Chapter 11 – Cerebellum

Publisher Summary This chapter explains the external gross anatomy of cerebellum. It explains the pattern of cerebellar lobules and folial pattern in cerebellum. The gross external anatomy of the murine cerebellum is typical of most mammals. The cerebellum consists of a series of median vermal lobules and prominent lateral extensions called hemispheres. The cerebellum forms the roof of the fourth ventricle; the superior medullary velum of the cerebellum forms the rostral part of the roof, and the caudal half of the cerebellum overhangs the ependymal roof and choroid plexus of the caudal half of the fourth ventricle. The cerebellum is attached to the brain stem by the three pairs of cerebellar peduncles. The peduncles are large fiber bundles, which carry the cerebellar efferent and afferent tracts. Three major afferent systems carry inputs to the cerebellar cortex. The climbing fibers, which originate from the contralateral inferior olivary nucleus of the medulla oblongata, synapse within the proximal dendrites of Purkinje cells. The second major afferent system, the mossy fibers, originates from many sites including the spinal cord, the brain stem and the pons. A single mossy fiber may influence hundreds of Purkinje cells, while relatively few Purkinje cells are stimulated by input from a single climbing fiber. The third major afferent system consists of fibers that originate from various regions of the brain including the locus coeruleus and raphe nucleus. These thin fibers are morphologically distinct from the climbing and mossy fibers and terminate within all layers of the cerebellar cortex and also within the cerebellar nuclei.