The suprahyoid muscles are a group of four paired muscles located in the anterior region of the neck, situated superiorly to the hyoid bone. This muscle group forms the muscular floor of the mouth, connecting the hyoid bone to structures higher in the head. They are involved in movements necessary for speaking and consuming food. These muscles play a significant role in airway management and are often a focus in surgical procedures involving the floor of the mouth.
Anatomical Placement Relative to the Hyoid Bone
The suprahyoid muscles are positioned within the anterior neck triangle, spanning the space between the base of the mandible and the hyoid bone. The hyoid bone is unique because it does not articulate directly with any other bone; instead, it is suspended and stabilized by a complex network of muscles, including the suprahyoid group. The suprahyoid muscles are arranged in three planes: the geniohyoid is the deepest, the mylohyoid is in the middle, and the digastric and stylohyoid muscles form the superficial layer. They connect the hyoid bone to the skull base and the mandible. This group contrasts functionally with the infrahyoid muscles, which are located inferior to the hyoid bone and primarily function to depress it.
Individual Muscles of the Suprahyoid Group
The suprahyoid group consists of four distinct muscles: the digastric, stylohyoid, mylohyoid, and geniohyoid muscles, each existing as a pair. The digastric muscle is notable for having two muscular sections, or bellies, connected by an intermediate tendon. The posterior belly originates from the mastoid process of the temporal bone, while the anterior belly arises from the digastric fossa on the inner surface of the mandible. This intermediate tendon is held to the hyoid bone by a fibrous sling. The stylohyoid is a long, slender muscle that runs nearly parallel to the posterior belly of the digastric muscle, originating from the styloid process of the temporal bone and inserting onto the lateral aspect of the hyoid bone.
The mylohyoid is a broad, flat, triangular-shaped muscle that forms a muscular diaphragm, creating the structural floor of the mouth. It originates from the mylohyoid line on the inner surface of the mandible and inserts onto a midline fibrous raphe and the body of the hyoid bone. The geniohyoid muscle is a short, narrow muscle located deep to the mylohyoid, positioned close to the midline. It originates from the inferior mental spine of the mandible, also known as the genial tubercle, and attaches to the upper border of the hyoid bone.
Collective Roles in Deglutition and Phonation
The unified action of the suprahyoid muscle group is essential for swallowing (deglutition) and speech (phonation). Their primary combined function is the superior and anterior movement of the hyoid bone and the larynx, which is required for the first stage of swallowing. By elevating the hyoid and larynx, the suprahyoid muscles ensure the airway is closed off by inducing epiglottic deflection, protecting against aspiration. This movement also facilitates the opening of the upper esophageal sphincter, allowing the food bolus to pass into the esophagus.
When the infrahyoid muscles stabilize the hyoid bone, the suprahyoids reverse their action and contribute to depressing the mandible, assisting in the wide opening of the mouth for chewing and yawning. The precise control over the hyoid bone and the floor of the mouth is also integral to speech. The mylohyoid muscle elevates the floor of the mouth and the tongue for articulation. The geniohyoid moves the hyoid bone anteriorly, and the stylohyoid muscle elevates and retracts the hyoid.
Innervation and Associated Clinical Conditions
The suprahyoid muscles have a complex and varied nerve supply, reflecting their diverse embryonic origins. The anterior belly of the digastric muscle and the mylohyoid muscle are innervated by the mylohyoid nerve, a branch of the mandibular division of the trigeminal nerve (Cranial Nerve V). In contrast, the posterior belly of the digastric and the stylohyoid muscle receive their nerve supply from the facial nerve (Cranial Nerve VII). The geniohyoid muscle is innervated by the first cervical spinal nerve (C1) fibers, which travel briefly with the hypoglossal nerve (Cranial Nerve XII).
Damage to these nerves or the muscles themselves can lead to clinical issues. Dysfunction in the suprahyoid group is a common contributor to dysphagia (difficulty or discomfort in swallowing) or problems with speech articulation. Impairment of these muscles or their neurological control can compromise the elevation of the hyoid and larynx, preventing necessary airway protection during swallowing. Dysfunction can also contribute to conditions like obstructive sleep apnea, as the muscles play a role in maintaining airway patency. Understanding this heterogeneous innervation is essential for diagnosing and treating related disorders.