Which nerve innervates the upper trapezius muscle?

Which nerve innervates the upper trapezius muscle?

• A. Spinal accessory nerve (XI)
• B. Vagus nerve (X)
• C. Facial nerve (VII)
• D. Hypoglossal nerve (XII)

Answer: (A)

The upper trapezius is driven by the spinal accessory nerve. This nerve provides motor innervation to the trapezius (and the sternocleidomastoid), enabling actions like elevating the scapula and helping with arm elevation. Because of its superficial path in the posterior neck, it’s the nerve most often tested for shrug strength and is the classic source of trapezius weakness when damaged. The other nerves listed do not supply the trapezius: the vagus nerve handles autonomic and laryngeal/pharyngeal function, the facial nerve controls facial expression, and the hypoglossal nerve moves the tongue. A spinal accessory nerve injury would manifest as reduced ability to elevate the shoulder or shrug the shoulder.

The upper trapezius is driven by the spinal accessory nerve. This nerve provides motor innervation to the trapezius (and the sternocleidomastoid), enabling actions like elevating the scapula and helping with arm elevation. Because of its superficial path in the posterior neck, it’s the nerve most often tested for shrug strength and is the classic source of trapezius weakness when damaged. The other nerves listed do not supply the trapezius: the vagus nerve handles autonomic and laryngeal/pharyngeal function, the facial nerve controls facial expression, and the hypoglossal nerve moves the tongue. A spinal accessory nerve injury would manifest as reduced ability to elevate the shoulder or shrug the shoulder.