Cranial nerve XI: The eleventh cranial nerve is the accessory nerve. The twelve cranial nerves, the accessory nerve included, emerge from or enter the skull (the cranium) as opposed to the spinal nerves which emerge from the vertebral column. The accessory is so-called because, although it arises in the brain, it receives an additional (accessory) root from the upper part of the spinal cord.
The accessory nerve supplies the sternocleidomastoid and trapezius muscles. The sternocleidomastoid muscle is in the front of the neck and turns the head. The trapezius muscle moves the scapula (the wingbone), turns the face to the opposite side, and helps pull the head back.
Damage to the accessory nerve can be isolated (confined to the accessory nerve) or it may also involve the ninth and tenth cranial nerves which exit through the same opening (foramen) from the skull . Accessory neuropathy (nerve disease) can sometimes occur and recur for unknown reasons. Most patients recover.