Which cranial nerve controls muscles in the neck and upper back?

• A. Hypoglossal (XII)
• B. Spinal Accessory (XI)
• C. Auditory (VIII)
• D. Glossopharyngeal (IX)

Answer: (B)

The cranial nerve responsible for controlling muscles in the neck and upper back is the Spinal Accessory nerve, also known as cranial nerve XI. This nerve primarily innervates two key muscles: the sternocleidomastoid and the trapezius. The sternocleidomastoid muscle plays a vital role in head rotation and flexion, while the trapezius muscle supports movements of the shoulders and neck, contributing to actions such as shrugging and extending the neck.

In contrast, the other cranial nerves listed do not have the same functions related to neck and upper back muscle control. For instance, the Hypoglossal nerve primarily controls muscles of the tongue and is involved in speech and swallowing. The Auditory nerve is responsible for hearing and balance, while the Glossopharyngeal nerve plays roles in taste and swallowing but does not innervate neck and upper back muscles. Thus, the Spinal Accessory nerve is uniquely suited for its role in muscle movement in those specific areas.