Cranial Nerve XI, also known as the accessory nerve, is responsible for controlling certain muscles in the neck and shoulders. It has two main parts: the spinal part, which originates from the spinal cord, and the cranial part, which arises from the brainstem. This nerve primarily innervates the sternocleidomastoid and trapezius muscles, enabling movements such as head rotation and shoulder elevation. Damage to Cranial Nerve XI can lead to weakness or paralysis in these muscles, resulting in difficulty turning the head or lifting the shoulders. Clinical tests often assess the function of this nerve by evaluating the strength of neck and shoulder movements.