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sternocleidomastoid muscle
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Illustration of the human neck showing labeled muscles, arteries, veins, and bones, including the sternocleidomastoid, digastric, mylohyoid, trapezius, carotid artery, jugular vein, clavicle, and thyroid cartilage. An anatomical illustration of the human upper limb and chest from the front, showing labeled muscles such as the deltoid, pectoralis major, biceps, triceps, and serratus anterior, along with the cephalic vein and thoracoacromial artery. An anatomical illustration of the human head and neck in profile, showing the muscles of facial expression with detailed labels identifying each muscle, including those around the eyes, mouth, forehead, and jaw. Illustration of the human back showing labeled muscles including trapezius, deltoid, latissimus dorsi, erector spinae, rhomboids, and gluteus maximus, with detailed anatomical structure.
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sternocleidomastoid muscle

anatomy
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Illustration of the human neck showing labeled muscles, arteries, veins, and bones, including the sternocleidomastoid, digastric, mylohyoid, trapezius, carotid artery, jugular vein, clavicle, and thyroid cartilage.
muscles of the neck; human muscle system Muscles of the neck.

The sternocleidomastoid muscle, also known as the sternomastoid muscle, is a prominent muscle on each side of the neck. It originates from the sternum and clavicle and inserts into the mastoid process and occipital bone.12

This muscle plays a crucial role in head and neck movement. It is primarily responsible for rotating the neck to the opposite side and bending the neck to the same side. When both sternocleidomastoid muscles contract together, they flex the neck, helping to bring the chin towards the chest, and also assist in forced inhalation by raising the sternum. The accessory nerve (CN XI) innervates the sternocleidomastoid muscle, controlling its actions.34

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4 Britannica Sources
  1. sternocleidomastoid
  2. human muscle system - The neck
  3. sternomastoid
  4. human nervous system - Accessory nerve (CN XI or 11)

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