Sternothyroid muscle

Origin and insertion

Sternothyroid is comparatively wider and shorter when compared to the other infrahyoid muscles. It originates from the posterior edge of the costal cartilage of the first rib as well as the posterior surface of the manubrium of the sternum.

At its origin, the muscle is in contact with the contralateral sternothyroid. However, the vertically oriented fibers diverge as they travel superiorly to insert on the oblique line of the thyroid cartilage. Here, the muscle outlines the upper limit of the thyroid gland. This, together with the sternohyoid muscle, limits the cranial extension of an enlarged thyroid gland.

Get the bigger picture of the infrahyoid muscles and other muscles of the ventral neck by reviewing the study unit below.

Relations

Sternothyroid has numerous important anatomical relationships to neurovascular and glandular structures of the neck. It is crossed anteriorly by the oblique fibers of the sternohyoid and the superior belly of omohyoid. On either side of the neck, the muscle is anterior to the lateral lobe of the thyroid gland.

The muscle lies anterior to the brachiocephalic trunk on the right and the common carotid artery and brachiocephalic vein on the left. It is also anterior to the external laryngeal nerve and the superior thyroid artery. The cervical part of the trachea and the inferior pharyngeal constrictor are crossed by sternothyroid.

Innervation

The anterior rami of the first three cervical spinal nerves (C1-3) provide motor innervation to sternothyroid by way of the ansa cervicalis.

Blood supply

Blood is supplied to sternothyroid by the branches of the lingual and superior thyroid arteries.

Functions

Collectively with the other infrahyoid muscles, sternothyroid pulls the hyoid and larynx downward to their resting positions. This process reopens the laryngeal inlet after swallowing so that respiration can resume. This downward movement is also important when singing low notes.

When acting alone, the sternothyroid muscle pulls the lamina of the thyroid cartilage away from the hyoid bone, thus opening the laryngeal inlet. This is particularly beneficial during forced inspiration so that air enters the lower airway.