C5 Root of the Brachial Plexus

Description

Emerging from the intervertebral foramen of C4 to C5, the C5 ventral ramus is traced as it passes laterally in the posterior triangle of the neck, coursing between the anterior and middle scalene muscles before joining the adjacent C6 root to form the superior trunk of the brachial plexus. Superficial to this neurovascular plane, the sternocleidomastoid occupies an anterolateral position, while the trapezius lies more posteriorly toward the shoulder. Inferiorly, the clavicle and scapula frame the supraclavicular region, with the humeral head positioned lateral and distal at the glenohumeral joint. Small arterial and venous channels run in close proximity to the nerve elements. Tight anatomy. This segment is the setup for both function and failure: C5 fibers contribute prominently to the suprascapular nerve and axillary nerve, so traction injuries that depress the shoulder and laterally flex the neck often present with weakness of shoulder abduction and external rotation (classic upper trunk pattern, as in Erb-Duchenne palsy). For procedural anatomy, the relationship of the C5 root to the scalene interval and nearby vessels matters during interscalene brachial plexus block, where local anesthetic spread can affect adjacent structures and where anatomic variation can change needle-to-nerve geometry. The scalene triangle is a frequent site of neurogenic thoracic outlet symptoms, and clear depiction of the root’s path helps explain why symptoms can be posture-dependent. Ideal for brachial plexus teaching in gross anatomy, regional anesthesia curricula, and surgical atlases covering supraclavicular exposure, scalenectomy, or nerve exploration after traction injury; it also supports patient-facing diagrams for upper plexus neuropathy and rotator cuff related referral patterns. Anatomical accuracy verified by SciePro's Medical Advisory Board.