Mechanism of demyelination
The fatty myelin sheaths that surround and insulate
nerve fibres break down, causing the affected
nerves to “short-circuit”.
ing the brain and the spinal cord, or
may be part of the
w hich links the CNS to sense
receptors, muscles, glands, and other
organs throughout the body.
Patches of demyelination are visible
scans of the brain in people
with symptoms that include blurred
vision, muscle weakness, and loss of
coordination. The cause of the demy-
elination in multiple sclerosis is not
known. In many cases of the disease,
with periods of partial or complete
recovery of nerve function.
In the rare disorder
there is inflammation of nerve cells in
the CNS and sometimes also areas of
demyelination along the nerves.
A type of
transparent dome that forms the front
of the eyeball) with threadlike exten-
sions that branch out from the centre.
Dendritic ulcers are commonly due to
infection w ith
The loss of the
supply to an area
of skin, a muscle, an organ, or another
body part. Nerves may be damaged by
injury or by disease, or as a result of
surgery. A denervated area loses all
sensation, and its functioning may be
impaired; for example, muscles may
become paralysed. In some cases, the
affected nerves may regrow, but often
the damage is permanent.
A tropical disease caused by a virus
spread by the mosquito A
The symptoms include fever, headache,
rash, and joint and muscle pains, w hich
often subside after about three days.
dengue. Prevention involves protection
against mosquito bites (see
An imaging technique that uses low-
to measure bone density, as
determined by the
calcified material w ithin bone tissue.
Densitometry is used to diagnose and
assess the severity of
ing away of bone tissue), especially in
the spine and the femur (thigh bone),
and to assess its response to treatment.
passed through the body. A computer
assesses the amount of X-rays absorbed
by the body and uses this information
to calculate the bone density.
defined as its mass per unit volume.
In radiology, the term relates to the
amount of radiation absorbed by the
structure being X-rayed. Bone absorbs
radiation well and appears white on X-
ray film. A lung, w hich contains mostly
air, absorbs little radiation and is dark
on the film. The same is true for
Injuries or disorders of the teeth and
gums that require immediate treatment
because of severe pain and/or because
delay could lead to poor healing or to
complications. A tooth that has become
dislodged by injury can be reimplanted
) into the gum
successfully if this is done without
delay, usually w ithin 3 0 minutes of the
injury. A partly dislodged tooth should
be manipulated back into the socket in
the gum immediately.
SCOPE OF DENTAL EXAMINATION
A dental examination includes an
During the dental
dentist checks for the
presence or absence
of individual teeth.
Any abnormalities and
all fillings are recorded
The dentist uses a mirror
to see the backs ofthe
teeth and into the back
ofthe mouth; a metal
instrument is used to
probe for dental cavities
or chipped teeth.
M ir r o r
. P r o b e