Sternocleidomastoid origin and insertion

Sternocleidomastoid runs from the manubrium and clavicle to the temporal bone and occipital bone.

What are the origin and insertion of sternocleidomastoid?

Sternocleidomastoid arises from the front of the manubrium (sternal head) and the medial third of the clavicle (clavicular head). It inserts on the mastoid process and the lateral half of the superior nuchal line. Its main action is turning the head to the opposite side. It is supplied by the accessory nerve, cranial nerve XI, with C2 and C3 for sensation. The attachments, actions and nerve follow Gray (1918).

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Every attachment and its bone

Origins 2

Origins of sternocleidomastoid, with the bone each is on
Attachment	Bone
Front of the manubrium, sternal head	Manubrium
Medial third of the clavicle, clavicular head	Clavicle

Insertions 2

Insertions of sternocleidomastoid, with the bone each is on
Attachment	Bone
Mastoid process	Temporal bone
Lateral half of the superior nuchal line	Occipital bone

Actions

The actions of sternocleidomastoid, and which are its main ones
Action	What moves	Main or assisting
Turning the head to the opposite side		Main action
Neck flexion, both muscles together	The chin comes down to the chest	Assists

Each action is stated in the anatomical position: standing, arms by the sides, palms forward.

Innervation

The accessory nerve, cranial nerve XI, with C2 and C3 for sensation.

Sources

Gray (1918), Myology, the lateral cervical muscles

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