The Trapezius shares its innervation (CN XI - spinal accessory) with the sternocleidomastoid. Additionally, the bulbar portion of CN XI distributes with the recurrent laryngeal branch of CN X (vagus).

Myopathy or neuropathy associated with the trapezius results in an inability to shrug the shoulders. The extent of damage to CN XI can be determined by asking the patient to shrug the shoulders, turn the head to the opposite side against resistance, and evaluating voice production for hoarseness.