الاحد 1/12/2013 أ.د.عبد الجبار الحبيطي NEURO ANATOMY الاحد 1/12/2013 أ.د.عبد الجبار الحبيطي

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: -   Superolateral surface: - convex & lies in contact with the roof & side of the skull. Medial surface: - flat & lies in contact with the falx cerebri. 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 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 & parieto-occipital 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 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 & perineum, trunk, upper limb, head & neck (from above downwards).

The other gyri are the superior, middle & inferior orbital gyri 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 pre-motor 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 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 from the opposite half of the body except lower limb & perineum. It is supplied by middle cerebral artery & histologicaly rich in fine granular cells. 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.   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. 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.

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. Calcarine sulcus: - starts just below the splenium of corpus callosum & 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 & 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: - Collateral sulcus: - 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. 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.

3- Enclosed between the posterior end of collateral sulcus and calcarine sulcus is the lingual gyrus which is related to visual function. 4- 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: -   Association fibers includes:- Short associated fibers connecting neighboring gyri or parts of the same gyrus together. 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 via isthmus and to end into the uncus.

IV. 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). V. Inferior longitudinal bundle: - close to the inferior surfaces of occipital & temporal lobes extends between the 2 poles. VI.uncinate fasciculus: - extends from the orbital surface of frontal lobe to temporal pole.

2- Commissural fibers: - these fibers cross the midline and connects essentially corresponding parts of the 2 cerebral hemispheres together includes: - Anterior commissure: - in the upper part of lamina terminalis & connects 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 aquiduct. 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: 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.

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: - Lower border of falx cerebri and the inferior sagittal venous sinus. Anterior cerebral artery. Note: - some of the radiated fibers from the body of corpus callosum packed together forming what is called the Tapetum.

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.

3. 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).