Accessory nerve

The accessory nerve (or "Spinal accessory nerve") is the eleventh of twelve cranial nerves. It leaves the cranium through the jugular foramen along with the glossopharyngeal nerve (IX) and vagus nerve (X). It innervates the sternocleidomastoid muscle (sternomastoid) and trapezius muscle on the ipsilateral side.

There are two parts to the accessory nerve:
 * A spinal part, that innervates the muscles around the neck.
 * A cranial part, that splits off, and quickly combines with the vagus nerve. The cranial part of nerve XI can be thought of doing the exact same things as the vagus.

Testing the accessory nerve
Getting a person to shrug their shoulders while you push down tests trapezius. When a person turns their head, especially against force, sternocleidomastoid should be prominent.