Origin Medial third of superior nuchal line; external occipital protruberance, nuchal ligament, and spinous processes of C7 - T12 vertebrae Insertion Lateral third of clavicle, acromion, and spine of scapula Action Elevates, retracts and rotates scapula; superior fibers elevate, middle fibers retract, and inferior fibers depress scapula; superior and inferior fibers act together in superior rotation of scapula Innervation Spinal root of accessory nerve (CN XI) (motor) and cervical nerves (C3 and C4) (pain and proprioception) (XI, C3, C4) Arterial Supply Transverse cervical artery