Anatomy
Summary
The sternocleidomastoid muscle, or SCM, is a paired muscle located superficially in the neck. It has a dual origin from the sternum and clavicle, coming together to connect with the mastoid process of the temporal bone. The sternocleidomastoid is innervated by the accessory nerve, or cranial nerve XI.
When the left SCM contracts, the head turns towards the right. The action is not due to the nerve crossing the midline, but because the muscle pulls the mastoid process medially, turning the head to the contralateral side. Simultaneous contraction of both sternocleidomastoid muscles causes the neck to flex forward. Lateral neck flexion towards the ipsilateral side is achieved when the SCM on the same side contracts. In addition, the SCM is one of the accessory muscles of inspiration and serves as a landmark for identifying the carotid artery.
Lesson Outline
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FAQs
The sternocleidomastoid is involved in various movements of the head and neck. It facilitates the rotation of the head towards the contralateral side. When both sternocleidomastoid muscles contract together, they flex or bend forward the neck. Finally, the sternocleidomastoid assists in the lateral flexion of the neck to the ipsilateral side.
The sternocleidomastoid muscle is primarily innervated by the accessory nerve, also known as cranial nerve XI.
The sternocleidomastoid is considered one of the accessory muscles of inspiration.
The sternocleidomastoid muscle lies superficial to the carotid artery in the neck. As a result, this anatomical position is protective of the artery and serves as a landmark.
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