Sternocleidomastoid
Musculus sternocleidomastoideus
The most prominent and palpable neck muscle, the sternocleidomastoid flexes the neck bilaterally and rotates the head to the opposite side when working alone. In strength training it is targeted directly with neck-flexion work (e.g. weighted neck harness flexion, head-strap flexion) and is critical for combat-sport athletes, where a strong, resilient SCM helps brace the neck and reduce concussion/whiplash risk.
- Actions
- Cervical flexion (bilateral), Contralateral cervical rotation (unilateral), Ipsilateral cervical lateral flexion (unilateral), Accessory respiration (rib elevation)
- Origin
- Sternal head: anterior surface of the manubrium of the sternum. Clavicular head: medial one-third of the clavicle.
- Insertion
- Mastoid process of the temporal bone and the lateral half of the superior nuchal line of the occipital bone.
- Innervation
- Motor: accessory nerve (CN XI); sensory/proprioception: ventral rami of cervical plexus (C2-C3).
- Blood supply
- Occipital and superior thyroid arteries (with branches of the suprascapular and posterior auricular arteries).
- Heads
- Sternal head, Clavicular head
Tendons Sternocleidomastoid Tendon