Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Musculoskeletal System
Muscular System
Neck Muscles

The neck Muscles proper include those located in its anterior and lateral regions, which are divided into superficial and deep muscles.

The Superficial neck muscles include the paired platysma (which originates, develops, and Functions as a Muscle of facial expression), the sternocleidomastoid, suprahyoid, and infrahyoid muscles. The deep muscle group comprises the scalene and prevertebral muscles.

The platysma is a thin, flat muscle situated immediately beneath the Skin. It originates from the superficial pectoral fascia and the subcutaneous tissue below the clavicle, runs upward, and blends with the parotid-masseteric fascia and the Tissues of the angle of the Mouth. When it contracts, the muscle pulls the angle of the mouth downward and draws the skin of the neck forward, protecting superficial Veins from compression.

The sternocleidomastoid muscle originates by two heads from the Sternum and clavicle and inserts into the mastoid process of the Temporal bone. Bilateral contraction of these muscles tilts the HEAD backward. Unilateral contraction flexes the head toward the same side while simultaneously rotating it in the opposite direction.

The suprahyoid group unites the paired digastric, stylohyoid, geniohyoid, and mylohyoid muscles, all of which attach to the Hyoid bone. The digastric muscle has two bellies (anterior and posterior) with an intermediate tendon between them. The anterior belly originates from the digastric fossa of the Mandible, while the posterior belly attaches to the mastoid notch of the temporal bone. The intermediate tendon connecting both bellies is anchored to the hyoid bone by a fibrous loop. This muscle elevates the hyoid bone or, when the hyoid is fixed, depresses the mandible. The stylohyoid muscle originates from the styloid process of the temporal bone. The geniohyoid muscle originates from the mental spine of the mandible. The mylohyoid muscle originates from the inner surface of the mandible. Joining its counterpart from the opposite side, the mylohyoid forms the floor of the Oral Cavity—its Diaphragm—upon which the Tongue rests. All these muscles, by attaching to the hyoid bone, stabilize it; when the hyoid bone is fixed, the geniohyoid and mylohyoid muscles depress the mandible.

The infrahyoid muscles include the sternohyoid, omohyoid, sternothyroid, and thyrohyoid muscles. The sternohyoid muscle originates from the sternum, attaches to the hyoid bone, and pulls it downward. The omohyoid muscle has two bellies (superior and inferior) connected by an intermediate tendon. It originates from the scapula and inserts into the hyoid bone. The sternothyroid muscle originates from the manubrium of the sternum and inserts into the thyroid Cartilage. It depresses the Larynx and hyoid bone. The thyrohyoid muscle extends from the thyroid cartilage to the hyoid bone, elevating the larynx.

All suprahyoid and infrahyoid muscles stabilize the hyoid bone and, consequently, the larynx.

The deep neck muscles include the paired anterior, middle, and posterior scalene muscles, as well as the prevertebral muscles—the longus capitis and longus colli, and the anterior and lateral rectus capitis muscles. The scalene muscles originate from the transverse processes of the cervical vertebrae and insert into the Ribs: the anterior and middle scalene into the first rib, and the posterior into the second. When they contract, the scalene muscles elevate the ribs, participating in the act of inspiration.

The longus capitis and longus colli muscles, along with the rectus capitis anterior, flex the head and the cervical spine forward. The rectus capitis lateralis tilts the head to its own side.