Sleep disorders

The most common sleep disorder, and the one most people are familiar with, is insomnia. Some people have difficulty falling asleep initially, but other people fall asleep, and then awaken part way through the night, and cannot fall asleep again. Although there are a variety of short-acting sedatives and sedating antidepressant drugs available to help, none of these produces a truly natural and restful sleep state because they tend to suppress the deeper stages of slow wave sleep.

Excessive daytime sleepiness may have many causes. The most common are disorders that disrupt sleep and result in inadequate amounts of sleep, particularly the deeper stages. These are usually diagnosed in the sleep laboratory. Here, the EEG, eye movements and muscle tone are monitored electrically as the individual sleeps. In addition, the heart, breathing, and oxygen content of the blood can be monitored.

Obstructive sleep apnea causes the airway muscles in the throat to collapse as sleep deepens. This prevents breathing, which causes arousal, and prevents the sufferer from entering the deeper stages of slow wave sleep. This condition can also cause high blood pressure and may increase the risk of heart attack. There is also an increased risk of daytime accident, especially automobile accidents, which may prevent driving. Treatment is complex and may include a variety of attempts to reduce airway collapse during sleep. While simple things like losing weight, avoiding alcohol and sedating drugs prior to sleep, and avoiding sleeping on one’s back can sometimes help, most people with sleep apnea require positive airway pressure to keep the airway open. This can be provided by fitting a small mask over the nose that provides an air stream under pressure during sleep. In some cases, surgery is needed to correct the airway anatomy.

Periodic limb movements of sleep are intermittent jerks of the legs or arms, which occur as the individual enters slow wave sleep, and can cause arousal from sleep. Other people have episodes in which their muscles fail to be paralyzed during REM sleep, and they act out their dreams. This REM behavior disorder can also be very disruptive to a normal nights’ sleep. Both disorders are more common in people with Parkinson’s disease, and both can be treated with drugs that treat Parkinson’s, or with an anti-epileptic drug called clonazepam.

Narcolepsy is a relatively uncommon condition (one case per 2,500 people) in which the switching mechanism for REM sleep does not work properly. Narcoleptics have sleep attacks during the day, in which they suddenly fall asleep. This is socially disruptive, as well as dangerous, for example, if they are driving. They tend to enter REM sleep very quickly as well, and may even enter a dreaming state while still awake, a condition known as hypnagogic hallucinations. They also have attacks during which they lose muscle tone, similar to what occurs during REM sleep, but while they are awake. Often, this occurs while they are falling asleep or just waking up, but attacks of paralysis known as cataplexy can be triggered by an emotional experience or even hearing a funny joke.

Recently, insights into the mechanism of narcolepsy have given major insights into the processes that control these mysterious transitions between waking, slow wave and REM sleep states. (From Brain Facts: a Primer on the Brain and Nervous System, 2002)

Exercise 4. Work in small groups. Write out from the text 15 key word combinations which will help you to retell the text and explain your choice. Then together agree on the final list of word combinations.

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