What is the primary function of the Spinal Accessory nerve?

The primary function of the Spinal Accessory nerve, also known as cranial nerve XI, is to control the movement of specific neck muscles, particularly the trapezius and sternocleidomastoid muscles. The trapezius muscle is responsible for shoulder elevation and rotation of the scapula, while the sternocleidomastoid muscle aids in head rotation and flexion of the neck. The effective functioning of these muscles is crucial for various movements of the head and shoulders, which are essential for daily activities and maintaining proper posture.

The other choices refer to functions associated with different cranial nerves. For instance, movement of the tongue is primarily managed by the hypoglossal nerve (cranial nerve XII). The down and inward movement of the eye is controlled by the oculomotor nerve (cranial nerve III), and balance and hearing are primarily responsibilities of the vestibulocochlear nerve (cranial nerve VIII). Understanding these associations helps to clarify the specific roles of the cranial nerves in relation to their anatomical and functional contributions to the body's nervous system.