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What
is Narcolepsy?
Narcolepsy is a chronic neurological disorder
caused by the brain's inability to regulate
sleep-wake cycles normally. At various
times throughout the day, people with
narcolepsy experience fleeting urges to
sleep. If the urge becomes overwhelming,
patients fall asleep for periods lasting
from a few seconds to several minutes.
In rare cases, some people may remain
asleep for an hour or longer.
Narcoleptic sleep episodes can occur at
any time, and thus frequently prove profoundly
disabling. People may involuntarily fall
asleep while at work or at school, when
having a conversation, playing a game,
eating a meal, or, most dangerously, when
driving or operating other types of potentially
hazardous machinery. In addition to daytime
sleepiness, three other major symptoms
frequently characterise narcolepsy: cataplexy,
or the sudden loss of voluntary muscle
tone; vivid hallucinations during sleep
onset or upon awakening; and brief episodes
of total paralysis at the beginning or
end of sleep.
Contrary to common beliefs, people with
narcolepsy do not spend a substantially
greater proportion of their time asleep
during a 24-hour period than do normal
sleepers. In addition to daytime drowsiness
and involuntary sleep episodes, most patients
also experience frequent awakenings during
nighttime sleep. For these reasons, narcolepsy
is considered to be a disorder of the
normal boundaries between the sleeping
and waking states.
For most adults, a normal night's sleep
lasts about 8 hours and is composed of
four to six separate sleep cycles. A sleep
cycle is defined by a segment of non-rapid
eye movement (NREM) sleep followed by
a period of rapid eye movement (REM) sleep.
The NREM segment can be further divided
into stages according to the size and
frequency of brain waves. REM sleep, in
contrast, is accompanied by bursts of
rapid eye movement (hence the acronym
REM sleep) along with sharply heightened
brain activity and temporary paralysis
of the muscles that control posture and
body movement. When subjects are awakened
from sleep, they report that they were
"having a dream" more often
if they had been in REM sleep than if
they had been in NREM sleep. Transitions
from NREM to REM sleep are governed by
interactions among groups of neurons (nerve
cells) in certain parts of the brain.
Scientists now believe that narcolepsy
results from disease processes affecting
brain mechanisms that regulate REM sleep.
For normal sleepers a typical sleep cycle
is about 100 - 110 minutes long, beginning
with NREM sleep and transitioning to REM
sleep after 80 - 100 minutes. But, people
with narcolepsy frequently enter REM sleep
within a few minutes of falling asleep.
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