Which nerve in the medulla is responsible for head turning and shoulder shrugging?

• A. Oculomotor (III)
• B. Spinal Accessory (XI)
• C. Trigeminal (V)
• D. Glossopharyngeal (IX)

Answer: (B)

Head turning and shoulder shrugging are produced by the sternocleidomastoid and trapezius muscles, which are innervated by the spinal accessory nerve. This nerve carries motor fibers to those two muscles, enabling the neck to rotate the head and the shoulders to elevate. The motor neurons for this nerve reside in the upper spinal cord (the spinal accessory nucleus); the fibers travel upward, pass through the medulla area, and then exit the skull to reach their targets. Other nerves listed have different roles—one governs most eye movements, another controls muscles of mastication and facial sensation, and another aids swallowing and throat sensation—so they don’t explain head rotation and shoulder shrugging as directly.