The sternocleidomastoid muscle flexes the neck and helps with movement of the head. Also, the muscle works with the scalene muscles in the neck during forced inspiration while breathing (inhaling), and it raises the sternum, the bone at the front of the rib cage.
The muscle originates at the central portion of the collarbone. It inserts into the temporal bone's mastoid process near the ear and the base of the skull, and it stretches the entire length of the neck. This muscle helps the neck to turn to the side, flex to the side, and bend forward.
Two nerves serve the sternocleidomastoid muscle. For motor functions (movement), the muscle uses the accessory nerve. The cervical plexus nerve provides for sensory function, which includes proprioception — the sense we have of our body’s position and movement within the space around us. This function applies only to the inner workings of the body. For this muscle, proprioception involves becoming aware of pain and transmitting signals to the brain.
Two arteries serve the sternocleidomastoid. Oxygenated blood arrives at the muscle via the occipital artery in the head and superior thyroid artery in the neck.