Cerebellum: Anatomy, Functions, and Ataxia Diagnosis

Overview

The cerebellum ("little brain") sits in the posterior cranial fossa, dorsal to the pons and medulla. Despite containing more neurons than the rest of the brain combined, it does not initiate movement. Instead, it fine-tunes motor commands, coordinates balance, and contributes to motor learning and certain cognitive functions.

Gross Anatomy

Three Anatomical Lobes

1. Anterior lobe: Spinocerebellum; receives proprioceptive input from the body. Paleocerebellum.
2. Posterior lobe: Largest; cerebrocerebellum; involved in motor planning and coordination of skilled voluntary movements. Neocerebellum.
3. Flocculonodular lobe: Vestibulocerebellum; balance and eye movements. Archicerebellum.

Two Hemispheres and Vermis

The midline vermis controls truncal posture and gait. The lateral hemispheres coordinate ipsilateral limb movements.

Foliations and Arbor Vitae

The highly folded cerebellar cortex creates the "tree of life" (arbor vitae) appearance on sagittal section — branching white matter surrounded by cortex.

Three Functional Divisions

1. Vestibulocerebellum (flocculonodular lobe): Balance, eye movements (VOR)
2. Spinocerebellum (vermis + paravermis): Posture, gait, muscle tone
3. Cerebrocerebellum (lateral hemispheres): Motor planning, coordination of skilled movements, motor learning

Deep Cerebellar Nuclei (medial to lateral)

1. Fastigial: Vestibular nuclei — balance
2. Globose + Emboliform = Interposed: Red nucleus and thalamus — limb coordination
3. Dentate: Largest; thalamus and motor cortex — motor planning

Microscopic Anatomy: Three Cortical Layers

• Molecular layer (outer): Sparse cells, parallel fibers
• Purkinje cell layer (middle): Single row of giant Purkinje neurons with elaborate dendritic trees. Only output from cerebellar cortex (inhibitory, GABAergic to deep nuclei)
• Granular layer (inner): Densely packed granule cells; mossy fibers enter here

Input Pathways

• Mossy fibers: From spinocerebellar tracts, pontine nuclei, vestibular nuclei. Synapse on granule cells.