Cerebellum: Anatomical Regions

The cerebellum is divided into two hemispheres by a thin median structure called the vermis. These hemispheres are further partitioned into the anterior and posterior lobes, separated by the primary fissure. Inferiorly, the flocculonodular lobe is separated from the posterior lobe by the posterolateral fissure. Each region has distinct functional roles in motor control and coordination.

The cerebellar cortex contains gray matter arranged in parallel folds called folia. It includes three layers: the molecular layer with stellate and basket cells, the Purkinje cell layer with large neurons that relay motor impulses, and the granular layer densely packed with excitatory granule cells. Below the folia lies white matter known as the arbor vitae.

The cerebellum connects to the brainstem through three pairs of cerebellar peduncles. The superior peduncles connect the cerebellum with the midbrain, diencephalon, and cerebrum. The middle peduncles carry motor impulses from the pons to the cerebellum. The inferior peduncles pass sensory information from the medulla to the cerebellum.

Purkinje cells are heavily branched neurons located in the cerebellar cortex that relay motor impulses. These large, flask-shaped neurons have elaborate branching dendritic trees that receive inputs from two main sources: parallel fibers from granule cells and climbing fibers from the inferior olivary nucleus of the brainstem.

The cerebellum is positioned inferior to the posterior part of the cerebrum in the posterior cranial fossa. It plays a significant role in motor control, coordination, and proprioception. The vermis coordinates axial and proximal limb musculature, while the flocculonodular lobe maintains balance and equilibrium.

Deep cerebellar nuclei—the fastigial, globose, emboliform, and dentate nuclei—are embedded within the white matter of the arbor vitae. These nuclei receive input from the cerebellar cortex and send output to various brainstem nuclei and the thalamus, facilitating communication between the cerebellum and other brain regions.

Granule cells are small, excitatory neurons densely packed in the granular layer of the cerebellar cortex. They receive input from mossy fibers and give rise to parallel fibers that synapse onto Purkinje cells. This arrangement allows granule cells to relay and process motor and sensory information throughout the cerebellum.