Accessory nerve

The accessory nerve is a cranial nerve that controls the sternocleidomastoid and trapezius muscles. As part of it was formerly believed to originate in the brain, it is considered the eleventh of twelve cranial nerves, or simply cranial nerve XI.

Traditional descriptions of the accessory nerve divide it into two parts: a spinal part and a cranial part. However, because the cranial component rapidly joins the vagus nerve, becoming an integral part of said nerve, modern descriptions often consider the cranial component to be part of the vagus nerve and not part of the accessory nerve proper. For this reason, in contemporary discussions of the accessory nerve, the common practice is to dismiss the cranial part altogether, referring to the accessory nerve specifically as the spinal accessory nerve.