Tongue Elongation and Protrusion
The intrinsic transverse muscle (transversus linguae) is primarily responsible for tongue elongation, working in concert with the intrinsic vertical muscle to compress and elongate the tongue body, while the genioglossus muscle establishes anterior-posterior positioning during protrusion. 1
Mechanism of Tongue Elongation
The tongue functions as a muscular hydrostat, where elongation occurs through a specific biomechanical process:
The transversus linguae (transverse intrinsic muscle) fibers envelope and compress the longitudinal muscle fascicles, resulting in tongue elongation through a hydrostat mechanism where compression in one dimension causes extension in another. 1
Alternating sheets of transverse and vertical lingual muscles insert into the circumference of the tongue, with transverse muscle fibers completely encircling longitudinal muscle fascicles to produce the compressive force needed for elongation. 1
Division of Labor During Protrusion
The act of tongue protrusion involves coordinated activation of multiple muscle groups with distinct roles:
The genioglossus muscle is more important for establishing anterior-posterior tongue location rather than generating protrusive force, as genioglossus EMG activity changes faithfully with tongue position but remains relatively constant as protrusion force increases. 2
Intrinsic tongue muscles (transverse and vertical) play a greater role in generating actual protrusive force, with significantly higher intrinsic muscle activity observed during impeded protrusion tasks compared to genioglossus activity. 2
Both genioglossus and intrinsic protrusor muscles are simultaneously active during protrusion, but the intrinsic muscles appropriately follow changes in both tongue position and force, while genioglossus primarily tracks position. 2
Clinical Relevance
Understanding the specific roles of tongue muscles has important implications:
The genioglossus inserts into the entire dorsum of the tongue from the hyoid region posteriorly to the tongue tip anteriorly, with muscle fibers fanning out in a radiating pattern throughout the tongue substance. 3
Genioglossus advancement surgery specifically addresses hypopharyngeal obstruction by advancing the genial tubercle and genioglossus muscle to enlarge the retrolingual airway, though it cannot be recommended as a single procedure for obstructive sleep apnea treatment. 4
The hypoglossal nerve (CN XII) provides somatic motor innervation to all intrinsic and extrinsic tongue muscles (except palatoglossus), making hypoglossal nerve palsy result in dysarthria and tongue deviation to the affected side. 5