BRAILLE
BRAIN
B
bradycardia may cause a drop in blood
pressure that results in fainting (see
vasovagal attack).
B raille A system of embossed dots,
now accepted for all written languages,
that enables blind people to read and
write. The system is based on 6 raised
dots, which can be combined in differ-
ent ways. There are 2 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 com-
binations or words.
b ra in 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 3 main structures: the largest part,
the
cerebrum,
consisting of left and
right hemispheres; the
brainstem;
and
the
cerebellum
. Each hemisphere in the
cerebrum has an outer layer called the
cortex, consisting of grey matter, which
is rich in nerve-cell bodies and is the
main region for conscious thought, sen-
sation, and movement.
Beneath the
cortex are tracts of nerve fibres called
white matter, and, deeper within the
hemispheres, the
basal ganglia.
The sur-
face of each hemisphere is divided by
fissures (sulci) and folds (gyri) into dis-
tinct 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 that includes 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 brainstem
lying beneath the thalami.
The brainstem is concerned mainly
with the control of vital functions such as
breathing and blood pressure. The cere-
bellum at the back of the brain controls
BRAIN
Meninges
Cerebral cortex
Cerebrum
Corpus
callosum
Hypothalamus
Pituitary gland
Cerebrospinal fluid
Midbrain
Brainstem
Pons
Medulla
Spinal cord
90
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