Exercise 4: The Cerebellum

Exercise 4 The cerebellum Neuroanatomy The cerebellum is located in the posterior cranial fossa. The tentorium as a roof of posterior fossa separates the cerebellum from occipital lobe of cerebrum. The structures below the tentorium (brain stem and cerebellum) are refer as infratentorial. The major landmarks of the cerebellum are hemispheres, vermis, flocculus, nodule, tonsils, and peduncles. Cerebellar hemispheres are bilaterally symmetrical that are continues with the midline, the vermis. The hemispheres are divided into three lobes, as anterior, posterior and flocculonodular. Anterior lobe is located on the superior surface toward the midbrain and rostral to the primary fissure. The superior surface is flattened, and the superior vermis blends with the hemispheres while the inferior surface is convex. Posterior lobe is the largest lobe of the cerebellum and can be seen on both superior and inferior surfaces. Part of the lobe which is located at the superior surface is flattened and superior vermis lies in between (same as anterior lobe) while inferior part of the lobe is convex, and two deep sulci clearly separate the inferior vermis from the hemispheres. The transverse fissure (horizontal) is located at the margin between the superior and inferior surfaces. The primary fissure separates the anterior and posterior lobe on the superior surface. The posterolateral fissure is located between the posterior and flocculonodular lobes and on the inferior surface. Flocculonodular lobe is a small component that lies at the rostral edge of the inferior surface and is somewhat concealed by the posterior lobe. It extends lateral from the midline as the slender bend with an expanded end irregularly shaped mass on each side. The tonsils are the most anterior inferior part of the hemispheres. It lies close to medulla, tonsils are almost oval shaped structure near the flocculonodular lobe, above the foramen magnum. Exercise 4 The cerebellum Neuroanatomy The cerebellum is connected to brainstem by three pairs of peduncles. The superior cerebellar peduncles are connected to the mid brain and the superior medullary velum is the v-shaped internal between the superior peduncles forms the superior part of the roof of the 4th ventricle. The inferior cerebellar peduncles are connected to the medulla and forms inferior medullary velum by connecting the peduncles at the midline as remainder of the roof of the 4th ventricle. The superior and inferior medullary velums can be seen clearly on midsagittal section of the brain. Arterial supply, three pairs of arteries supply the cerebellum: Posterior Inferior Cerebellar Arteries (PICA) from the vertebral arteries supply the inferior vermis and inferior part of the hemispheres (close to tonsils). Anterior Inferior Cerebellar Arteries (AICA) is the most caudal branch of basilar artery supply the anterolateral aspect of the undersurface of the hemispheres. Superior cerebellar arteries from the basilar artery supply the superior surface. Histology of Cerebellar cortex Three layers are seen in the sections: 1- The molecular layer is the outer layer underlying the pia mater. Contains the dendrites of the purkinje cells, stellate cells and the basket cells. 2- The purkinje cell layer, consist of a single row of purkinje cells, lies between the molecular and granular cell layers. The cell body is flask-shaped with the neck ascending vertically toward the molecular layer. 3- The granular layer is the inner layer overlying the white mater. It contains granular cells with 3 to 5 dendrites and Golgi cells which are cell bodies typically found near the border of the purkinje cell layer. The arbor vitae cerebelli is the white mater in the region of the vermis produce a branching treelike in sagittal section.