Anatomy

Origin

Sternal head—manubrium of sternum Clavicular head—medial part of clavicle

Insertion

Mastoid process of temporal bone, lateral half of superior nuchal line of occipital bone

Nerve

Spinal part of accessory nerve (C2, C3)

Actions

Unilateral—bends neck laterally, rotates head to opposite side Bilateral—flexes neck, draws head ventrally and elevates chin, draws sternum superiorly in deep inspiration