BRAIN ABSCESS
Bowman’s capsule
A cup-shaped membrane within the
kidney’s
nephron
containing a
glomeru-
lus
(a cluster of tiny blood vessels called
capillaries). Here, blood is filtered into
the kidney tubule.
BP
The abbreviation for
blood pressure.
brace, dental
See
orthodontic appliances.
brace, orthopaedic
An appliance worn to support part of
the body or hold it in a fixed position. A
brace may be used to correct or halt the
development of a deformity, to aid
mobility, or to relieve pain. (See also
caliper splint; corset; splint.)
brachial artery
The
artery
that runs down the inner side
of the upper arm, between the armpit
and the elbow.
brachialgia
Pain or stiffness in the arm that is often
accompanied by pain, tingling and/or
numbness of the hands or fingers, and
weak hand grip. It may be a symptom
of underlying disorders such as
frozen
shoulder
or nerve compression from
cer-
vical osteoarthritis
.
brachial plexus
A group of large nerve trunks formed
from nerve roots of the lower part of
the cervical spine (in the neck) and
upper part of the thoracic spine (in the
chest). These nerve trunks divide into
the musculocutaneous, axillary, median,
ulnar, and radial nerves, which control
muscles in and receive sensation from
the arm and the hand. Injuries to the
brachial plexus can cause loss of move-
ment and sensation in the arm.
In severe injuries, there may be dam-
age to both the upper and the lower
nerve roots of the brachial plexus, pro-
ducing complete paralysis of the arm.
The paralysis may be temporary if the
stretching was not severe enough to
tear nerve fibres. It may be possible to
repair nerve roots that have been torn
by nerve grafting, which is a
micro-
surgery
procedure, but if a nerve root
has become separated from the spinal
cord, surgical repair will not be success-
ful. Apart from injuries, the brachial
plexus may be compressed by the pres-
ence of a
cervical rib
(extra rib).
brachytherapy
A type of
radiotherapy.
bradycardia
An abnormally slow heart rate. Most
people have a heart rate of between 60
and 100 beats per minute. Many ath-
letes and healthy people who exercise
regularly and vigorously have slower
rates. In others, bradycardia may indi-
cate an underlying disorder such as
hypothyroidism
or
heart block.
Bradycar-
dia may also occur as a result of taking
beta-blocker drugs.
Profound or sudden
bradycardia may cause a drop in blood
pressure that results in fainting (see
vasovagal attack).
bradykinin
A
polypeptide
(protein molecule) that
forms naturally in the blood as part of
the inflammatory process. Bradykinin is
a powerful vasodilator (it causes the
widening of blood vessels). Bradykinin
also allows fluid to leak from the blood
vessels; stimulates pain receptors; and
causes contraction of the smooth mus-
cle in internal organs such as the lungs
or intestines.
Braille
A
system
of
embossed
dots,
now
accepted for all written languages, that
enables blind people to read and write.
The system is based on six raised dots,
which can be combined in different
ways to form symbols.
There are two types of Braille. In
grade I, each symbol represents an indi-
vidual letter or punctuation mark. In
grade II, which is the more widely
used, symbols represent common letter
combinations or words.
brain
The major organ of the
nervous system
,
located in the
cranium
(skull). The brain
receives, sorts, and interprets sensations
from the nerves that extend from the
central nervous system
(brain and spinal
cord) to the rest of the body; it initiates
and coordinates nerve signals involved
in activities such as speech, movement,
thought, and emotion.
An adult brain weighs about 1.4 kg
and has three main structures: the
brain-
stem;
the
cerebellum;
and the largest part,
the
cerebrum,
which consists of left and
right hemispheres.
CEREBRUM
Each hemisphere in the cerebrum has
an outer layer called the cortex, consist-
ing of grey matter, which is rich in
nerve-cell bodies and is the main region
in the brain for conscious thought, sen-
sation,
and movement.
Beneath
the
cortex are tracts of nerve fibres called
white matter, and, deeper within the
hemispheres, are the
basal ganglia
(paired
nerve cell clusters). The surface of each
of the hemispheres is divided by fissures
(sulci) and folds (gyri) into distinct
lobes (occipital, frontal, parietal, and
temporal lobes), named after the skull
bones that overlie them. A thick band of
nerve fibres called the corpus callosum
connects the hemispheres.
The
cerebrum
encloses
a
central
group of structures including the
thalami
and the
hypothalamus,
which has close
connections with the
pituitary gland
.
Encircling the thalami is a complex of
nerve centres called the
limbic system.
These structures act as links between
parts of the cerebrum and the brain-
stem lying beneath the thalami.
BRAINSTEM AND CEREBELLUM
The brainstem
is
concerned mainly
with the control of vital functions such
as breathing and blood pressure. The
cerebellum at the back of the brain con-
trols balance, posture, and muscular
coordination. Both of these regions op-
erate at a subconscious level.
MENINGES AND CEREBROSPINAL FLUID
The brain and spinal cord are encased
in three layers of membranes known as
meninges
.
Cerebrospinal fluid
circulates
between these membrane layers and
within the four main brain cavities,
which are known as ventricles.This fluid
helps to nourish and cushion the brain.
BLOOD SUPPLY
The brain as a whole has an extensive
blood supply. Blood comes from a circle
of arteries fed by the internal
carotid
arteries
(which run up each side of the
front of the neck to enter the base of
the skull) and from two vertebral arter-
ies that run parallel to the spinal cord.
The brain receives about 20 per cent of
the blood from the heart’s output.
brain abscess
A collection of pus, surrounded by
inflamed tissues, within the brain or on
its surface. The most common sites are
the frontal and temporal lobes of the
cerebrum
in the forebrain.
Brain abscesses may occur after a
head injury, but most cases result from
the spread of infection from elsewhere
in the body, such as the middle ear or
the sinuses. Another cause of a brain
B
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