Which nerve, when affected during a neck dissection, can impact the trapezius muscle?

The spinal accessory nerve is crucial for the functionality of the trapezius muscle, which is responsible for movements such as shrugging the shoulders and elevating the scapula. During a neck dissection, if this nerve is inadvertently damaged or affected, it can lead to weakness or paralysis of the trapezius muscle, resulting in difficulty with shoulder elevation and abnormal shoulder posture.

The spinal accessory nerve, also known as cranial nerve XI, innervates the sternocleidomastoid and trapezius muscles. Its preservation during surgical procedures is essential for maintaining normal shoulder function.

In this context, the other nerves mentioned do not have a direct role in innervating the trapezius muscle. The vagus nerve primarily controls autonomic functions and does not serve the trapezius. The hypoglossal nerve is involved in tongue movement and also does not affect the trapezius. The facial nerve primarily innervates muscles of facial expression, with no connection to the trapezius muscle. Thus, the spinal accessory nerve’s specific role in trapezius muscle innervation makes it the correct answer for this question.