This accessory nerve has two components. The central portion of the nerve arises in the caudal part of the nucleus ambiguus in the medulla, close to the nuclei of IX, X and XII. It provides fibres for the vagus which may ultimately supply the intrinsic muscles of the larynx via the recurrent laryngeal nerve. The spinal portion of the accessory nerve arises from the upper five cervical segments, ascends within the dural sheath of the spinal cord through the foramen magnum, and then passes with the vagus for a short distance. It then heads dorsally, to supply the sternocleidomastoid muscle, and, with fibres from C3 and C4, trapezius.
The accessory nerve leaves the skull through the jugular foramen.
Last reviewed 01/2018