Sleep - biology.

« V FUNCTIONS OF SLEEP Although no one knows for sure why we sleep, there are a number of theories.

Sleep may have evolved to protect animals from their predators by reducing theiractivity during the times when they are most vulnerable. Research has shown that REM and NREM sleep may serve specific biological functions.

Sleep deprivation studies reveal that humans and other animals respond to sleeploss in the same way.

When study subjects are deprived of REM sleep, they tend to spend longer periods in REM sleep during their next sleeping period to make up forthe loss.

REM sleep after deprivation is more intense, with more eye movements per minute than in normal REM sleep.

Similarly, subjects deprived of NREM sleepusually spend more time in NREM sleep afterward.

EEGs measuring brain activity show that this rebound NREM sleep also differs from normal NREM sleep.

This researchsuggests that the body needs adequate levels of both REM and NREM sleep.

This conclusion has led many sleep researchers to believe that the two kinds of sleep servedifferent biological purposes, although the exact functions remain unclear. The relationship between maturity at birth and REM sleep suggests that REM sleep plays a role in the development of the brain.

REM sleep may have a related functionlater in life as well.

However, that function remains a mystery. VI SLEEP DISORDERS People who suffer from the most common sleep disorder, insomnia, have difficulty falling or staying asleep.

Sleepiness caused by insomnia reduces concentration andslows reaction time during waking hours, leading to reduced productivity and accidents.

One in three adults experiences some degree of insomnia at one time oranother, especially during periods of stress.

Longer-lasting cases of insomnia, called chronic insomnia, are less common and may be caused by a number of factors inaddition to stress, including imbalances in body chemistry or other medical conditions. Taken under the guidance of a qualified physician, sleeping pills are an effective treatment for temporary insomnia and may help some chronic insomnia patients.

Insome cases of insomnia, psychological treatments and physical exercise programs help patients identify or manage stress, enabling them to sleep better.

Recent workhas suggested that melatonin, a hormone naturally released into the bloodstream during the hours of darkness, may play a role in synchronizing sleep to a 24-hourcycle.

Results from studies of the effects of melatonin on human sleep have been inconsistent.

However, some evidence suggests that supplements of this hormonecombat insomnia in older people who are melatonin deficient. Narcolepsy is a sleep disorder that affects both NREM sleep and REM sleep mechanisms.

Narcoleptics are persistently sleepy and experience periodic losses of muscletone called cataplexy.

During cataplectic attacks, the narcoleptic’s muscles weaken, and if the attack is severe, the narcoleptic falls to the ground.

Cataplectic attacksare triggered by sudden strong emotional reactions, such as laughter.

A related symptom, called sleep paralysis, can occur when the narcoleptic is lying down, prior tofalling asleep or just after awakening.

At these times the person may lose muscle tone, resulting in an apparent paralysis, while remaining fully awake.

Sleep paralysiscan be terrifying if the narcoleptic does not realize that it is not life threatening.

Animal studies have shown that the loss of muscle tone experienced by narcoleptics inwaking results from an activation of the REM sleep-active and an inactivation of the REM sleep-inactive systems that normally function to reduce muscle tone in REMsleep.

Narcoleptics are treated with stimulants to block sleepiness and with REM sleep suppressants to block cataplexy. Children often experience one of several sleep disorders.

Nocturnal enuresis, commonly known as bedwetting, typically occurs during NREM sleep.

Sleep talking andsleepwalking also usually occur during NREM sleep ( see Somnambulism).

Night terrors, typically marked by a scream and a terrified, confused awakening, affect many children.

These disorders do not indicate any serious neurological or behavioral problem.

Children suffering from them usually outgrow them by puberty, although sleeptalking and sleepwalking may persist into adulthood. In another common disorder, sleep apnea, relaxation of the muscles of the tongue and the soft palate at the base of the throat, allows the breathing passage tocollapse in individuals with a narrow airway.

Although chest movements may continue, no air flows into the lungs and oxygen levels in the blood decrease.

When bloodoxygen levels fall too low, the person briefly wakes to take a breath.

This gasping breath can produce a loud, characteristic snort.

The cycle of sleeping, airwaycollapsing, waking, and sleeping repeats, often hundreds of times in a night.

Individuals with sleep apnea do not remember these brief awakenings and believe theyslept through the night.

However, the interrupted sleep leaves the individual exhausted in the morning and sleepy throughout the day.

If left untreated, sleep apneamay also cause cardiovascular problems and greatly shorten life span.

Effective treatments are available at medical centers specializing in sleep disorders.

Onetreatment, called continuous-positive-airway-pressure (CPAP), uses a mask to deliver a stream of air through the nose, preventing airway collapse, restoring normalsleep.

Sometimes surgical treatments that enlarge the airway can be effective. Contributed By:Jerome M.

SiegelMicrosoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation.

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