What is the function of CN XI, known as the spinal accessory nerve?

• A. Sensory nerve for taste
• B. Motor control of shoulder and neck muscles
• C. Vision and eye movement
• D. Smell detection

Answer: (B)

The spinal accessory nerve, also known as CN XI, primarily serves a motor function. Its main role involves the innervation of certain muscles in the neck and shoulders, specifically the sternocleidomastoid and trapezius muscles. This control allows for movements such as turning the head and lifting the shoulders, which are critical for various physical activities and maintaining posture.

Understanding this function clarifies the importance of the spinal accessory nerve in coordinating neck and shoulder mobility. The other options pertain to different cranial nerves: sensory functions like taste and smell are associated with separate nerves, while vision and eye movement are managed by distinct cranial nerves responsible for ocular functions. Thus, the correct answer highlights the unique role of the spinal accessory nerve in motor control rather than sensory perception or eye movement.