Final answer:
The cranial nerve Accessory (CN XI) controls movement of the neck muscles sternocleidomastoid and trapezius.
Step-by-step explanation:
The cranial nerve identified as Accessory (CN XI) is responsible for controlling the movement of the sternocleidomastoid and trapezius muscles in the neck.
When both sternocleidomastoid muscles contract, the head flexes forward, while the individual contraction of these muscles causes rotation to the opposite side. The trapezius muscle can act as an antagonist, causing extension and hyperextension of the neck, and is involved in changing the position of the head.
The Accessory nerve receives motor input from the spinal cord and, along with cervical spinal nerves, contributes to the movement of the scapula and clavicle through the trapezius muscle.