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CEREBRUM
The cerebrum is the largest part of the brain, consist of two cerebral
hemispheres which are connected by a mass of white matter called the
corpus callosum and is situated in the anterior and middle cranial fossa of
the skull occupying the whole concavity of the vault of the skull,
posteriorly the cerebrum lies above the tentorium cerebelli.
The cerebrum may be divided into two parts:
 Diencephalon which form the central core.
 Telencephalon which form the cerebral hemisphere
The cerebral hemisphere is separated by a deep midline sagittal fissure,
the longitudinal cerebral fissure. The fissure contains the sickle-shaped
fold of dura mater called the falx cerebri, and the anterior cerebral
vessels.
In the depth of the fissure, the great commisure, the corpus callosum
connects the hemisphere across the midline.
A second fold of dura mater separates the cerebral hemisphere from the
cerebellum and is called the tentorium cerebelli.
In order to increase the surface area of the cerebral cortex maximally, the
surface of each cerebral hemisphere is thrown into folds or gyri, which
are separated from each other by sulci or fissures.
Each hemisphere divided into lobes which are named according to the
cranial bones under which they lie. The central and parieto-occipital
sulci and the lateral and calcarine sulci are boundaries used for the
division of the cerebral hemisphere into frontal, parietal, temporal, and
occipital lobes.
Main Sulci
1-central sulcus:
Is of great importance because the gyrus that anterior to it contains the
motor cells (motor area) that initiate the movement of the opposite side
of the body.
Posterior to the central sulcus lies the general sensory cortex (sensory
area) that receives sensory information from the opposite side of the
body.
2-lateral sulcus:
Is a deep cleft on the inferior and lateral surface of the cerebral
hemisphere.
An area called insula lies at the bottom of the deep lateral sulcus and
cannot be seen from the surface unless the lips of the sulcus are separated.
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3-parieto-occipital sulcus:
Begin on the superior medial margin of the hemisphere about 2 inches
(5cm) anterior to the occipital pole. It passes downward and anteriorly on
the medial surface to meet the calcarine sulcus.
4-calcarine sulcus:
It commences under the posterior end of the corpus callosum and arches
upward and backward to reach the occipital pole.
The calcarine sulcus is joined at an acute angle by the parieto-occiptal
sulcus about halfway along its length.
Lobes of the cerebral hemisphere
A-superolateral surface of hemisphere:
1-FRONTAL LOBE:
Occupy the area anterior to central sulcus and superior to the lateral
sulcus.
The superolateral surface of the frontal lobe is divided by three sulci into
four gyri. The precentral sulcus runs parallel to the central sulcus and the
precentral gyrus lies between them. Extending anteriorly from the
precentral sulcus are the superior and inferior frontal sulci. The superior
frontal gyrus lies superior to the superior frontal sulcus, middle frontal
gyrus lies between the superior and inferior sulci, and the inferior frontal
gyrus lies inferior to the inferior frontal sulcus.
2-PARIETAL LOBE:
Occupies the area posterior to the central sulcus and superior to the lateral
sulcus, it extend posteriorly as far as the parieto-occipital sulcus.
The lateral surface of parietal lobe is divided by two sulci into three gyri.
Post central sulcus runs parallel to the central sulcus and the post central
gyrus lies between them. Running posteriorly from the middle of post
central sulcus is the intra parietal sulcus. The intra parietal sulcus has
superior to it the superior parietal lobule (gyrus) and inferior to it the
inferior parietal lobule (gyrus).
3-TEMPORAL LOBE:
Occupies the area inferior to the lateral sulcus.
The lateral surface of the temporal lobe is divided into three gyri by two
sulci.
The superior and middle temporal sulci run parallel to the posterior
ramus of the lateral sulcus, and divided the temporal lobe into the
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superior. Middle, and inferior gyri, the inferior temporal gyrus continued
onto inferior surface of the hemisphere.
4-OCCIPITAL LOBE:
Occupies the small area behind the parieto-occipital sulcus.
B-Medial and inferior surface of hemisphere:
There are many important areas that should be recognized, include:
1-corpus callosum: which is the largest commissure of the brain,
connects two cerebral hemisphere.
2-cingulate gyrus: begins beneath the anterior ends of the corpus
callosum and continue above the corpus callosum until it reaches its
posterior end. The gyrus is separated from the corpus callosum by the
callosal sulcus.
The cingulated gyrus is separated from the superior frontal gyrus by the
cingulate sulcus.
3-paracentral lobule: is the area of the cerebral cortex that surrounds the
indentation produced by the central sulcus on the superior border.
4-precuneus: is an area of cortex bounded anteriorly by the upturned
posterior end of the cingulate sulcus and posteriorly by the parietooccipital sulcus.
5-cuneus: is a triangular area of cortex bounded above by a parietooccipital sulcus, inferiorly by the calcarine sulcus, and posteriorly by the
superior medial margin.
6-Collateral sulcus: run anteriorly below the calcarine sulcus.
7-lingual gyrus: run between the collateral sulcus and calcarine sulcus.
8-parahippocampal gyrus: lies anterior to the lingual gyrus and
terminate in front as the hook like uncus.
9-medial occipito-temporal gyrus: extend from the occipital pole to the
temporal pole.
10-olfactory sulcus, it run on the inferior surface of the frontal lobe, the
olfactory bulb and tract overlie a sulcus called the olfactory sulcus.
Medial to the olfactory sulcus is the gyrus rectus and lateral to the sulcus
are a number of orbital gyri.
Functional localization of cerebral cortex:
The cerebral cortex functionally is divided into different areas of
specialization, as shown below:
1-frontal lobe: have the following specialized centers:
A-Motor area: situated in the precentral gyrus in the anterior wall of the
central sulcus.
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The motor area if electrically stimulated it initiate the motor movement in
the opposite side of the body.
B-Frontal eye field: situated in the middle frontal gyrus.this area concern
with control the conjugate movements of the eyes especially towards the
opposite side.
C-Motor speech area (Brocas area): located in the inferior frontal gyrus
and in the majority of individuals, this area is situated on the left or
dominant hemisphere and ablation will result in paralysis of speech.
The ablation of this region in the non dominant hemisphere has no effect
on speech.
D-Prefrontal cortex: is an extensive area that lies anterior to the
precentral area. it includes the greater parts of the superior, middle, and
inferior frontal gyri, the orbital gyri, and most of the medial frontal gyrus.
Prefrontal area is concerned with the makeup of the individual's
personality.
2-parietal lobe: contain the sensory area occupying the post central
gyrus
Sensory area is concerned with sensory information from the opposite
side of the body so lesion of this area results in contralateral sensory
disturbance.
3-occipital lobe contain the visual area that located in the posterior
part of calcarine sulcus.
Visual area is concerned with visual field activity
4-temporal lobe: contain the following areas:
A-Auditory area: located in the inferior wall of the lateral sulcus and it
concerned with hearing function so a unilateral lesion result in the
contralateral hearing loss.
B-Sensory speech area (Wernickes area): localized in the left dominant
hemisphere, mainly in the superior temporal gyrus.
Wernicks area permits the understanding of the written and spoken
language.
So lesion of this area produces a loss of ability to understand the spoken
and written words that is called receptive aphasia.
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