QS Study

Infrahyoid Muscles and their Nerve Supply

Developmentally, the infrahyoid muscles are the derivatives of the longitudinal muscle sheet that goes vertically from the symphysis menti to pubic symphysis. These muscles are a group of four muscles that are located inferiorly to the hyoid bone in the neck.

(A) Sternohyoid muscle; It is located within the superficial plane. It ascends to insert onto the hyoid bone.

Actions: Depresses the hyoid bone.

(B) Sternothyroid muscle; It is wider and deeper than the sternohyoid. It is located within the deep plane.

Actions: Depresses the thyroid cartilage.

(C) Thyrohyoid muscle; It is a short band of muscle, thought to be a continuation of the sternothyroid muscle.

Actions: Depresses the hyoid. If the hyoid bone is fixed, it can elevate the larynx.

(D) Omohyoid muscle; It is comprised of two muscle bellies, which are connected by a muscular tendon.

Actions: Depresses the hyoid bone.

infrahyoid muscles 1

Fig: Infrahyoid Muscles

Nerve supply of the muscles – The sternohyoid, omohyoid and thyrohyoid are supplied by the ansa cervicalis and its superior root. The thyrohyoid is innervated directly by a branch from the hypoglossal nerve taking fibers of ventral ramus of C1.

  1. Sternohyoid muscle: Ansa cervicalis (C 1, 2, & 3). Anterior rami of C1-C3, carried by a branch of the ansa cervicalis.
  2. Sternothyroid muscle: Ansa cervicalis (C 1, 2, & 3). Anterior rami of C1-C3, carried by a branch of the ansa cervicalis.
  3. Thyrohyoid muscle: C1 through the hypoglossal nerve. Anterior ramus of C1 carried within the hypoglossal nerve.
  4. Omohyoid muscle: Ansa cervicalis. Anterior rami of C1-C3, carried by a branch of the ansa cervicalis.
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