The genioglossus is the largest of the tongue’s extrinsic muscles, forming the majority of its bulk. This fan-shaped muscle is fundamental to tongue movement, enabling actions from simple protrusion to more complex shaping. Its function is integral to several physiological processes that are often taken for granted.
Anatomy and Core Movements
The genioglossus muscle originates from a small tendon on the superior mental spine on the inner surface of the mandible, or jawbone. From this narrow origin, its fibers fan out superiorly and posteriorly. The superior fibers travel up and forward to insert along the tongue’s top surface, blending with its intrinsic muscles, while the inferior fibers pass downward to attach to the hyoid bone in the neck.
This muscular structure facilitates several distinct actions of the tongue. When both sides of the genioglossus contract together, they depress the central part of the tongue and protrude its tip forward. If only one side of the muscle contracts, it results in the tongue deviating to the opposite side. Specific parts of the muscle control different motions; for instance, the anterior fibers pull the tongue forward and down, while posterior fibers help move the tongue’s base forward.
The muscle is histologically diverse, with different fiber types concentrated in specific regions to support its functions. The anterior portion contains a significant number of type II fibers, suited for rapid actions like tongue protrusion. In contrast, the posterior portion has fewer type II fibers but possesses considerable strength.
Role in Maintaining an Open Airway
A primary function of the genioglossus is to maintain an open upper airway. The muscle exhibits constant, low-level electrical activity, known as muscle tone, which holds the tongue in a forward position. This prevents the tongue from falling backward into the pharynx, the part of the throat behind the mouth and nasal cavity. This action is important when an individual is lying on their back, as gravity would otherwise cause the tongue to obstruct airflow.
The relaxation of the genioglossus muscle during sleep is a central factor in Obstructive Sleep Apnea (OSA). In those with OSA, the muscle tone diminishes significantly during sleep compared to individuals without the condition. This loss of tone allows the tongue to collapse backward, leading to a partial or complete blockage of the pharyngeal airway. This obstruction causes an apneic event, where breathing stops temporarily.
These events trigger a brief arousal from sleep to restore muscle tone and reopen the airway, often with a loud snort or gasp. The repetitive cycle of obstruction and arousal fragments sleep and reduces blood oxygen levels, contributing to the health consequences associated with OSA. The posterior portion of the muscle is thought to be particularly responsible for maintaining airway patency.
Involvement in Speech and Swallowing
The genioglossus is deeply involved in the processes of speech and swallowing. For articulation, fine motor control of the muscle is necessary to produce a wide array of sounds. By precisely positioning and shaping the tongue, the genioglossus helps form constrictions against the palate and teeth, which modulates airflow to create distinct phonemes. For example, producing ‘k’ and ‘g’ sounds requires the back of the tongue to make firm contact with the soft palate.
During the oral phase of swallowing, known as deglutition, the genioglossus helps manipulate and position food in the mouth. It creates a groove in the tongue’s surface, channeling the food bolus toward the back of the oral cavity. The muscle then assists in propelling the bolus from the mouth into the pharynx for the next stage of swallowing.
Exercises and Medical Interventions
For individuals with weakness in the genioglossus, often associated with OSA, specific exercises can improve muscle tone and function. Myofunctional therapy consists of a regimen of tongue exercises designed to strengthen the genioglossus and other oral muscles. These exercises might include pressing the tongue tip against the roof of the mouth, extending the tongue out and down, and other movements aimed at increasing muscle endurance.
When conservative approaches like therapy are insufficient, medical interventions may be considered. One such treatment is hypoglossal nerve stimulation. This involves implanting a device that delivers mild electrical stimulation to the hypoglossal nerve, which controls the genioglossus. The stimulation is synchronized with breathing during sleep, causing the muscle to contract and pull the tongue forward, thereby keeping the airway open.
Surgical options also exist for more severe cases. A procedure known as genioglossus advancement involves surgically moving the small section of the mandible where the muscle attaches. Pulling this bone segment forward tightens the genioglossus muscle and permanently moves the tongue base away from the back of the throat, enlarging the airway.