Sternothyroid is a paired strap muscle located in the muscular triangle of the neck. It is a part of a group of muscles called the infrahyoid muscles. There are four such muscles that are grouped into superficial and deep layers.
The superficial layer includes sternohyoid and omohyoid, while the deep layer is made up of sternothyroid and thyrohyoid. The infrahyoid muscles are also part of a larger group called the extrinsic laryngeal muscles. These muscles help to stabilize the hyoid bone and are important for speech and swallowing.
This article will discuss the anatomy and neurovascular supply of the sternothyroid muscle.
|Origin||Posterior surface of manubrium of sternum, Costal cartilage of rib 1|
|Insertion||Oblique line of thyroid cartilage|
|Action||Depress the larynx|
|Innervation||Anterior rami of C1-3 (via the ansa cervicalis)|
|Blood supply||Superior thyroid and lingual arteries|
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.
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.
The anterior rami of the first three cervical spinal nerves (C1-3) provide motor innervation to sternothyroid by way of the ansa cervicalis.
Blood is supplied to sternothyroid by the branches of the lingual and superior thyroid arteries.
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.
The sternothyroid muscle may be divided during thyroidectomy (removal of the diseased thyroid gland). This allows the surgeon to gain access to the superior pedicle of the gland. To date, there is no evidence to support any relationship between the division of this muscle and adverse functional outcomes postoperatively.