[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Spine](https://durgical.com/en/anatomy/region/spine/) › Sternocleidomastoid [Muscular system](https://durgical.com/en/anatomy/system/muscular-system/) · [Spine](https://durgical.com/en/anatomy/region/spine/) # Sternocleidomastoid The sternocleidomastoid is the large strap muscle on each side of the neck, from the breastbone and collarbone to behind the ear; it turns the head. Official name: Sternocleidomastoid muscle [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=spine&select=sternocleidomastoid&side=r) Opens in the Durgical app, no sign-up needed. ## What it is The large strap muscle on each side of the neck, from the breastbone and collarbone to behind the ear. ## What it does Turns the head to the opposite side and tilts it to the same side; both together bend the neck forward. In an ACDF the incision follows its front edge. ## Key points - Divides each side of the neck into the anterior triangle in front and the posterior triangle behind (with [trapezius](https://durgical.com/en/anatomy/trapezius-muscle/) and the [clavicle](https://durgical.com/en/anatomy/clavicle/)) - The cutaneous nerves of the cervical plexus (lesser occipital, great auricular, transverse cervical, supraclavicular) wind round the middle of its posterior border, the nerve point of the neck - The spinal accessory nerve runs through or deep to its upper part and leaves its posterior border a little above the nerve point to cross the posterior triangle ## Key facts **Origin** Sternal head: anterior [manubrium](https://durgical.com/en/anatomy/manubrium-of-sternum/); clavicular head: medial third of clavicle **Insertion** Mastoid process and lateral half of the superior nuchal line **Action** Unilateral: tilts head to same side, turns face to opposite side; bilateral: flexes neck; accessory inspiration **Nerve** Spinal accessory nerve (CN XI); proprioception C2–C3 **Blood supply** Occipital and superior thyroid arteries (sternocleidomastoid branches) ## Relations **Superficial** [Platysma](https://durgical.com/en/anatomy/platysma/), the [external jugular vein](https://durgical.com/en/anatomy/external-jugular-vein/) crossing it obliquely, and the great auricular and transverse cervical nerves **Deep** [Carotid sheath](https://durgical.com/en/anatomy/carotid-sheath/) (common and internal [carotid arteries](https://durgical.com/en/anatomy/common-carotid-artery/), [internal jugular vein](https://durgical.com/en/anatomy/internal-jugular-vein/), [vagus nerve](https://durgical.com/en/anatomy/vagus-nerve/)), the cervical plexus, the [scalenes](https://durgical.com/en/anatomy/scalenus-anterior-muscle/) and, above, [splenius](https://durgical.com/en/anatomy/splenius-capitis-muscle/) capitis **In front** Anterior triangle of the neck, with its submandibular, submental, carotid and muscular triangles **Behind** Posterior triangle: the spinal [accessory nerve](https://durgical.com/en/anatomy/accessory-nerve/) crossing it, the [brachial plexus trunks](https://durgical.com/en/anatomy/brachial-plexus-trunks/) low down and the inferior belly of [omohyoid](https://durgical.com/en/anatomy/omohyoid-muscle/) **Below** The small hollow between its sternal and clavicular heads lies over the internal jugular vein; this is the lesser supraclavicular fossa (Sédillot triangle), the landmark for the central approach to the internal jugular vein ## How to find it Turning the head to the opposite side against resistance makes the muscle stand out from behind the ear to the sternoclavicular joint; the two heads and the small hollow between them are seen just above the clavicle. ## Examination - Head turn against resistance tests the accessory nerve: weakness turning the face away from a side points to the nerve on that side - Weakness of both sternocleidomastoid and trapezius points to a CN XI lesion high up (skull base, [jugular foramen](https://durgical.com/en/anatomy/jugular-foramen/)); trapezius alone points to the posterior triangle ## On imaging Ultrasound is the first test in an infant with torticollis: the muscle is thickened, sometimes with a focal mass inside it (fibromatosis colli) and normal tissue around it, which usually avoids a biopsy. On neck CT or MRI it is the landmark between the anterior and posterior triangles; the carotid sheath and the level II–IV lymph nodes lie deep to it. ## Clinical notes - Congenital muscular torticollis: a fibrotic, shortened muscle, sometimes with a lump in infancy, tilts the head to the same side and turns the chin to the opposite side - Its anterior border guides incisions for anterior cervical [spine](https://durgical.com/en/anatomy/region/spine/) surgery, carotid endarterectomy and neck dissection - The hollow between its two heads is a landmark for internal jugular vein catheterisation - Often involved in cervical dystonia (spasmodic torticollis), where it is a common target for botulinum toxin injections ## Anatomical variants - Rarely absent; its origins vary, especially the width of the clavicular head ## Development It and trapezius come from a single muscle mass at the back of the developing head, just behind the last pharyngeal arch. The accessory nerve grows into this mass early and is carried down as it spreads toward the shoulder girdle, so both muscles share CN XI; whether the mass is pharyngeal-arch or somite mesoderm is still debated. ## Related conditions - [Whiplash (cervical sprain)](https://durgical.com/en/conditions/whiplash/) - [Torticollis](https://durgical.com/en/conditions/torticollis/) - [Myotonic dystrophy (types 1 and 2)](https://durgical.com/en/conditions/myotonic-dystrophy/) - [Dystonia (generalised and focal)](https://durgical.com/en/conditions/dystonia/) - [Thyroglossal duct cyst and branchial cleft cyst](https://durgical.com/en/conditions/thyroglossal-duct-cyst-and-branchial-cleft-cyst/) ## Test yourself Think of the answer, then tap the question to see it. ## What nerve supplies the sternocleidomastoid? The spinal accessory nerve (CN XI); C2–C3 carry proprioception. ## What does the sternocleidomastoid do when it contracts on one side? It tilts the head to the same side and turns the face to the opposite side; together both flex the neck. ## What is the nerve point of the neck on the sternocleidomastoid? The middle of its posterior border, where the cutaneous cervical plexus nerves wind round. ## What does weakness of both sternocleidomastoid and trapezius suggest? A high CN XI lesion (skull base, jugular foramen); trapezius alone points to the posterior triangle. ## What is congenital muscular torticollis of the sternocleidomastoid? A fibrotic, shortened muscle that tilts the head to the same side and turns the chin to the opposite side. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/anatomy/sternocleidomastoid-muscle/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** musculus sternocleidomastoideus TA2 2156 **Official Spanish (DeCS)** Músculo esternocleidomastoideo DeCS D009334 **English (TA2)** Sternocleidomastoid muscle **Also called** sternomastoid muscle ## Related - [Carotid arteries](https://durgical.com/en/anatomy/common-carotid-artery/) - [Platysma](https://durgical.com/en/anatomy/platysma/) - [Base of the skull](https://durgical.com/en/anatomy/occipital-bone/) Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=9525&filter=ths_termall&q=M%C3%BAsculos%20del%20Cuello); [Anatomy, Head and Neck: Sternocleidomastoid Muscle](https://www.ncbi.nlm.nih.gov/books/NBK532881/); Anatomy of the Human Body (20th ed.): Development of the Muscles (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain; Anatomía humana (4.ª ed.), tomo 1, cap. 19: Músculos del cuello. ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/sternocleidomastoid-muscle/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/sternocleidomastoid-muscle/