Final answer:
The accessory nerve innervates the sternocleidomastoid and trapezius muscles, not the teres minor and deltoid muscles. The sternocleidomastoid muscles assist in head flexion and rotation, while the trapezius contributes to head extension and shoulder elevation.
Step-by-step explanation:
The accessory nerve, also known as the spinal accessory nerve, does not serve the teres minor and deltoid muscles; it innervates the sternocleidomastoid and trapezius muscles. These muscles are significant in movements of the head, neck, and shoulders. The accessory nerve allows for head flexion and extension, lateral flexion, and shoulder movements such as shrugging. When the sternocleidomastoids contract together, they contribute to flexing the head forward, and when they contract individually, they cause rotation of the head to the opposite side. The trapezius muscle acts as an antagonist to these movements by causing extension and hyperextension of the neck. Neither the teres minor nor the deltoid muscle is innervated by the accessory nerve; the deltoid muscle, for instance, is primarily innervated by the axillary nerve, which allows for the abduction of the arm.