Head and neck muscles (chewing, facial, and throat muscles)

Sternocleidomastoid

Musculus sternocleidomastoideus

Origin

Manubrium of the sternum (sternal head) and the medial third of the clavicle (clavicular head)

Insertion

Mastoid process and the lateral part of the superior nuchal line of the occipital bone

Function

Unilateral contraction: lateral flexion of the head to the same side with rotation to the opposite side; bilateral contraction: flexion of the neck and extension of the head at the upper cervical joints, and an accessory muscle of respiration

Innervation

Accessory nerve (CN XI) motor, with proprioceptive contribution from the cervical plexus (C2–C3)

Movement & chain

Works together with the contralateral scalenes and the deep neck flexors during head rotation and flexion; active as an accessory respiratory muscle during exertion or dyspnea.

Palpation

Clearly visible and palpable from the mastoid to the sternoclavicular joint when the head is rotated and flexed against resistance.

Clinical

Congenital shortening (muscular torticollis) causes a characteristic tilted head posture in infants; myofascial trigger points here can trigger headache and dizziness.

Segmental innervation

Motor via the accessory nerve (XI); sensory/proprioceptive innervation via C2–C3.

In clinical practice

An important landmark during physical examination of the neck (e.g. assessing jugular venous pressure) and for cannulating the internal jugular vein.

Region in the model

Head and neck muscles (chewing, facial, and throat muscles)