Accessory Nerve (cn Xi), Posterior View

Description

Running superficially across the posterior neck, the spinal root of the accessory nerve (CN XI) ascends from the upper cervical spinal cord, then courses superolaterally toward the jugular foramen before turning inferiorly within the carotid sheath region to reach the sternocleidomastoid and trapezius. From a posterior angle, its cervical segment is shown in relation to the spinous processes of the upper thoracic vertebrae, the posterior ribs, and the scapulae, with the nerve tracking along the posterolateral neck toward the superior border and medial margin of the scapular girdle. Scapular landmarks such as the spine of the scapula and medial border help orient the distal trajectory toward trapezius. CN XI is superficial here. That surface anatomy matters clinically because the accessory nerve is vulnerable in posterior triangle procedures, most often during cervical lymph node biopsy or neck dissection, where injury produces trapezius weakness, lateral scapular winging, and impaired shoulder abduction above 90 degrees. A posterior depiction also helps clarify how a lesion distal to the sternocleidomastoid branch spares head rotation strength but compromises scapular elevation and upward rotation, a pattern that distinguishes CN XI palsy from long thoracic nerve injury. For surgeons, the nerve’s relationship to the posterior border of sternocleidomastoid and the trapezius anterior border is the operative problem. Use this artwork in gross anatomy lab manuals, head and neck surgery teaching decks, and neurology texts discussing lower cranial nerve examination and differential diagnosis of shoulder droop. It also fits patient education handouts for post neck surgery rehabilitation, where explaining trapezius denervation and scapular dyskinesis improves compliance with targeted physiotherapy. Anatomical accuracy verified by SciePro's Medical Advisory Board.