Tongue Muscle Anatomy: Architecture and Function

The tongue is composed entirely of soft tissue: muscle, fat, and connective tissue. This unusual composition and the tongue’s 3D muscle fiber orientation result in many degrees of freedom. The lack of bones and cartilage means that muscle shortening creates deformations, particularly local deformations, as the tongue moves into and out of speech gestures. The tongue is also surrounded by the hard structures of the oral cavity, which both constrain its motion and support the rapid small deformations that create speech sounds. Anatomical descriptors and categories of tongue muscles do not correlate with tongue function as speech movements use finely controlled co-contractions of antagonist muscles to move the oral structures during speech. Tongue muscle volume indicates that four muscles, the genioglossus, verticalis, transversus, and superior longitudinal, occupy the bulk of the tongue. They also comprise a functional muscle grouping that can shorten the tongue in the x, y, and z directions. Various 3D muscle shortening patterns produce large- or small-scale deformations in all directions of motion. The interdigitation of the tongue’s muscles is advantageous in allowing co-contraction of antagonist muscles and providing nimble deformational changes to move the tongue toward and away from any position.