Which muscles are innervated by the accessory nerve (CN XI)?

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Multiple Choice

Which muscles are innervated by the accessory nerve (CN XI)?

The accessory nerve (CN XI) is a motor nerve that specifically innervates two neck muscles: the sternocleidomastoid and the trapezius. These muscles enable head turning and shoulder shrugging, key actions that reflect CN XI’s role. The deltoid and teres minor are supplied by the axillary nerve, not CN XI. The masseter and temporalis are innervated by the trigeminal motor branch, and the mylohyoid and anterior belly of the digastric are supplied by the nerve to mylohyoid (a branch of V3). Because the combination of sternocleidomastoid and trapezius innervation is unique to CN XI, this option best matches the nerve’s actual targets.

The accessory nerve (CN XI) is a motor nerve that specifically innervates two neck muscles: the sternocleidomastoid and the trapezius. These muscles enable head turning and shoulder shrugging, key actions that reflect CN XI’s role. The deltoid and teres minor are supplied by the axillary nerve, not CN XI. The masseter and temporalis are innervated by the trigeminal motor branch, and the mylohyoid and anterior belly of the digastric are supplied by the nerve to mylohyoid (a branch of V3). Because the combination of sternocleidomastoid and trapezius innervation is unique to CN XI, this option best matches the nerve’s actual targets.

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