Internal Structure: Gray and White Matter
Two distinct types of tissue are clearly visible on a section of the cerebellum. The surface is covered by gray matter, forming the cerebellar cortex (cortex cerebelli). The cortex contains three cytoarchitectural layers (from the surface inward):
- Molecular layer (stratum moleculare);
- Purkinje cell layer (stratum neuronorum piriformium);
- Granular layer (stratum granulosum).
Beneath the cortex lies the white matter, which forms the medullary body of the cerebellum (corpus medullare cerebelli). On sagittal sections, branches of white matter extending into the folia create a characteristic branching pattern known as the arbor vitae (arbor vitae cerebelli). Embedded within this white matter are clusters of gray matter—the deep cerebellar nuclei (nuclei cerebelli).
Deep Cerebellar Nuclei
Four paired nuclei are embedded within the white matter of each hemisphere and the vermis. They serve as the primary output centers through which the cerebellum communicates with other brain regions.
- Fastigial nucleus (nucleus fastigii) — located most medially, within the white matter of the vermis near the roof of the fourth ventricle. It belongs to the oldest phylogenetic structure (archaeocerebellum) and projects fibers to the vestibular nuclei and reticular formation.
- Globose nucleus (nucleus globosus) — situated in the hemisphere, medial to the dentate nucleus. It belongs to the palaeocerebellum and connects to the red nucleus via the superior peduncle.
- Emboliform nucleus (nucleus emboliformis) — lies parallel and slightly medial to the dentate nucleus. Like the globose nucleus, it is part of the palaeocerebellum and has efferent connections to the red nucleus.
- Dentate nucleus (nucleus dentatus) — the largest and most lateral nucleus, located in the mediolateral regions of the hemisphere. It belongs to the neocerebellum and forms the dentatothalamic tract (tractus dentatothalamicus) projecting to the thalamus.
Cerebellar Peduncles
The cerebellum is firmly anchored to the brainstem by three pairs of peduncles (pedunculi cerebellares), through which all afferent and efferent pathways pass:
- Inferior cerebellar peduncles (pedunculi cerebellares caudales / inferiores) — connect the cerebellum to the medulla oblongata.
- Middle cerebellar peduncles (pedunculi cerebellares medii) — provide bidirectional communication with the pons.
- Superior cerebellar peduncles (pedunculi cerebellares rostrales / superiores) — project toward the midbrain.
Lobes and Phylogenetic Divisions
During evolution, the cerebellum developed unevenly; thus, it is divided into three phylogenetic regions that closely correlate with anatomical lobes.
Archaeocerebellum (archaeocerebellum) is represented by the flocculonodular lobe (lobus flocculonodularis), which includes the nodulus of the vermis (nodulus) and the flocculus of the hemispheres (flocculus). This part is separated by the posterolateral fissure (fissura dorsolateralis) and is responsible for vestibular connections.
Palaeocerebellum (palaeocerebellum) corresponds to the anterior lobe (lobus rostralis / anterior), excluding the lingula. It includes vermal structures such as the lingula, central lobule, and culmen, as well as the anterior part of the quadrangular lobule of the hemispheres. It is separated by the primary fissure (fissura prima) and receives spinocerebellar pathways.
Neocerebellum (neocerebellum) is the evolutionarily youngest part, represented by the posterior lobe (lobus caudalis / posterior). It occupies the space between the primary and posterolateral fissures. It includes the declive, pyramis, uvula of the vermis, and extensive regions of the hemispheres (posterior part of the quadrangular lobule, semilunar lobules, tonsil). The neocerebellum mediates complex cortico-ponto-cerebellar pathways.