Download Neuro Anatomy Lec.7 أ.د.عبد الجبار الحبي طي The cerebrum consist

Neuro Anatomy
‫عبد اجلبار احلبيـطي‬.‫د‬.‫أ‬
Lec.7
The cerebrum consist 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: -
I- Superolateral surface: - convex & lies in contact with
the roof & side of the skull.
II- Medial surface: - flat & lies in contact with the falx
cerebri.
III- Inferior surface: - lies in contact with the floor of
anterior & middle cranial fossae & rests posteriorly
on the tentorium cerebelli, this surface include orbital
& tentorial parts.
Each hemisphere has 3 poles, frontal, temporal &
occipital poles. Each hemisphere is divided into 4 lobes
by 3 sulci, these lobes are frontal, parietal, temporal &
occipital lobes & the sulci are central, lateral & parietooccipital sulci. Each gyrus consists of a central core of
white matter covered by a layer of grey 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 & also possess different
functional areas, e.g. motor, general sensory, visual,
olfactory & auditory. The sulci vary in depth, some very
shallow, while others are very deep & may indents the
walls of the lateral ventricle as the calcarine & collateral
sulci.
Sulci & gyri on the lateral surface (outer surface) of the cerebral
hemisphere: -
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I-
Central sulcus passes on the Superolateral surface
downwards & forwards, to end a short distance
above the posterior ramus of the lateral sulcus, it
separate the frontal lobe from the parietal lobe &
thus it separates the motor area (in the pre central
gyrus) from the sensory area (in the post central
gyrus).
II- 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 & ends laterally
on the lateral surface by dividing into 3 rami, these
rami are anterior horizontal, ascending & posterior
rami. Both the anterior & ascending rami cuts into
the inferior frontal gyrus & are related to the motor
speech area of the inferior frontal gyrus (44 + 45).
Insula: - is a small triangular area buried at the bottom of
the lateral sulcus, the edge of the lateral sulcus forms the
opercula of the insula. The apex of the insula is called the
limen insulae & the whole area of the insula is surrounded
by a circular sulcus.
III- Parieto-occipital sulcus: - which separates the
occipital lobe from the parietal lobe.
 The frontal lobe: - is subdivided into 4 gyri by 3 sulci
(pre-central, superior & inferior frontal sulci) & the
gyri are pre-central gyrus, superior, middle & inferior
frontal gyri.
 the pre central gyrus (area 4) is the main
somatomotor area & is rich in giant pyramidal
cells of 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 &
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perineum, trunk, upper limb, head & neck (from
above downwards).
 The other gyri are the superior, middle & inferior
orbital gyri. The inferior orbital gyrus is cut by the
anterior & ascending rami of the lateral sulcus &
contains the motor speech area of the Broca
(areas 44 & 45) which controls the movements of
the larynx & tongue musculatures during speech.
 Just in front of the pre central gyrus is an area
passing through the frontal gyri, known as premotor area (area 6) & is concerned with extra
pyramidal functions.
 Frontal eye field (area 8): - lies in the posterior part
of the middle frontal gyrus for conjugate
movement of the eye.
 Pre frontal area: - is the most anterior part of the
frontal lobe & is concerned with emotion,
behavior & represents personality build up of
the person.
 Lunate sulcus: - within the occipital lobe, the area
between it & the occipital pole is the primary
visual area (17) which receives fibers of the
optic radiation coming from lateral geniculate
body.
Sulci & gyri on the lateral surface of the temporal lobe : - are superior
& inferior temporal sulci with 3 gyri (superior, middle &
inferior) temporal gyri. On the upper surface of the
superior temporal gyrus is the primary auditory area is
located, its number is areas 41 & 42 which receives the
auditory radiation from the medial geniculate body.
Sulci & gyri on the lateral surface of the parietal lobe: I- Post central sulcus in front & parallel to the central
sulcus. It encloses with the central sulcus what is
called the post-central gyrus (area 312) which is
primary sensory area receives sensory information
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from the opposite half of the body except lower limb &
perineum. It is supplied by middle cerebral artery &
histologicaly rich in fine granular cells.
II- Intraparietal sulcus, horizontal one & perpendicular to
post-central sulcus creating superior & inferior parietal
lobules.
The parietal lobe shows 2 additional small gyri as:  Supramarginal gyrus arching over the end of the
posterior ramus of the lateral sulcus.
 Angular gyrus: - it arches over the end of the
superior temporal sulcus.
Sulci & gyri on the medial surface: There are 4 main sulci on the medial surface these are: callosal, cingulate, calcarine & parieto-occipital sulci.
I-
The callosal sulcus is seen on the superior surface of
the corpus callosum; it separates corpus callosum
from the cingulate gyrus & run on it the callosal
branch of the anterior cerebral artery.
II-
Cingulate sulcus runs parallel to & above the callosal
sulcus, enclosing between both these sulci the
cingulate gyrus & 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 the corpus callosum,
the cingulate sulcus ends by turning upwards behind
the upper end of the central sulcus limiting 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 in front.
 The paracentral lobule is a somatomotor &
somatosensory center for the leg & half of the
perineum & is supplied by the calloso-marginal
branch of the anterior cerebral artery.
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 The cingulate gyrus curves behind the splenium of
corpus callosum to join the parahippocampal gyrus
by a narrow band of cortex called the isthmus. The
cingulate & parahippocampal gyri with the isthmus
form a C-shaped mass of gray matter called limbic
lobe.
III- Calcarine sulcus: - starts just below the splenium of
corpus callosum & runs backward as far as the
occipital pole.
IV- Parieto-occipital sulcus: - curves on the lateral
surface of the hemisphere for a short distance.
The area encloses between calcarine & parieto-occipital
sulci is 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 & parallel to the
calcarine sulcus, between it & collateral sulcus is
continuous anteriorly with parahippocampal gyrus.
On the medial surface of the temporal lobe we can see: I-
above this sulcus is the
parahippocampal gyrus which terminates anteriorly
into the uncus which is limited laterally by a small
sulcus called the rhinal sulcus.
Collateral
sulcus:
-
II- Below the collateral sulcus there is another sulcus
which extends into part of the occipital lobe and
known as occipito-temporal sulcus. thus above this
sulcus and encloses between the collateral & the
occipito-temporal sulci is the medial occipito-temporal
gyrus & below the occipito-temporal sulcus is the
lateral occipito-temporal gyrus.
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III- Enclosed between the posterior end of collateral
sulcus and calcarine sulcus is the lingual gyrus which
is related to visual function.
IV- Just in front of the anterior end of calcarine sulcus is
the isthmus which connects the cingulate gyrus with
the parahippocampal gyrus forming together c-shaped
connection known as limbic lobe.
The white matter of cerebrum lies deep to the cerebral cortex &
consists of nerve fibers which connect the various part of
the cerebral cortex together, as well as with the lower
centers as with the brain stem, cerebellum & spinal cord.
They include 3 kinds of fibers: I-
Association fibers includes:-
i- Short associated fibers connecting neighboring gyri
or parts of the same gyrus together.
ii- Long associated fibers connecting one pole with
another pole within the same hemisphere. They are
grouped in bundles, as follows:-
a- Cingulum: - passes within the cingulate gyrus
and reaches the parahippocampal via isthmus
and to end into the uncus.
b- 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
radiata (of the projecting fibers).
c- Inferior longitudinal bundle: - close to the
inferior surfaces of occipital & temporal lobes
extends between the 2 poles.
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d- uncinate fasciculus: - extends from the orbital
surface of frontal lobe to temporal pole.
Commissural fibers: - these fibers cross the midline
and connects essentially corresponding parts of the 2
cerebral hemispheres together includes: -
II-
i- Anterior commissure: - in the upper part of lamina
terminalis
together.
&
connects
the
2
temporal
lobes
ii- Posterior commissure: - lies in the lower lamina of
the stalk of the pineal body and guards the
entrance to cerebral aquiduct.
iii- 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.
iv- Fornix (Hippocampal commissure): - it crosses the
midline between the 2 crura of the fornix. it
connects the hippocampus of the 2 hemispheres.
v- Corpus callosum: - is the largest commissure,
connects the 2 hemispheres together. In a sagittal
section, it appears an arched structure situated in
the central area of the medial surface. it consists of
3 parts:
a- Genu: - is the anterior end of the corpus
callosum. its fibers extends forwards towards
the frontal poles of the 2 hemispheres forming
the forceps minor. Is connected to the lamina
terminalis by the rostrum.
b- Body (trunk): - connects mainly the 2 parietal
lobes & to a lesser extent the 2 temporal lobes.
Is closely related to the lateral ventricle, it’s
upper surface forms the floor of the median
longitudinal cerebral fissure and is related to: -
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1-
Lower border of falx cerebri and the inferior
sagittal venous sinus.
2-
Anterior cerebral artery.
Note: - some of the radiated fibers from the body
of corpus callosum packed together forming
what is called the Tapetum.
c- Splenium: - is the expanded posterior end and is
the thickest part, it hides the dorsal surface of
the thalamus, pineal body and superior colliculus
of the mid-brain. The fibers of 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.
III- Projecting fibers connects white matter of cerebrum
with that of the spinal cord, it radiates toward cerebral
surface as corona radiata, passes between basal ganglia
as the internal capsule (containing ascending &
descending tracts), and as pyramid on the surface of the
medulla oblongata (contain cortico-spinal tract).
The 4th ventricle: Is the cavity of the hind brain encloses between the dorsal
surface of pons, upper medulla & the cerebellum,
continuous above with 3rd ventricle via cerebral aquiduct &
inferiorly lead to the central canal of the spinal cord
bounded as: -
I-
Floor (Anterior wall): - by the dorsal surface of the
pons & upper half of the medulla oblongata.
II- posterior wall (roof) as follows: -
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i- Upper
1/2 by superior medullary velum
stretches between the 2 superior cerebellar
peduncles, the lingula & lateral lemniscus.
ii- Lower 1/2 by inferior medullary velum stretches
between the 2 inferior cerebellar peduncles.
III- Lateral boundary on each side by superior cerebellar
peduncle above & inferior cerebellar peduncle below
and on each side.
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