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Origins, insertions, innervations and functions of the sternocleidomastoid muscle.
Hello again, everyone. It’s Matt from Kenhub! And in this tutorial, we will discuss the function and anatomy of the sternocleidomastoid muscle.
The sternocleidomastoid muscle is a two-headed muscle of the neck. The two heads are called the sternal head and the clavicular head.
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.
The sternocleidomastoid is innervated by the accessory nerve and by direct branches of the cervical plexus.
The sternal head originates from the sternal manubrium and the clavicular head from the middle part of the clavicle.
The insertion is the mastoid process of the temporal bone and the superior nuchal line of the occipital bone.
Under the sternocleidomastoid region runs a neurovascular bundle containing the common carotid artery, the internal jugular vein, the vagus nerve, highlighted here in green, and the cervical ansa.
A unilateral contraction of the sternocleidomastoid muscle flexes the cervical vertebral column to the same side called lateral flexion and rotates the head to the opposite side.
A bilateral contraction leads to an elevation of the head, otherwise called dorsal extension.
In addition, it supports inspiration, providing that the head is holding still.