Anterior Neck - LO4
4. What are the actions of the sternocleidomastoid (SCM) muscles? What innervates these muscles?
4. What are the actions of the sternocleidomastoid (SCM) muscles? What innervates these muscles?
Sternocleidomastoid m. basics:
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.
