Hemisphere of cerebellum

The two large laterally situated hemispheres of cerebellum are separated from the midline vermis–on each side–by a paramedian fissure. A cut-section through the hemispheres of cerebellum, reveals an outer layer of cerebellar cortex, which envelopes a central core of white matter. Due to the presence of various transverse fissures in a mediolateral plane, the hemispheres of cerebellum and the vermis get divided into several lobes and lobules, with each lobule being further sub-divided into folia (or leaflets). These lobules have been labelled from I to X[H] by Larsell (H meaning hemisphere), which is homologous to the classic nomenclature and the classification proposed earlier by Bolk.

Anatomically, the cerebellum can be divided into three lobes. The anterior lobe–in front of the primary fissure–contains lobules I-V[H] of hemisphere of cerebellum (Larsell). These are labelled as Vicingulum lingulae, Ala of lobuli centralis and Anterior quadrangular lobules of hemisphere of cerebellum, as per the classic nomenclature system.

When it comes to the middle (or posterior) lobe, this region contains Larsell’s lobules VI-IX[H] of hemisphere of cerebellum. Lobule VI[H] (Larsell) correlates with ‘simplex lobule’ (Bolk’s classification) or with ‘posterior quadrangular lobule’ (classic nomenclature). Similarly, lobule VIIA[H] (Larsell) is the same as ‘ansiform lobule’ (Bolk) or the ‘superior and inferior semilunar lobules’ (as per the classic nomenclature). Next, lobules VIIB[H] and VIII[H] (Larsell) are the same as Bolk’s ‘paramedian lobule’ or the classic nomenclature’s ‘gracile and biventral lobules’, respectively. Lastly, lobules IX[H] (Larsell) coincide with Bolk’s ‘paraflocculus’ or with the ‘tonsil’ in the classical naming system.

In case of the flocculonodular lobe (or vestibulocerebellum), Larsell’s lobule X[H] of the hemisphere of cerebellum can be found here, behind the posterolateral fissure. Lobule X[H] has been labelled as the ‘flocculus’ both by Bolk and as per the classical paradigm. The flocculonodular lobe is linked with balance regulation.

The hemispheres of cerebellum receive information from the cerebrum (via corticopontocerebellar pathways) about the predicted or intended plan of the voluntary movement, that had been originally formulated in the cerebral cortex. This is matched with the ‘actual’ movement happening in real-time (this information comes from spinal cord via spinocerebellar pathways). Consequently, any mismatch between the intended plan and the actual movement could be corrected by the cerebellum, thus contributing to the precision, accuracy, planning and timing of movements.

A stroke in the hemisphere of cerebellum–including the paramedian region–could lead to motor incoordination, tremors and ataxia.