Final answer:
The accessory nerve innervates the sternocleidomastoid and trapezius muscles, which are involved in head movement and changing the position of the head. The muscles of the thorax, including the pectoralis major, facilitate breathing by changing the size of the thoracic cavity.
Step-by-step explanation:
Muscles Controlled by the Accessory Nerve:
The accessory nerve, also known as the spinal accessory nerve, innervates the sternocleidomastoid and trapezius muscles.
When both sternocleidomastoids contract, the head flexes forward; individually, they cause rotation to the opposite side.
The trapezius can act as an antagonist, causing extension and hyperextension of the neck. These two muscles are important for changing the position of the head and are also involved in elevating the scapula and clavicle through the trapezius.
Muscles of the Thorax
The muscles of the chest, such as the pectoralis major muscle, are important for facilitating breathing by changing the size of the thoracic cavity.
When you inhale, your chest rises because the cavity expands, and when you exhale, your chest falls because the thoracic cavity decreases in size.