Anterior Neck - LO4

Sternocleidomastoid m. and trapezius m. are both efferently (motor) innervated by the accessory n. (CN XI). The accessory n. is strictly efferent; therefore, afferent supply to these muscles comes from ventral primary rami of cervical nerves (C2-C4). Typically, C2-C3 (sometimes C4) afferently serve the SCM, whereas C3-C4 afferently serve the trapezius. It is likely that C2-C4 also carry some motor fibers.