Demonstration of primary and secondary muscle fiber architecture of the bovine tongue by diffusion tensor magnetic resonance imaging

The myoarchitecture of the tongue is comprised of a complex array of muscle fiber bundles, which form the structural basis for lingual deformations du ring speech and swallowing. We used magnetic resonance imaging of the water diffusion tensor to display the primary and secondary fiber architectural attributes of the excised bovine tongue. Fiber orientation mapping provides a subdivision of the tongue into its principal intrinsic and extrinsic mus cular components, The anterior tongue consists of a central region of ortho gonally oriented intrinsic fibers surrounded by an axially oriented muscula r sheath. The posterior tongue consists principally of a central region of extrinsic fibers, originating at the inferior surface and projecting in a f an-like manner in the superior, lateral, and posterior directions, and late ral populations of extrinsic fibers directed posterior-inferior and posteri or-superior. Analysis of cross-fiber anisotropy indicates a basic contrast of design between the extrinsic and the intrinsic fibers. Whereas the extri nsic muscles exhibit a uniaxial architecture typical of skeletal muscle, th e intrinsic core muscles, comprised of the verticalis and the transversus m uscles, show strong cross-fiber anisotropy. This pattern is consistent with the theory that the tongue's core functions as a muscular hydrostat in tha t conjoint contraction of the transverse and vertical fibers enable the tis sue to expand at right angles to these fibers. These findings suggest that three-dimensional analysis of diffusion tensor magnetic resonance imaging p rovides a structural basis for understanding the micromechanics of the mamm alian tongue.