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Spinal Accessory Nerve
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| Spinal Accessory Nerve | |
|---|---|
| Nerve Type | |
| Origin | Arises chiefly from motor neurons in the spinal accessory nucleus (C1–C5/6) with a small cranial root from the medulla that soon joins the vagus. |
| Course | Spinal rootlets ascend through the foramen magnum, unite with the cranial root, exit via the jugular foramen, supply sternocleidomastoid deep to the muscle, then traverse the posterior triangle on levator scapulae to enter the trapezius with C2–C4 proprioceptive twigs. |
| Major Branches | Muscular branches to sternocleidomastoid and trapezius, communicating branches with the C2–C4 cervical plexus, and a small meningeal branch near the jugular foramen. |
| Sensory innervation | No cutaneous field; proprioceptive afferents for sternocleidomastoid and trapezius run via C2–C4 cervical plexus |
| Motor innervation | Sternocleidomastoid and Trapezius |
| Conditions | Accessory nerve palsy causes shoulder droop, impaired abduction above 90°, lateral Scapular Winging, and muscle atrophy, commonly from posterior triangle lymph node biopsy, neck dissections, carotid–jugular procedures, trauma, or iatrogenic stretch/compression. |
