Sternocleidomastoid - Podcast Version 0:00 / 0:00 1x 0.25x 0.5x 0.75x 1x 1.25x 1.5x 1.75x 2x The sternocleidomastoid is a muscle of the anterolateral aspect of the neck. Attachments: Sternal head originates from the manubrium of the sternum Clavicular head originates from the medial third of the clavicle Both heads attach to the mastoid process of the temporal bone and the superior nuchal line of the occipital bone. Actions: Lateral flexion and rotation of the neck when acting unilaterally, and extension of the neck at the atlanto-occipital joints when acting bilaterally. Innervation: Accessory nerve Blood supply: Upper third – Occipital artery Middle third – Superior thyroid artery and external carotid artery Lower third – Suprascapular artery By TeachMeSeries Ltd (2026) Fig 1- Lateral view of the neck. Note the two heads of the sternocleidomastoid Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Pro Feature - Dissection Atlas Superficial dissection of the neck, demonstrating the platysma and underlying structures. Superficial dissection of the neck, demonstrating the platysma and underlying structures. You've Discovered a Pro Feature Access our Dissection Image Library Enhance your understanding with high-resolution dissection images showcasing real-life anatomy. Learn More Frequent questions What is the sternocleidomastoid muscle? The sternocleidomastoid is a prominent muscle located on the anterolateral side of the neck. It plays a key role in neck movement and is essential for various head positions. What are the attachments of the sternocleidomastoid muscle? The sternocleidomastoid has two heads: the sternal head originates from the manubrium of the sternum, while the clavicular head arises from the medial third of the clavicle. Both heads insert at the mastoid process of the temporal bone and the superior nuchal line of the occipital bone. What actions does the sternocleidomastoid facilitate? When acting unilaterally, the sternocleidomastoid allows for lateral flexion and rotation of the neck. Bilaterally, it aids in the extension of the neck at the atlanto-occipital joints. Which nerve innervates the sternocleidomastoid muscle? The sternocleidomastoid is innervated by the accessory nerve. This nerve is crucial for the muscle's function in head and neck movements. What is the blood supply to the sternocleidomastoid muscle? The blood supply to the sternocleidomastoid muscle varies along its length: the upper third is supplied by the occipital artery, the middle third by the superior thyroid artery and external carotid artery, and the lower third by the suprascapular artery. This vascularisation supports its function and health. Rate This Article