ArticlesAnatomyHead and neckNeckSternocleidomastoid muscle

ArticlesAnatomyHead and neckNeckSternocleidomastoid muscle

Sternocleidomastoid muscle

Author: Achudhan Karunaharamoorthy, MD • Reviewer: Dimitrios Mytilinaios, MD, PhD
Last reviewed: October 30, 2023
Reading time: 5 minutes

The sternocleidomastoid muscle is a two-headed neck muscle, which true to its name bears attachments to the manubrium of sternum (sterno-), the clavicle (-cleido-), and the mastoid process of the temporal bone (-mastoid).

It is a long, bilateral muscle of the neck, which functions to flex the neck both laterally and anteriorly, as well as rotate the head contralaterally to the side of contraction.

The muscle is closely related to certain neurovascular structures that pass through the neck on their way either to the head or to the periphery of the body.

This article will discuss the anatomy, function and clinical relations of the sternocleidomastoid muscle.

Key facts
Origins	Sternal head: superior part of anterior surface of manubrium sterni Clavicular head: superior surface of medial third of the clavicle
Insertions	Lateral surface of mastoid process of the temporal bone, Lateral half of superior nuchal line of the occipital bone
Innervation	Accessory nerve (CN XI), branches of cervical plexus (C2-C3)
Blood supply	Superior thyroid artery
Functions	Unilateral contraction: cervical spine: neck ipsilateral flexion, neck contralateral rotation Bilateral contraction: atlantooccipital joint/ superior cervical spine: head/neck extension; Inferior cervical vertebrae: neck flexion; sternoclavicular joint: elevation of clavicle and manubrium of sternum
Clinical relations	Wryneck, torticollis

Contents

Origin and insertion
Relations
Innervation
Blood supply
Function
Clinical relations
Sources

+ Show all

Origin and insertion

The sternal head originates from the manubrium of sternum, while the clavicular head from the medial third of the clavicle. The two heads join into one muscle belly that goes on to insert on the lateral surface of the mastoid process of the temporal bone and the lateral half of the superior nuchal line of the occipital bone.

Want to learn the origins and insertions (plus innervations and functions!) of the sternocleidomastoid muscle 10x faster and easier? You need our head and neck muscle anatomy chart!

Sternocleidomastoid muscle in the neck of the cadaver. Notice its attachments for which it got its name; sterno- (sternum), cleido- (clavicle) and -mastoid (mastoid process).

Relations

The muscle lies very superficially so that it is both easily visible and palpable. The carotid pulse may be felt in the middle third of the front edge. Under the sternocleidomastoid region runs a neurovascular bundle containing:

the common carotid artery (medial)
the internal jugular vein (lateral)
the vagus nerve (dorsal)
the cervical ansa

When putting a central venous catheter (CVC), the medial edge of the sternocleidomastoid muscle serves as a lead structure. Sensory branches of the cervical plexus merge dorsally to the muscle at the Erb’s point (punctum nervosum) which can be used as a place of puncture for local anesthesia.

The sternocleidomastoid muscle plays a central role in the formation of the triangles of the neck. Learn everything about those triangles with the following study unit.

Innervation

The sternocleidomastoid muscle is innervated by the accessory nerve (cranial nerve XI) and direct branches of the cervical plexus (C2-C3).

Blood supply

Blood supply to the sternocleidomastoid muscle is through the superior thyroid artery, which is a branch of the external carotid artery.

Function

A unilateral contraction of the sternocleidomastoid muscle flexes the cervical vertebral column to the same side (lateral flexion) and rotates the head to the opposite side.

A bilateral contraction elevates the head by dorsally extending the upper cervical joints. At the same time, it flexes the lower cervical column causing an overall bending of the neck towards the chest.

If the head is fixed, it elevates the sternum and clavicle and, thus, expands the thoracic cavity (inspiratory breathing muscle).

Test your knowledge about the sternocleidomastoid and other anterior muscles of the neck with the following quiz:

Clinical relations

During pathological changes of the sternocleidomastoid the clinical picture of the wryneck occurs (bending of the head to the affected muscle and rotation to the healthy side). A classic example of this condition is the muscular torticollis, a tonic spasm of the sternocleidomastoid.

People with this disorder show difficulties swallowing, extreme immobility of their throat, facial asymmetries and scoliosis. Approximately 0.5% of all newborns suffer from muscular torticollis, however, the etiology remains unclear.

Sources

All content published on Kenhub is reviewed by medical and anatomy experts. The information we provide is grounded on academic literature and peer-reviewed research. Kenhub does not provide medical advice. You can learn more about our content creation and review standards by reading our content quality guidelines.

References:

D. Drenckhahn, J. Waschke: Taschenbuch Anatomie, Urban & Fischer Verlag/Elsevier (2008), S. 189
M. Schünke/E. Schulte/U. Schumacher: Prometheus – LernAtlas der Anatomie – Allgemeine Anatomie und Bewegungssystem, 2. Auflage, Thieme Verlag (2007), S. 292-293
W. Graumann, D. Sasse: CompactLehrbuch der gesamten Anatomie - Bd.2 - Bewegungsapparat, Schattauer Verlag (2003) S. 462-463
F. Hefti: Kinderorthopädie in der Praxis, 2. Auflage, Springer Verlag (2006), S. 117-120
E. Kennedy, M. Albert, H. Nicholson: The fascicular anatomy and peak force capabilities of the sternocleidomastoid muscle. Surgical and Radiologic Anatomy (2016), Springer-Verlag France, p. 1-17. DOI 10.1007/s00276-016-1768-9

Illustrators:

Neck muscles, nerves and vessels (cadaveric dissection) - Prof. Carlos Suárez-Quian

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