Preventive measures should be taken in
any area where mosquitoes are ram-
pant. The most effective measures are
wearing long sleeves and socks, placing
mosquito screens over windows, and
using insect-repellent sprays or slow-
burning coils that release insecticidal
smoke. Mosquito nets should be placed
over beds. (See also insect bites;insects
and disease.)
motion sicknessA condition that some
people experience during road, sea,
or air travel. Symptoms range from un-
easiness and headache to distress,
excessive sweating and salivation, pal-
lor, nausea, and vomiting.
Motion sickness is caused by the effect
of repetitive movement on the organ of
balance in the inner ear. Factors such as
anxiety, a fume-laden atmosphere, or
the sight of food may make the condi-
tion worse. So, too, can focusing on
nearby objects; sufferers should look at
a point on the horizon.
Motion sickness may be prevented or
controlled by antiemetic drugsor by
acupressure bands worn on the wrist.
motorA term used to describe anything
that brings about movement, such as a
muscleor a nerve.
motor neuron diseaseA group of dis-
orders in which there is degeneration
of the nervesin the central nervous sys-
temthat control muscular activity. This
causes weakness and wasting of the
muscles. The cause is unknown.
The most common type of motor neu-
ron disease is amyotrophic lateral
sclerosis (ALS or Lou Gehrig’s disease).
It usually affects people over the age of
50 and is more common in men. Some
cases run in families. Usually, symp-
toms start with weakness in the hands
and arms or legs, and muscle wasting.
There may be irregular muscle contrac-
tions, and muscle cramps or stiffness.
All four extremities are soon affected.
Progressive muscular atrophy and pro-
gressive bulbar palsy both start with
patterns of muscle weakness different
from ALS but usually develop into ALS.
There are 2 types of motor neuron dis-
ease that first appear in childhood or
adolescence. In most cases, these con-
ditions are inherited. Werdnig–Hoffmandiseaseaffects infants at birth or soon
afterwards. In almost all cases, progres-
sive muscle weakness leads to death
within several years. Chronic spinal
muscular atrophy begins in childhood or
adolescence, causing progressive weak-
ness but not always serious disability.
There are no specific tests for motor
neuron disease. Diagnosis is based on
careful clinical examination by a neurol-
ogist. Tests including EMG, muscle
biopsy, blood tests, myelography, CT
scanning, or MRImay be performed.
The disease typically goes on to affect
the muscles involved in breathing and
swallowing, leading to death within 2–4
years. However, about 10 per cent of
sufferers survive for 10 years.
Nerve degeneration cannot be slowed
down, but physiotherapyand the use of
various aids may help to reduce dis-
ability. The drug riluzole is used to
extend life (or the time until mechanical
ventilationis required).
mouldAny of a large group of fungithat
exist as many-celled, filamentous col-
onies.Some moulds are the source of
antibiotic drugs. Others can cause dis-
eases such as aspergillosis.
mountain sicknessAn illness that can
affect people who have ascended rapidly
to heights above 2,400m–3,000m.Moun-
tain sickness is caused by the reduced
atmospheric pressure and oxygen levels
that occur at high altitude.
mouthThe oral cavity, which breaks
food down for swallowing (see masti-
cation) and is used in breathing. In
addition, it helps to convert sound
vibrations from the larynxinto speech.
mouth cancerForms of cancerous
tumour that affect the lips, tongue, and
oral cavity. Lip cancer and tongue can-
cer are the most common types.
Predisposing causes of mouth cancer
are poor oral hygiene, drinking alcoholic
spirits, tobacco-smoking, chewing tob-
acco, and inhaling snuff. Irritation from
ill-fitting dentures or jagged teeth are
other factors. Men are affected twice as
often as women; most cases occur in
men over the age of 40.
Mouth cancer usually begins with
a whitish patch, called leukoplakia, or a
small lump. These may cause a burningMOTION SICKNESS MOUTH CANCERM