BRAIN ABSCESS
B
STRUCTURE OF THE BRAIN
The brain has three main parts:
the brainstem (an extension of the
spinal cord), the cerebellum, and
the cerebrum, much of which
consists of the two large cerebral
hemispheres. Each hemisphere
consists of an outer layer, or cortex,
which is rich in nerve cells and called
grey matter, and inner areas rich in
nerve fibres, called white matter.
The surface of each hemisphere
is thrown into folds called gyri,
separated by fissures called sulci.
The two hemispheres are linked by a
thick band of nerve fibres, the corpus
callosum. Deep within the forebrain
are various central structures, which
include the thalamus, hypothalamus,
basal ganglia, and pituitary gland.
The brain has the consistency of
jelly and, in adults, weighs about
1.4
kg. It is protected by membranous
coverings (known as meninges)
within the skull.
F r o n t a l l o b e
Lobes
These are broad
surface regions of
each hemisphere that
are named after the
overlying bones of
the skull. The four main
regions are the frontal,
parietal, temporal, and
occipital lobes.
M u s c le
A b s t r a c t t h o u g h t
Special areas
Some areas ofthe brain
are associated with
specific functions - for
example, the occipital
lobe with vision and the
cerebellum with balance
and coordination. Touch
and pressure sensation
is perceived within the
postcentralgyrus.
Muscle movements
are controlled from the
precentral gyrus;
speech is controlled
from an area in the
frontal lobe ofthe
dominant hemisphere.
IMAGING THE BRAIN
CT scanning
CT scans produce images as “slices” through
the head. The scan above shows bleeding into
the brain tissue (a cerebral haemorrhage).
Angiography
This technique makes blood vessels clearly
visible. The angiogram above shows the carotid
artery and its branches.
Magnetic resonance imaging
MRI produces three-dim ensional or cross-
sectional images. This MRI shows a tumour (the
white area to the right of centre) in the cerebellum.
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