MEMBRANE
MENINGIOMA
types of
breast cancer
and ovarian can-
cer (see
ovary, cancer
of).
Possible adverse effects include nausea,
vomiting, sore throat, loss of appetite,
aplastic
anaemia
,
abnormal bleeding,
and increased susceptibility to infection.
membrane
A layer of tissue that covers
or lines a body surface or forms a barrier.
memory
The ability to remember. Mem-
ory is usually thought of as having 3
stages: registration, storage, and recall.
In registration, information is perceived,
understood, and stored in short-term
memory. Unless they are constantly
repeated, the contents of short-term
memory are lost in minutes. In reten-
tion, important information is transferred
into long-term memory and stored.
Recall involves bringing information
into the conscious mind at will.
Many factors determine how well
something is remembered, including its
familiarity and how much attention has
been paid to it.
It is not known where in the brain the
memory process takes place. However,
the temporal lobe and
limbic system
may be involved. The mechanisms for
storing memory are also unknown.
Most memory disturbances are due to
failure at the retention or recall stage
(see
amnesia
). In some cases, the prob-
lem occurs at the registration stage.
Some people with
temporal lobe epi-
lepsy
have uncontrollable flashbacks of
distant past events. The most common
memory disorder is the normal diffi-
culty in recall that develops with age.
More severe loss of memory may be an
early symptom of
dementia
.
memory, loss of
See
amnesia
.
menarche
The onset of
menstruation
.
Menarche usually occurs around age 13,
2 or 3 years after
puberty
starts.
Meniere's disease
An inner
ear
disor-
der characterized by recurrent
vertigo
,
deafness
,
and
ti
^
itus
.
The cause is a
build-up of fluid in the
labyrinth
. The
fluid build-up may damage the labyrinth
and sometimes the adjacent
cochlea
.
The disease is uncommon before the
age of 40. There is a sudden attack of
vertigo, lasting from a few minutes to
several hours. This is usually accompa-
nied by nausea, vomiting,
nystagmus
,
and deafness, tinnitus, and a feeling of
pressure or pain in the affected ear.
Diagnosis is usually made with audi-
ometry (see
hearing tests
) or other
hearing tests, and a
caloric test
. Treat-
ment with certain
antihistamine drugs,
such as
cinnarizine
,
or with
betahistine
usually relieves the symptoms, although
prochlorperazine
may be given, either
rectally or by injection,
for severe
attacks. Meniere's disease can also be
treated by surgery to the inner ear if
symptoms are not controlled by drugs.
If deafness eventually becomes total,
the other symptoms usually disappear.
meninges
The 3 membranes that cover
and protect the
brain
and the
spinal
cord
. The outer membrane, the dura
mater, is tough and fibrous; it lines the
inside of the skull and forms a loose
sheath around the spinal cord. The
middle membrane, the arachnoid mater,
is elastic and web-like. The inner mem-
brane, the pia mater, lies directly next
to the brain. It is separated from the
arachnoid mater by the subarachnoid
space, which contains
cerebrospinal fluid
.
M ENINGES
meningioma
A rare, noncancerous tu-
mour of the
meninges
of the brain that
arises from the arachnoid mater (middle
layer) and usually becomes attached to
the dura mater (outer layer). The tumour
slowly expands and may become very
large before any symptoms appear.
Symptoms can include headache, vom-
iting, and impaired mental function.
362
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