A patient with a small lacunar infarct in the basis pontis presents with ipsilateral limb ataxia out of proportion to weakness. The lesion involves the pontine relay nuclei that receive corticopontine fibres and give rise to transverse pontocerebellar fibres. Which nucleus is most directly responsible?
- A Superior olivary nucleus
- B Arcuate nucleus ✓
- C Pontine nuclei (nuclei pontis)
- D Mesencephalic nucleus of the trigeminal nerve
Correct answer: B. Arcuate nucleus
Explanation
The arcuate nucleus, located ventral to the pyramidal tract in the medulla and lower pons, is a precerebellar relay nucleus. It receives corticopontine fibres and sends arcuatocerebellar fibres via the inferior cerebellar peduncle to the cerebellum. Lesions here cause ipsilateral ataxia. Option C (nuclei pontis) also relays cortical input but sends fibres via the middle cerebellar peduncle; the arcuate nucleus is the medullary analogue and is the best answer for a basis pontis/medullary level lesion.
Reference: Gray's Anatomy, 42nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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