Posterior Perspective of the Accessory Nerve (cn Xi)

Description

Arising from the posterolateral medulla as a cranial root and from upper cervical spinal cord segments as a spinal root, the accessory nerve (CN XI) is traced as it ascends through the foramen magnum and exits the skull via the jugular foramen. From this posterior perspective, the nerve courses inferiorly and laterally across the upper cervical region toward the shoulder girdle, in close relationship to the cervical vertebrae and the posterior skull base. The scapulae and proximal humeri frame the target territory, with CN XI heading toward the sternocleidomastoid more anteriorly and then crossing the posterior triangle to reach trapezius along its deep surface. A clean posterior map. This view matters because the spinal accessory nerve is both superficial and vulnerable in the posterior cervical triangle, where it can be injured during lymph node biopsy, neck dissection, or placement of surgical drains. Denervation of trapezius produces characteristic shoulder droop, lateral scapular winging, and loss of overhead abduction due to impaired upward rotation, findings that are easy to correlate when you can follow the nerve from its cervical roots toward the scapular spine. The relationship to upper cervical spinal nerves also supports teaching the difference between motor CN XI supply and cutaneous sensation from the cervical plexus. Use this artwork in head and neck anatomy labs, neurology teaching decks on lower cranial nerve lesions, and surgical texts illustrating posterior triangle risk zones during oncologic neck dissection. It also supports patient education materials on postoperative shoulder dysfunction after iatrogenic CN XI palsy. Anatomical accuracy verified by SciePro's Medical Advisory Board.