Section 6. Brain, Spinal Cord, and Nerve Disorders

Chapter 81. Sleep Disorders

Topics: Introduction | Insomnia | Hypersomnia | Narcolepsy | Sleep Apnea Syndromes | Parasomnias | Sleep Disorders in People With Dementia

Introduction

Sleep disorders are disturbances that affect the ability to fall asleep, stay asleep, or stay awake or that produce abnormal behaviors during sleep, such as night terrors or sleepwalking.

Sleep is necessary for survival and good health, but why sleep is needed and exactly how it benefits people are not fully understood. Individual requirements for sleep vary widely; healthy adults may need as few as 4 hours or as many as 10 hours of sleep every day. Most people sleep at night. However, many people must sleep during the day to accommodate work schedules--a situation that often leads to sleep disorders.

How long a person sleeps and how rested a person feels after waking can be influenced by many factors, including level of excitement or emotional distress, age, diet, and use of drugs. For example, some drugs make a person sleepy, and others make sleeping difficult. Some food components or additives, such as caffeine, strong spices, and monosodium glutamate (MSG), may affect sleep. Older people tend to fall asleep earlier, to awaken earlier, and to be less tolerant of changes in sleep patterns (for example, they may be more prone to jet lag). Compared with younger adults and children, older people are more easily aroused from sleep and awaken more often during the night. Whether older people need less sleep is unclear. Napping during the day may help compensate for poor sleep during the night, but it may also contribute to the problem.

All sleep is not the same. There are two main types of sleep: rapid eye movement (REM) sleep and nonrapid eye movement (non-REM) sleep, which has four stages. People normally cycle through the four stages of non-REM sleep, usually followed by a brief interval of REM sleep, 5 or 6 times every night.

Sleep progresses from stage 1 (the lightest level, during which the sleeper can be awakened easily) to stage 4 (the deepest level, during which the sleeper can be awakened only with difficulty). In stage 4, blood pressure is at its lowest, and heart and breathing rates are at their slowest.

During REM sleep, electrical activity in the brain is unusually high, somewhat resembling that during wakefulness. The eyes move rapidly, and muscles may jerk involuntarily. The rate and depth of breathing increase, but the muscles, except for the diaphragm, are greatly relaxed--more so than during the deepest levels of non-REM sleep.

Most dreaming occurs during REM sleep. Most talking during sleep, night terrors, and sleepwalking occur during stages 3 and 4.

See the figure Stages of the Sleep Cycle.

Usually, sleep disorders can be diagnosed based on the medical history, including a description of the current problem, and the results of a physical examination. When the diagnosis is uncertain, doctors may recommend evaluation in a sleep laboratory. The evaluation consists of polysomnography and observation of unusual movements during an entire night's sleep. Polysomnography includes recording and monitoring of breathing, heart rate, and other functions; electroencephalography (EEG), which records the brain's electrical activity (see Section 6, Chapter 77); and electro-oculography, which records eye movement during REM sleep.

See the sidebar Science Wakes Up to Sleep Disorders.