Cerebellar Cortex Layers

Expansion

Three layers, surface inwards:

1. Molecular layer - few cells, mainly dendrites and parallel fibres. Contains stellate and basket cells
2. Purkinje cell layer - a single layer of large flask shaped neurones with an extensive flat dendritic tree
3. Granular layer - densely packed granule cells, the most numerous neurones in the entire brain

“The Purkinje cell is the only output, and it is inhibitory.” Purkinje cells project to the deep cerebellar nuclei using GABA, so the cerebellar cortex modulates by inhibition.

Two inputs

• Mossy fibres - from the spinal cord and pons, synapsing on granule cells, whose axons become parallel fibres in the molecular layer, contacting many Purkinje cells
• Climbing fibres - from the inferior olive, each wrapping a single Purkinje cell and producing a powerful response, thought to signal error for motor learning

Clinical correlation follows the anatomy: midline (vermis) lesions cause truncal ataxia and gait instability; lateral hemisphere lesions cause limb ataxia, intention tremor and dysdiadochokinesia ipsilaterally, because cerebellar connections are doubly crossed.

Purkinje cells are highly vulnerable to hypoxia, alcohol and paraneoplastic antibodies, which is why chronic alcohol causes vermian degeneration and a broad based gait.