cerebellum

The cerebellum is a major structure at the posterior aspect of the brain, tucked under the occipital lobes and continuous with the brainstem. It accounts for a small proportion of brain mass but contains a large share of neurons. The organ consists of two lateral hemispheres connected by the midline vermis, with the flocculonodular lobe forming a distinct vestibulocerebellar region. Its cortex is highly foliated, lying above an internal white matter scaffold known as the arbor vitae, and it contains deep cerebellar nuclei (dentate, interposed, fastigial) that relay processed signals.

Afferent and efferent connections are organized around three cerebellar peduncles. The superior peduncle mainly carries efferent output from the cerebellum to brainstem and thalamus; the middle peduncle conveys afferent input from pontine nuclei; the inferior peduncle carries afferents from the spinal cord and lower brainstem and some efferents. The input network includes mossy fibers and climbing fibers that synapse on granule and Purkinje cells. Purkinje cells provide the sole cortical output, projecting inhibitory signals to the deep cerebellar nuclei, which in turn influence motor and premotor centers.

Functions of the cerebellum include the coordination of voluntary movement, precision, timing, balance, and posture. It contributes to motor learning and adaptation through error signaling and predictive modeling. The cerebellum also participates in certain cognitive and affective processes via cerebro-cerebellar circuits, with roles described in language, attention, working memory, and social cognition.

Clinical involvement ranges from ataxia and dysmetria to intention tremor and nystagmus following cerebellar injury or degeneration. Lesion location often dictates whether truncal (vermis) or limb (cerebellar hemispheres) coordination is predominantly affected.