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Neuro-Anatomy
Lec: 7&8 Prof Dr. Al-Hubaity
The cerebrum consists of 2 hemispheres which are partially separated from
each other by the longitudinal cerebral fissure, but are connected together at
the bottom of the fissure by a thick mass of commissural fibers called the
corpus callosum
Each hemisphere has 3 surfaces:
1- Superolateral surface: convex and lies in contact with the roof and
side of the skull.
2- Medial surface: flat & lies in contact with the falxcerebri.
3- Inferior surface: lies in contact with the floor of anterior and middle
cranial fossae and rests posteriorly on the tentorium cerebelli. This
surface includes orbital &tentorial parts.
Each hemisphere has 3 poles, frontal, temporal and occipital poles
each hemisphere is divided into 4 lobes by 3 sulci, these lobes are frontal,
parietal, temporal and occipital lobes and the sulci are central, lateral and
parieto-occipital sulcus.
Each gyrus consists of a central core of white matter covered by a layer of
gray matter.
The gray matter on the surface of the cerebrum forms the cerebral cortex
which consists of nerve cells arranged in 6 layers.
The gyri vary in direction and also possess different functional areas e.g,
motor, general sensory, visual, olfactory & auditory.
The sulci vary in depth, some of them are very shallow, while others are
very deep and may indents the walls of the lateral ventricle as the calcarine
and collateral sulci.
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Sulci &gyri on the lateral surface(outer surface) of the cerebral
hemisphere:
1- Central sulcus, passes on the superolateral surface downward and
forward, to end a short distance above the posterior ramus of the
lateral sulcus, it separate the frontal lobe from the parietal lobe and
thus it separates the motor area (in the pre central gyrus) from the
sensory area (in the post central gyrus).
2- Lateral sulcus, separates the frontal & parietal lobes from the temporal
lobe. It is related to the middle cerebral artery. At the bottom of the
fissure is the insula of the brain. The lateral sulcus begins medially at
the anterior perforated substance and ends laterally on the lateral
surface by dividing into 3 rami, these rami are anterior, ascending &
posterior ramus.
Both the anterior and ascending rami cuts into the inferior frontal
gyrus and are related to the motor speech area of the inferior frontal
gyrus.
Insula: is a small triangular area buried at the bottom of the lateral
sulcus, the edges of the lateral sulcus form the opercula of the insula.
The apex of the insula is called the limen insulae and the whole area
of the insula is surrounded by a circular sulcus.
3- Parieto-occipital sulcus which separates the occipital lobe from the
parietal lobe.
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The frontal lobe is subdivided into 4 gyri by 3 sulci (precentral, superior &
inferior frontal sulci) and the gyri are pre-central gyrus, superior, middle &
inferior frontal gyri.
The pre-central gyrus (area 4) is the main somato-motor area and is rich in
giant pyramidal cellsof Betz which give rise to part of the pyramidal fibers
(cortico-spinal tract).
This area is related to the frontal branch of the middle meningeal artery. The
body is represented in this gyrus upside-down as follows: lower limb and
perineum, trunk, upper limb, head and neck (from above downwards).
The other gyri are the superior, middle, and inferior frontal gyri. The inferior
frontal gyrus is cut by the anterior and ascending rami of the lateral sulcus
and contains the motor speech area of Broca (areas 44 and 45) which
controls the movements of larynx and tongue musculatures during speech.
Just in front of the pre-central gyrus is an area passing through the frontal
gyri known as pre- motor area (area 6) and is concerned with extrapyramidal
functions.
Frontal eye field (area 8):lies in the posterior part of the middle frontal
gyrus for conjucate movements of the eye.
Pre-frontal area: is the most anterior part of the frontal lobe and is
concerned with emotion, behavior and represents the personality buildup of
the person.
Lunate sulcus: within the occipital lobe, the area between it and occipital
pole is the primary visual area (17) which receives fibers of the optic
radiation coming from lateral geniculate body.
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Sulci and gyri on the lateral surface of the temporal lobe are superior and
inferior temporal sulci with 3 gyri (superior, middle, and inferior) temporal
gyri. On the upper surface of the superior temporal gyrus is the primary
auditory area is located, its number is area (41 and 42) which receives the
auditory radiation from medial geniculate body.
On the lateral surface of the parietal lobe we can see post central sulcus and
intraparietal sulci creating 3 gyri as post central gyrus, superior and inferior
parietal lobules.
The post central gyrus encloses between the central and post central sulci, is
rich with granular cells, its number as 312 and its function as somato-
sensory area.
We can see also on the lateral surface of the parietal lobe 2 very small gyri
known as angular and supramarginal gyri.
Sulci and Gyri on medial surface
There are 4 main sulci on the medial surface, these are: callosal, cingulate,
calcarine and parieto-occipital sulci.
1. Callosal sulcus is seen on the superior surface of the corpus callosum,
it separates corpus callosum from the cingulate gyrus and runs on it
the callosal branch of the anterior cerebral artery.
2. Cingulate Sulcus, runs parallel to and above the callosal sulcus,
enclosing between both these sulci the cingulate gyrus and within the
substance of the gyrus (within its white mater) is a kind of associated
fibers known as the cingulum .
Just opposite the splenium of corpus callosum, the cingulate sulcus
ends by turning upwards behind the upper end of the central sulcus
lining the paracentral lobule from behind, while opposite the middle
part of corpus callosum, the cingulate sulcus gives off an ascending
branch which limits the paracentral lobule from infront.
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The paracentral lobule is a somato motor and somato sensory center
for the leg and half of the periuneum and is supplied by the calloso-
marginal branch of the anterior cerebral artery.
The cingulate gyrus curves behind the splenium of corpus callosum to
join the para-hippocampal gyrus by a narrow band of cortex called the
isthmus.
The cingulate and parahippocampalgyri with the isthmus form a C-
shaped mass of grey mater called limbie lobe.
3. Calcarine sulcus: starts just below the splenium of corpus callosum
and runs backward as far as the occipital pole parieto-occipital sulcus
curves on the lateral surface of the hemisphere for a short distance.
The area encloses between calcarine and parieto-occipital sulci are a
Y-shaped structure called cuneus related to primary visual area.
The calcarine sulcus lodges the posterior cerebral artery, it also makes
a bulge in the posterior horn of the lateral ventricle known as calcar
avis.
The Lingual gyrus: is just below and parallel to the calcarine sulcus,
between it and collateral sulcus is continous anteriorly
with
parahippocampalgyrus.
On the medial surface of the temporal lobe we can see:
a. Collateral sulcus above this sulcus is the parahippocampalgyrus which
terminates anteriorly into the uncus which is limited laterally by a
small sulcus called the rhinal sulcus.
b. Below the collateral sulcus there is another sulcus which extends into
part of the occipital lobe and known as occipito-temporal sulcus.
These above this sulcus and encloses between the collateral and the
occipito-temporal sulci is the medial occipito-temporal gyrusand
below the occipito-temporal sulcus is the lateral occipito-temporal
gyrus.
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c. Enclosed between the posterior end of collateral sulcus and calcarine
sulcus is the lingual gyrus which is related to visual function.
d. Just in front of the anterior end of calcarine sulcus is the isthmus
which connects the cingulate gyrus with the parahippocampalgyrus
forming together c-shaped connection known as limbic lobe.
The white matter of cerebrum lies deep to the cerebral cortex and consists of
nerve fibers which connects the various part of the cerebral cortex together
as well as with the lower centers as with the brain stem, cerebellum and
spinal cord. They include 3 kinds of fibers:
1- Association fibers includes:
a. Short associated fibers connecting neighboring gyri or parts of
the same gyrus together.
b. Long associated fibers connecting one pole with another pole
within the same hemisphere. They are grouped in bundles, as
follows:
Cingulum passes within the cingulate gyrus and reaches the
parahippocampal and isthmus and to end into the uncus.
Superior longitudinal bundle, it begins in the frontal pole,
passes backward above the insula and curves behind it to
terminate into the temporal pole. It runs on the superolateral
surface of the cerebral hemisphere and is separated from the
cingulum by the corona radiate of the projecting fibers.
Inferior longitudinal bundle close to the inferior surfaces of
occipital and temporal lobes extends between the 2 poles.
Uncinate fasciculus extends from the orbital surface of frontal
lobe to temporal pole.
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2- Commissural fibers:
These fibers cross the midline and connect essentially the
corresponding areas of the 2 cerebral hemispheres together includes:
Anterior commissure, in the upper part of lamina terminals and
connect the 2 temporal lobes together.
Posterior commissure, lies in the lower lamina of the stalk of the
pineal body and guards the entrance to cerebral aqueduct.
Habenular commissure, lies in the upper lamina of the pineal stalk
and connects the habenular nuclei (in the habenular trigon on the
medial surface of pulvinar) of both sides together.
Formix (hippocampal commissure). It crosses the mid line between
the 2 crura of the formix. It connects the hippocampus of the 2
hemispheres.
Corpus callosum: is the largest commissure, connects the 2
hemispheres together. In a sagittal section it appears as an arched
structure situated in the central area of the medial surface. It consists
of 3 parts:
1- Genu, is the anteriorend if the corpus collosum. Its fibers extend
forwards towards the frontal poles of the 2 hemispheres forming
the forceps minor. Is connected to the lamina terminal is by the
rostrum.
2- Body (trunk) connects mainly the 2 parietal lobe and to a lesser
extent the 2 temporal lobes. Is closely related to the lateral
ventricle, its upper surface forms the floor of the upper
longitudinal cerebral fissure and is related to :
a- Lower border of flax cerebri and the inferior sagittal venous
sinus.
b- Anterior cerebral artery.
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3- Splenium: is the expanded posterior and the thickest part, it hides
the dorsal surface of the thalamus, pineal body and superior
colliculus of the mid-brain.
The fibers of the splenium pass backward toward the 2 occipital
poles to form the forceps major, these forceps major fibers indents
the medial wall of the posterior horn of the lateral ventricle
forming what is called the bulb of posterior horn.
Note: Some fibers of the radiated fibers form the body of the corpus
callosum packed together forming what is called the tapetum.
3- Projecting fibers connects white matter of cerebrum with that of the
spinal cord, it radiates toward cerebral surface as corona radiate,
passes between basal ganglia as internal capsule, also seen on the
anterior surface of M.O as pyramid and then continue after
decussation as anterior and lateral corticospinal tracts.
The Fourth Ventricle
Is the cavity of the hind brain encloses between the dorsal surface pons-
upper medulla and the cerebellum. Continuous above with 3
rd
ventricle via
cerebral aqueduct and inferiorly leads to the central canal of the spinal cord
bounded by:
1- Floor (Anterior Wall) by the dorsal surface of the pons and upper half
of medulla oblongata.
2- Posterior wall (Roof) as follows:
a) Upper half by superior medullary stretches between the 2
superior cerebellar peduncles, the lingual and lateral lemniscus.
b) Lower half by inferior medullary velum stretches between the
two cerebellar peduncles.
3- Lateral boundary on each side by superior
cerebellar peduncles above and inferior
cerebellar peduncles below and on each side.