Cerebellar Anatomy and Physiology

Learning objectives

Anatomy of Cerebellum and its connections Clinical presentation of cerebellar strokes Management of cerebellar strokes

Introduction

• The cerebellum contains as many neurons as the entire cerebrum. Its primary role is the coordinating motor function with other parts of the brain.
• It is composed of a core of white matter surrounded by grey matter.
• The cerebellum also consists of a cortex covered in grey matter folded into folia with deep fissures.
• Anatomically it is closely related to the IVth ventricle and contains 4 deep nuclei called the dentate, emboliform, globose and fastigial.
• The cerebellum receives sensory input as well as input from the motor and premotor cortex and returns feedback to these same centres.
• As such the cerebellar hemispheres deal with ipsilateral movement and function. Cerebellar hemispheres communicate via inferior, middle and superior cerebellar peduncles.
• Inferiorly lie the cerebellar tonsils which are important in Arnold-Chiari malformations.
• The cerebellum is separated from the pons by the fourth ventricle.
• Histologically the important functional cell is the Purkinje cell which lies between the molecular and deep granular layer of cells. The purkinje cells communicate with the deep cerebellar nuclei.
• The cerebellum is composed of a midline vermis and two lateral cerebellar hemispheres.
• It is composed of anterior and posterior lobes and flocculomodular lobe.
• The vermis is concerned with midline and truncal position and receives input from the spinal cord. Dysfunction is noted by postural instability and gait ataxia.
• Processing occurs in the cerebellar hemisphere and output is via the superior cerebellar peduncle which decussates in the midbrain and whose fibres pass to the motor nuclei of the thalamus and from there back to the motor and premotor cortex.

Cerebellar peduncles

• The cerebellum attaches to the posterior aspect of the brainstem by 3 large tracts, the superior, middle and inferior cerebellar peduncles. Do not confuse these with the cerebral peduncle.
• Superior cerebellar peduncle (brachium conjunctivum) contains efferent fibres from the cerebellum to other centres.
• Middle cerebellar peduncle (brachium pontis) has afferent fibres from the cerebral cortex. The cerebellar hemispheres receive input from the contralateral motor and premotor cortices by fibres which have decussated in the pons and enter the cerebellum via the middle cerebellar peduncle. The middle peduncle brings input from pontine nuclei.
• Inferior cerebellar peduncle receives input from the spinal cord.

Cerebellar Anatomy:The cerebellum is composed of three lobes

• Anterior lobe (lobules I-V according to the revised Larsell classification): anterior lobe is separated from the posterior lobe by the primary fissure, which is easily identified in the axial and midsagittal plane as the deepest and thickest fissure in the superior part of the vermis
• Posterior lobe (lobules VI-IX): There are two prominent fissures within the posterior lobe of the cerebellum; the posterior superior fissure and the great horizontal fissure. The posterior superior fissure runs parallel and posterior to the primary fissure in the superior surface of the cerebellum. The great horizontal fissure runs together with the posterior superior fissure in the midline. More laterally, it slopes inferiorly in the posterior surface of the cerebellum. Lobule VI is easily recognized as the area in between the primary fissure and the posterior superior fissure
• Flocculonodular lobe (lobule X) : composed of the nodulus in the midline and the flocculus in the cerebellar hemispheres.

Vascular Supply

• Superior Cerebellar Artery: The SCA territory is in the superior and tentorial surface of the cerebellum. It comes off the basilar artery.
• Anterior Inferior Cerebellar Artery : Comes of the basilar artery.
• Posterior Inferior Cerebellar Artery: comes of the ipsilateral vertebral artery and supplies lateral medulla and inferior surface of the cerebellum. The PICA and AICA are in balance, if one is smaller the other larger and vice versa.
• Venous drainage by the superior and inferior cerebellar veins. They drain into the superior petrosal, transverse and straight dural venous sinuses.

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