Which cranial nerve is the only one that emerges from the dorsal aspect of the brainstem and decussates completely within itself before exiting?

• A Oculomotor nerve
• B Trochlear nerve ✓
• C Abducens nerve
• D Hypoglossal nerve

Explanation

The trochlear nerve arises from the trochlear nucleus at the level of the inferior colliculus, decussates completely in the superior medullary velum, and emerges from the dorsal surface of the midbrain just below the inferior colliculus. It therefore supplies the contralateral superior oblique muscle. The oculomotor and abducens nerves emerge ventrally from the brainstem, and the hypoglossal nerve emerges ventrolaterally from the medulla as rootlets between the olive and the pyramid.

Reference: Gray's Anatomy, 42nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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