Anatomy of the Hyoid Bone and Laryngeal Muscles

Laryngeal Skeleton and Hyoid Bone

The hyoid bone is located in the skeleton of the larynx and is formed by various cartilages.

Key Laryngeal Cartilages

• Hyoid Bone: An irregular bone featuring two processes on each side.
• Thyroid Cartilage: Shaped like an "open book" with a prominent thyroid notch. It features superior and inferior prolongations on its side plates.
• Cricoid Cartilage: An unpaired cartilage that articulates posteriorly with the arytenoid cartilage.
• Epiglottic Cartilage: Shaped like a bicycle saddle.

These structures are reinforced by membranes, tendons, and laryngeal muscles, all covered by the laryngeal mucosa.

Hyoid Muscle Groups

The hyoid muscles are located in the anterior neck and are divided into suprahyoid and infrahyoid groups.

Infrahyoid Muscles

These slender, strap-like muscles are situated below the hyoid bone.

Deep Layer

• Sternothyroid: Originates at the manubrium and 1st costal cartilage; inserts on the lateral lamina of the thyroid cartilage. Innervated by the 2nd branch of the hypoglossal loop.
• Thyrohyoid: Originates on the external surface of the thyroid cartilage; inserts on the outer third of the body and root of the greater horn of the hyoid. Innervated by the 1st branch of the hypoglossal loop.

Superficial Layer

• Sternohyoid: Originates at the posterior sternal handle, clavicle, and 1st costal cartilage; inserts on the hyoid body. Innervated by the 4th to 6th branches of the hypoglossal loop.
• Omohyoid: Originates at the superior edge of the scapula; inserts on the inferior edge of the hyoid. Innervated by the 3rd and 5th branches of the hypoglossal loop.

Ansa Cervicalis and Innervation

Cranial nerve XII (hypoglossal) innervates the tongue and binds with cervical nerve branches (C1, C2, C3) to form the ansa cervicalis, which provides motor innervation to these muscles.

Muscle Actions and Relations

The infrahyoid muscles act indirectly on head and neck flexion. The omohyoid tenses the cervical fascia, favoring venous return, and assists in respiration. These muscles are covered by the sternocleidomastoid, the scalene muscles, and the platysma.

Suprahyoid Muscles

• Geniohyoid: Originates at the genial tubercles of the mandible; inserts on the hyoid body. Innervated by the 1st branch of the hypoglossal loop.

Action: Elevates the hyoid when infrahyoid muscles are relaxed. When acting with masticatory muscles, it assists in head and neck flexion; when masticatory muscles are relaxed, it assists in opening the mouth. It is related to the mylohyoid muscle and the tongue.