Accessory Nerve

Description

Posterior left neck anatomy is rendered with the accessory nerve (cranial nerve XI) traced from its cranial and spinal roots into a unified trunk that descends deep to the sternocleidomastoid, then crosses the posterior triangle on its way to the trapezius. The sternocleidomastoid sits anterolaterally, while the trapezius forms the broad superficial muscle of the posterior cervical region and upper back, with the nerve coursing obliquely from superior to inferior and from medial to lateral toward its trapezial entry points. Surrounding shoulder musculature, including deltoid and a portion of latissimus dorsi, frames the distal field, and superficial venous channels are shown in blue as they traverse the lateral neck and shoulder region. Fiber direction is explicit. Good for teaching surface-to-deep relationships. This posterior oblique perspective matters because CN XI is one of the few cranial nerves routinely encountered in lateral neck surgery, where it is susceptible to iatrogenic injury during lymph node biopsy or neck dissection in the posterior cervical triangle. Denervation produces the classic pattern of ipsilateral shoulder droop, impaired scapular upward rotation, and weakness elevating the arm above horizontal, while sparing of the sternocleidomastoid can be variable depending on the level of injury and contribution from C2 to C4. The route across the posterior triangle is the danger zone. Use this illustration for gross anatomy and head and neck modules, operative anatomy teaching for otolaryngology and endocrine surgery, and clinical handouts explaining accessory nerve palsy after cervical node procedures or trauma. It also suits atlas plates and review articles discussing trapezius reinnervation, nerve grafting, or landmarks for nerve monitoring. Anatomical accuracy verified by SciePro's Medical Advisory Board.