Final answer:
Arm movement around the trunk is facilitated by axial muscles such as the pectoralis major and the latissimus dorsi, with the accessory nerve innervated sternocleidomastoid and trapezius muscles contributing to the stability of the shoulder and neck.
Step-by-step explanation:
Muscles Involved in Movement of the Arm Around the Trunk
The muscles involved in allowing movement of the arm around the trunk are complex and include both axial muscles,
which support the head, neck, and trunk, and scapular muscles, which attach to the shoulder girdle.
The primary axial muscles responsible for arm movements are the pectoralis major and the latissimus dorsi.
The pectoralis major is a large, fan-shaped muscle located on the anterior chest wall, while the latissimus dorsi is a broad, triangular muscle on the inferior back. Both muscles insert on the humerus bone of the arm and aid in its movement.
In addition, the accessory nerve innervates the sternocleidomastoid and trapezius muscles, which play a key role in moving the head and neck as well as stabilizing the shoulder and pectoral girdle.
This stabilization is essential for coordinated arm movements.
The sternocleidomastoid muscle, when contracted bilaterally, flexes the head forward and, when contracted unilaterally, causes rotation of the head to the opposite side.
The trapezius, on the other hand, acts as an antagonist to the sternocleidomastoid in head movement, and also contributes to the elevation of the scapula and clavicle, providing a stable base for arm movements.