Which cranial nerve is primarily responsible for motor function in the trapezius muscle?

The accessory nerve, or cranial nerve XI, is primarily responsible for the motor function of the trapezius muscle. This nerve originates from the upper cervical spinal cord, rather than the brainstem, and it supplies motor innervation to the sternocleidomastoid and trapezius muscles. The trapezius muscle is crucial for various movements of the shoulders and neck, including shrugging and head rotation.

The accessory nerve's role is specifically focused on the elevation of the scapula and movements that tilt the head backward, highlighting its importance in the overall function of shoulder and neck stability. Understanding the function of cranial nerves in muscle innervation is important for recognizing potential neurological issues or muscle-related disorders in clinical practice.