Which statement about the trochlear nerve (CN IV) is correct?

• A Its nucleus lies in the medulla below the hypoglossal nucleus
• B It supplies four extraocular muscles including the levator palpebrae superioris
• C It is the only cranial nerve that emerges from the dorsal aspect of the brainstem and decussates completely ✓
• D It exits the skull through the superior orbital fissure outside the common tendinous ring

Explanation

CN IV is unique: its fibers cross completely in the anterior medullary velum and it is the only cranial nerve to emerge dorsally, from the dorsal midbrain just below the inferior colliculus. It does supply the superior orbital fissure, but through the common tendinous ring along with CN III and CN VI, so option D is false. Its nucleus lies in the caudal midbrain at the level of the inferior colliculus.

Reference: Snell's Clinical Neuroanatomy, 8th ed.

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