Infrahyoid muscles

The infrahyoid muscles are a group of four paired muscles located in the anterior neck, inferior to the hyoid bone. They are commonly referred to as the “strap muscles” due to their flat, ribbon-like appearance. Their primary function is to depress the hyoid bone and larynx during swallowing and speech, and to stabilize the hyoid for tongue movement and suprahyoid muscle function.

Location

These muscles are positioned in the anterior triangle of the neck, deep to the platysma and superficial layer of the deep cervical fascia. They extend between the hyoid bone, sternum, clavicle, and scapula.

List of Infrahyoid Muscles

The infrahyoid muscle group includes:

• Sternohyoid
• Omohyoid (superior and inferior bellies)
• Sternothyroid
• Thyrohyoid

Individual Muscles

Sternohyoid

• Origin: Posterior surface of manubrium of sternum and medial end of clavicle
• Insertion: Body of hyoid bone
• Innervation: Ansa cervicalis (C1–C3)
• Function: Depresses the hyoid bone after it has been elevated

Omohyoid

• Origin: Superior border of scapula near the suprascapular notch
• Insertion: Inferior border of the body of hyoid bone
• Innervation: Ansa cervicalis (C1–C3)
• Function: Depresses and stabilizes the hyoid bone
• Special Feature: Has two bellies (superior and inferior) connected by an intermediate tendon anchored to the clavicle by a fascial sling

Sternothyroid

• Origin: Posterior surface of manubrium of sternum
• Insertion: Oblique line of the thyroid cartilage
• Innervation: Ansa cervicalis (C2–C3)
• Function: Depresses the larynx (thyroid cartilage)

Thyrohyoid

• Origin: Oblique line of the thyroid cartilage
• Insertion: Inferior border of the body and greater horn of the hyoid bone
• Innervation: C1 fibers via the hypoglossal nerve (CN XII)
• Function: Depresses the hyoid bone or elevates the larynx when the hyoid is fixed

Function

The infrahyoid muscles collectively perform the following functions:

• Depression of the hyoid bone after elevation during swallowing
• Stabilization of the hyoid for tongue and suprahyoid muscle activity
• Depression of the larynx (especially sternothyroid and thyrohyoid)

Innervation

• Sternohyoid, Omohyoid, Sternothyroid: Ansa cervicalis (C1–C3)
• Thyrohyoid: C1 via hypoglossal nerve (CN XII)

Blood Supply

• Superior thyroid artery (branch of external carotid artery)
• Inferior thyroid artery (branch of thyrocervical trunk)

Clinical Relevance

• Tracheostomy landmarking: Infrahyoid muscles are encountered and sometimes retracted during surgical airway access.
• Neck dissections: These muscles are important anatomical landmarks during cervical lymph node dissection.
• Hypoglossal nerve injury: May affect thyrohyoid function if C1 fibers are involved.