of progressively greater “depth”, with
slowing of brain activity. In REM sleep,
the brain becomes more active; the
eyes move rapidly and
Sleep is a fundamental human need, as
shown by the effects of
although its purpose is not understood
in detail. The need for sleep varies from
person to person and decreases with age.
Sleep disorders include difficulty in
falling or remaining asleep (see
); difficulty in staying awake (see
disruption of sleep by
bed-wetting, night terrors,
. (See also
sleep apnoea A disorder in which there
are episodes of temporary cessation of
seconds or longer)
People with sleep apnoea may not be
aware of any problem during the night,
but they may be sleepy during the day,
with poor memory and concentration.
Severe sleep apnoea is potentially seri-
ous and may lead to
failure, myocardial infarction,
Obstructive sleep apnoea is the most
common type and may affect anyone,
but more often middle-aged men, espe-
cially those who are overweight. The
most common cause is over-relaxation
of the muscles of the soft
, which obstructs the passage of
air. Obstruction may also be caused by
tion causes snoring. If complete blockage
occurs, breathing stops. This triggers
the brain to restart breathing, and the
person may gasp and wake briefly.
In central sleep apnoea, breathing stops
because the chest and
temporarily cease to work, probably
due to a disturbance in the brain's con-
trol of breathing. Causes include paralysis
of the diaphragm and disorders of the
. Snoring is not a main feature.
People who are overweight may find
losing weight helps. Alcohol and sleep-
ing drugs aggravate sleep apnoea. In
one treatment, air from a compressor is
forced into the airway via a mask worn
over the nose. Night-time artificial
may be needed.
, or surgery to shorten or
stiffen the soft palate may be performed.
sleep deprivation Insufficient
tability and a shortened attention span
may occur after a short night's sleep.
Longer periods without sleep leave a
person increasingly unable to concen-
trate or perform normal tasks. Three or
more sleepless nights may lead to
and, in some cases, to
sleeping drugs A group of drugs used
and chloral hydrate. Sleeping drugs may
cause drowsiness and impaired concen-
tration on waking. Long-term use may
sleeping sickness A serious infectious
disease of tropical Africa caused by the
which is transmitted to humans by the
bites of tsetse flies.
One form of the disease, which occurs
in West and Central Africa, takes a slow
course, with bouts of fever and lymph
node enlargement. After months or years,
spread to the brain occurs, causing head-
aches, confusion, and, eventually, severe
lassitude. Without treatment, coma and
death follow. The other, East African,
form runs a faster course. Fever devel-
ops after a few weeks of infection, and
effects on the heart may be fatal before
the disease has spread to the brain.
Drugs can effect a cure, but there may
be residual brain damage if the infec-
tion has already spread to the brain.
sleep paralysis The sensation of being
unable to move at the moment of going
to sleep or when waking up, usually
lasting only a few seconds. It may be
paralysis most often occurs in people
. (See also
sleep terror See
sleepwalking Walking while asleep.
Sleepwalking is usually calm and aim-
less, although it is sometimes more
frantic when it occurs with
Some people regularly sleepwalk. Sleep-
walking in children is not normally a
cause for concern and tends to disap-
pear with age. In adults, it may be related
to anxiety or the use of sleeping drugs.
sling A triangular bandage used to
immobilize, support, or elevate an arm.