsevier Inc. All rights reserved. 1073-8746/09/1502-0$30.00/0 doi:10.1053/j.sodo.2009.01.002
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The sleep process normally begins with NREM sleep. In disease states such as narcolepsy sleep can begin with REM sleep. Early sleep also is associated with decreased muscle tone, which affects the limbs and support of the airway. As the process of sleep continues, there are slow asynchronous eye movements. Stage 1 sleep is the beginning of sleep onset. At this stage sleep is easily disrupted. In sleepdeprived individuals stage 1 sleep increases as a percentage of total sleep. Stage 2 sleep is characterized by specific EEG complexes. It is more difficult to be awakened by external stimuli at this stage of sleep. Sleep continues through NREM stages 3 and 4. This is referred to as deep sleep, or delta sleep, because of specific EEG patterns. REM sleep occurs through the sleep cycle, alternating with NREM periods. The REM cycles become progressively longer. It is believed that this distribution of REM sleep towards the end of the sleep cycle represents a circadian pattern. It also associated with alterations in body temperature. Most adults in the absence of disease conditions or other abnormal environmental intrusions sleep between 7.5 and 8.5 hours per sleep cycle. This amount is highly variable and defies easy attempts to quantify what is normal. There exist age-related changes in sleep architecture. Nonetheless, the amount of REM sleep remains constant in the absence of pathology for all ages after puberty. Arousal from sleep increases with age. These arousals can be the result of many factor, including respiratory disturbances. Ingestion of drugs or alcohol has an effect on sleep architecture. Alcohol consumption
Seminars in Orthodontics, Vol 15, No 2 (June), 2009: pp 86-87
Normal Sleep Architecture
before sleep increases the deep sleep period, NREM stages 3 and 4, but suppresses REM sleep early in the sleep cycle. Later as the alcohol is metabolized there can be REM sleep rebound. In summary, sleep is a critical physiological activity that affects all aspects of an individual’s existence. Sleep is associated with specific neurological events that can be quantified in the
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sleep laboratory with the polysomnogram. Incomplete or fragmented sleep can negatively impact the quality of life and result in systemic disease.
Reference 1. Kryger M, Roth T, Dement W: Principles and Practice of Sleep Medicine, 4th edition, 2005