The accessory nerve is a cranial nerve that controls the movement of certain neck muscles. It is coiled in appearance. It is divided into spinal and cranial divisions, but its cranial part is often disregarded.

The spinal accessory nerve provides motor function to the sternocleidomastoid muscle, which extends the neck and the trapezius, as well as the upper back and shoulder. Dysfunction of the spinal accessory nerve can negatively affect the shoulder’s performance.

Accessory nerve palsy is one complication that most often occurs after surgery has been performed on the neck’s posterior triangle, a triangle-shaped area that lies between the sternocleidomastoid and trapezius on each side of the neck. Additionally, there are three types of accessory nerve schwannoma tumors that occur in some people: intracisternal, spinal canal, and intrajugular; they can be removed with surgery from beneath the base of the skull. Schwannoma tumors are tumors that grow in the tissue that covers nerves, the nerve sheath.