Learning objective
By the end of this section, the learner should be able to identify the infrahyoid muscles, describe their attachments, actions, and innervation, and explain their functional role in swallowing and laryngeal movement.
The infrahyoid muscles are a group of four strap-like muscles located inferior to the hyoid bone in the anterior neck. Their primary role is to depress the hyoid bone and larynx, providing a stable base for tongue movements during swallowing and speech.
They are arranged in two anatomical planes:
- Superficial plane
- Omohyoid
- Sternohyoid
- Deep plane
- Sternothyroid
- Thyrohyoid
Blood supply:
- Superior thyroid artery
- Inferior thyroid artery
Venous drainage:
- Corresponding thyroid veins
Omohyoid
The omohyoid is a distinctive muscle with two bellies connected by an intermediate tendon, which helps maintain tension in the cervical fascia.
Attachments
- Superior belly: hyoid bone
- Inferior belly: scapula
- The intermediate tendon is anchored to the clavicle by the deep cervical fascia
Action
- Depresses the hyoid bone
Innervation
Anterior rami of C1–C3 via the ansa cervicalis
Sternohyoid
The sternohyoid is a long, flat muscle located in the superficial plane, medial to the omohyoid.
Attachments
- Origin: sternum and sternoclavicular joint
- Insertion: hyoid bone
Action
- Depresses the hyoid bone
Innervation
- Anterior rami of C1–C3 via the ansa cervicalis
Sternothyroid
The sternothyroid lies deep to the sternohyoid and acts primarily on the larynx rather than the hyoid.
Attachments
- Origin: manubrium of the sternum
- Insertion: thyroid cartilage
Action
- Depresses the thyroid cartilage (larynx)
Innervation
- Anterior rami of C1–C3 via the ansa cervicalis
Thyrohyoid
The thyrohyoid is a short muscle considered a continuation of the sternothyroid.
Attachments
- Origin: thyroid cartilage
- Insertion: hyoid bone
Actions
- Depresses the hyoid bone
- Elevates the larynx when the hyoid is fixed
Innervation
- C1 fibers traveling with the hypoglossal nerve
Key functional summary (exam focus)
- Suprahyoids elevate the hyoid → initiate swallowing
- Infrahyoids depress the hyoid and larynx → allow tongue movement
- Ansa cervicalis (C1–C3) innervates all infrahyoids except thyrohyoid
- Thyrohyoid = C1 via hypoglossal nerve
