What is the primary function of the Accessory nerve?

The Accessory nerve, also known as cranial nerve XI, primarily functions in providing motor innervation to certain neck muscles. Specifically, it innervates the sternocleidomastoid and trapezius muscles, which are crucial for movements such as turning the head and elevating the shoulders. This nerve originates from the upper spinal cord and enters the skull briefly before exiting to reach its target muscles, highlighting its role in facilitating head movement and shoulder elevation. This motor function is critical for activities involving neck rotation and shoulder shrugging, making the accessory nerve essential for various movements and posture maintenance.

In contrast, the other options relate to functions that are not associated with the Accessory nerve. Vision control pertains to the optic nerve, balance and coordination are typically handled by the vestibulocochlear nerve and the cerebellum, and hearing and balance are functions managed by the vestibulocochlear nerve as well. Thus, option C accurately reflects the primary role of the Accessory nerve in motor control of neck muscles.