The Infrahyoid Muscles PDF

THE INFRAHYOID MUSCLES • The infrahyoid muscles are a group of four muscles that are located inferiorly to the hyoid bone in the neck. • They can be divided into 2 groups. • Superficial plane – omohyoid and sternohyoid muscles. • Deep plane – sternothyroid and thyrohyoid muscles. • The arterial su...

THE INFRAHYOID MUSCLES • The infrahyoid muscles are a group of four muscles that are located inferiorly to the hyoid bone in the neck. • They can be divided into 2 groups. • Superficial plane – omohyoid and sternohyoid muscles. • Deep plane – sternothyroid and thyrohyoid muscles. • The arterial supply to the infrahyoid muscles is via the superior and inferior thyroid arteries, with venous drainage via the corresponding veins. Omohyoid • The omohyoid is comprised of two muscle bellies, which are connected by a muscular tendon. Attachments: • The inferior belly of the omohyoid arises from the scapula. • It runs superomedially underneath the sternocleidomastoid muscle. Omohyoid • It is attached to the superior belly by an intermediate tendon, which is anchored to the clavicle by the deep cervical fascia. • From here, the superior belly ascends to attach to the hyoid bone. Omohyoid Actions: • Depresses the hyoid bone. Innervation: • Anterior rami of C1-C3, carried by a branch of the ansa cervicalis. Sternohyoid • The sternohyoid muscle is located within the superficial plane. Attachments: • Originates from the sternum and sternoclavicular joint. • It ascends to insert onto the hyoid bone. Actions: • Depresses the hyoid bone. Innervation: • Anterior rami of C1-C3, carried by a branch of the ansa cervicalis. Sternothyroid • The sternothyroid muscle is wider and deeper than the sternohyoid. • It is located within the deep plane. Attachments: • Arises from the manubrium of the sternum, and attaches to the thyroid cartilage. Actions: • Depresses the thyroid cartilage. Innervation: • Anterior rami of C1-C3, carried by a branch of the ansa cervicalis. Thyrohyoid • The thyrohyoid is a short band of muscle, thought to be a continuation of the sternothyroid muscle. Attachments: • Arises from the thyroid cartilage of the larynx, and ascends to attach to the hyoid bone. Actions: • Depresses the hyoid. If the hyoid bone is fixed, it can elevate the larynx. Innervation: • Anterior ramus of C1, carried within the hypoglossal nerve.