Which cerebellar peduncle is the largest, and what are its principal constituent fibres?

• A Superior peduncle, carrying dentatorubral and dentatothalamic fibres
• B Inferior peduncle, carrying spinocerebellar and olivocerebellar fibres
• C Middle peduncle, carrying pontocerebellar fibres from the contralateral pontine nuclei ✓
• D Middle peduncle, carrying vestibulocerebellar fibres from the ipsilateral vestibular nuclei

Explanation

The middle cerebellar peduncle is the largest of the three and consists almost entirely of transverse pontine fibres that cross from the contralateral pontine nuclei to reach the neocerebellar cortex, forming part of the cortico-ponto-cerebellar pathway. Option A describes the superior peduncle, which is the main output route, and option B describes the inferior peduncle. Vestibulocerebellar fibres travel mainly through the inferior peduncle, which eliminates D. This input-output arrangement explains why pontine lesions produce marked contralateral limb ataxia.

Reference: Gray's Anatomy, 42nd ed.

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