Final answer:
The lateral branch of C2 does not directly innervate the sternocleidomastoid and trapezius muscles, which are controlled by the spinal accessory nerve.
Step-by-step explanation:
The lateral branch of C2, which is the second cervical spinal nerve, does not innervate the muscles controlled by the accessory nerve directly. Instead, the accessory nerve innervates the sternocleidomastoid and trapezius muscles. The sternocleidomastoids are involved in head flexion and rotation to the opposite side, while the trapezius muscles contribute to extension and lateral flexion of the neck.
The spinal accessory nerve works along with cervical spinal nerves, and testing its function involves examining movements like neck flexion, extension, and shoulder elevation through muscle strength tests.