Sternocleidomastoid muscle
Citation, DOI, disclosures and article data
Citation:
V, Deng F, A A, et al. Sternocleidomastoid muscle. Reference article, Radiopaedia.org (Accessed on 23 Mar 2025) https://radiopaedia.org/articles/13075
DOI:
-
rID:
13075
Article created:
26 Feb 2011,
Vijay
Disclosures:
At the time the article was created Vijay had no recorded disclosures.
View Vijay's current disclosures
Last revised:
Disclosures:
At the time the article was last revised Francis Deng had no recorded disclosures.
View Francis Deng's current disclosures
Revisions:
18 times, by
14 contributors -
see full revision history and disclosures
Systems:
Sections:
Synonyms:
- Sternocleidomastoid (SCM)
- Sternomastoid muscle
- Sternomastoid
- Sternomastoid muscles
- Sternocleidomastoid muscles
The sternocleidomastoid muscle (also known as sternomastoid) is found in the neck. It has two heads that meld to form one insertion. Sternocleidomastoid muscle, along with the trapezius muscle, is invested by the superficial layer of the deep cervical fascia, which splits around it. Sternocleidomastoid muscle divides the neck into anatomical anterior and posterior triangles.
On this page:
Summary
- origin: manubrium, medial clavicle
- insertion: mastoid process, superior nuchal line
- innervation: accessory nerve (CN XI)
- action: lateral flexion, flexion and rotation of the head on the neck
Gross anatomy
Origin
- sternal head (round and tendinous): upper part of anterior surface of manubrium of sternum
- clavicular head (thin and broader fleshy): upper surface of medial third of clavicle
Course
- sternal head passes over the sternoclavicular joint and joins the clavicular head halfway up the neck
- common muscle belly then courses posterolaterally to its insertion
Insertion
- mastoid process of temporal bone
- lateral half of the superior nuchal line of the occipital bone
Relations
-
upper half
- posteriorly: cervical plexus, which emerges from behind the lateral border of sternocleidomastoid muscle with some branches (lesser occipital, greater auricular and transverse cervical nerves) coursing anteriorly
- anteriorly: platysma muscle, external jugular vein
-
lower half
- posteriorly: anterior scalene muscle, common carotid artery, internal jugular vein, carotid sheath
- anteriorly: platysma
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Arterial supply
- superior thyroid and occipital arteries (both branches of the external carotid artery)
Innervation
- spinal part (C2, C3) of the accessory nerve (cranial nerve XI)
- the nerve descends and enters the muscle from its deep surface
Action
- when acting unilaterally: lateral flexion of neck to same side, rotates head to opposite side
- when acting bilaterally: flexes neck, draws head ventrally and elevates chin, draws sternum superiorly in deep inspiration
Variant anatomy
- absent mastoid insertion (occipital insertion only)
- absent clavicular or sternal head
- fusion with trapezius muscle
- additional clavicular head
- separate muscle bellies for sternomastoid and cleidomastoid
- separate muscle bellies for cleido-occipital and sternocleidomastoid
- doubles or quadrupled unilaterally or bilaterally
- absent unilaterally or bilaterally
Related pathology
Quiz questions
References
- 1. Stone RJ, Stone JA. Atlas of skeletal muscles. McGraw-Hill Companies. (2003) ISBN:0071199012. Read it at Google Books - Find it at Amazon
- 2. McMINN. Lasts Anatomy Regional and Applied. CHURCHILL LIVINGSTONE. (2003) ISBN:B0084AQDG8. Read it at Google Books - Find it at Amazon
- 3. Moore KL, Agur AMR, Dalley AF. Clinically oriented anatomy. LWW. ISBN:1451119453. Read it at Google Books - Find it at Amazon
- 4. Hasan T. Variations of the sternocleidomastoid muscle: a literature review. The Internet Journal of Human Anatomy. 2011;1 (1).
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- Occipital bone
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- Subperiosteal abscess of the mastoid
- Carotid body tumor
- Internal jugular vein
Cases:
- Papillary thyroid carcinoma
- Second branchial cleft cyst
- Cystic lymphangioma of the neck
- Fourth branchial cleft cyst and fistula
- Posterior sternoclavicular joint dislocation - ultrasound
- Fibromatosis colli
- Fibromatosis colli
- Second branchial cleft cyst
- Sternocleidomastoid muscle abscess
- Intramuscular lipoma of the sternocleidomastoid muscle
- Second branchial cleft cyst
- Fibromatosis colli
- Second branchial cleft cyst
- Infected second branchial cleft cyst
- Haemangioma - intramuscular
- Cystic hygroma
- Second branchial cleft cyst
- Fibromatosis colli
- Parotid abscess
- Septic pulmonary emboli and chest wall abscess
Multiple choice questions:
Related articles: Anatomy: Head and neck
- skeleton of the head and neck
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cranial vault
- scalp (mnemonic)
- fontanelle
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sutures
- calvarial
- facial
- frontozygomatic suture
- frontomaxillary suture
- frontolacrimal suture
- frontonasal suture
- temporozygomatic suture
- zygomaticomaxillary suture
- parietotemporal suture (parietomastoid suture)
- occipitotemporal suture (occipitomastoid suture)
- sphenofrontal suture
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- spheno-occipital suture (not a true suture)
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- temporal bone
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facial bones
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facial muscles
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orbicularis oris muscle
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- incisivus labii inferioris muscle
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orbicularis oris muscle
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- muscles of the middle ear
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suboccipital muscles
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- deep cervical fascia
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deep spaces of the neck
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- buccal space
- carotid space
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- deep cervical fascia
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arterial supply
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common carotid artery
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common carotid artery
- venous drainage
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arterial supply
- innervation of the head and neck
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cranial nerves
- olfactory nerve (CN I)
- optic nerve (CN II)
- oculomotor nerve (CN III)
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-
trigeminal nerve (CN V) (mnemonic)
- trigeminal ganglion
- ophthalmic division
- maxillary division
- mandibular division
- abducens nerve (CN VI)
- facial nerve (CN VII)
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vestibulocochlear nerve (CN VIII)
- vestibular ganglion (Scarpa's ganglion)
- glossopharyngeal nerve (CN IX)
- vagus nerve (CN X)
- (spinal) accessory nerve (CN XI)
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cervical plexus
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ansa cervicalis
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- contribution to the accessory nerve (CN XI)
- cutaneous branches
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cranial nerves
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