Written by Oliver Jones

Last updated October 4, 2023 • 4 Revisions •

The sternocleidomastoid is a muscle of the anterolateral aspect of the neck.

  • Attachments: 
    • Sternal head originates from the manubrium of the sternum
    • Clavicular head originates from the medial third of the clavicle
    • Both heads attach to the mastoid process of the temporal bone and the superior nuchal line of the occipital bone.
  • Actions: Lateral flexion and rotation of the neck when acting unilaterally, and extension of the neck at the atlanto-occipital joints when acting bilaterally.
  • Innervation: Accessory nerve
  • Blood supply:
    • Upper third – Occipital artery
    • Middle third – Superior thyroid artery and external carotid artery
    • Lower third – Suprascapular artery

Fig 1- Lateral view of the neck. Note the two heads of the sternocleidomastoid

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