Bma Illustrated Medical Dictionary

types of breast cancerand 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.

membraneA layer of tissue that covers

or lines a body surface or forms a barrier.

memoryThe 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 ofSee amnesia.

menarcheThe onset of menstruation.

Menarche usually occurs around age 13,

2 or 3 years after pubertystarts.

Ménière’s diseaseAn inner eardisor-

der characterized by recurrent vertigo,

deafness, and tinnitus. 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

prochlorperazinemay be given, either

rectally or by injection, for severe

attacks. Ménière’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.

meningesThe 3 membranes that cover

and protect the brainand 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.

meningiomaA rare, noncancerous tu-

mour of the meningesof 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.

MEMBRANE MENINGIOMA

M

MENINGES

Dura mater

Meninges

Skull Grey matter of brain

White matter

of brain

LOCATION

Arachnoid

mater

Pia mater