Which nerve aids in the movement of the shoulder?

The correct answer is the spinal accessory nerve (CN XI), which is primarily responsible for the movement of shoulder muscles, particularly the trapezius and sternocleidomastoid. This nerve facilitates actions like shrugging the shoulders and turning the head, making it crucial for shoulder mobility. Its motor functions support both shoulder elevation and head rotation.

The other options, while they serve essential roles, do not specifically facilitate shoulder movement. The trigeminal nerve (CN V) is mainly involved in sensation and motor functions related to chewing. The facial nerve (CN VII) primarily controls the muscles of facial expression and does not influence shoulder movement. The vagus nerve (CN X) has a broader autonomic function focused on regulating internal organ functions, particularly in the thorax and abdomen, rather than contributing directly to shoulder mechanics.