Tongue Muscle Response to Neuromuscular Diseases and Specific Pathologies

Abstract

The tongue is the only muscular organ in the craniofacial region and plays fundamental roles in almost all oral motor functions, including drinking, ingestion, chewing, swallowing, respiration, and speech. A number of neuromuscular diseases, such as epilepsy, multiple sclerosis, cerebral palsy, muscular dystrophy, Parkinson's and Huntington's diseases, and myasthenia gravis, signi fi cantly affect tongue motor functions. These negative impacts include reduced or complete loss of control in moving the tongue (tongue displacement) and/or changing the shape of the tongue (tongue deformation), tongue spasm or convulsion, muscle dystonia, and ankyloglossia. Several sensational disorders may also occur due to these neuromuscular diseases, including burning tongue, loss of taste function (ageusia), decreased ability to taste (hypogeusia), and changes in taste (dysgeusia). In recent decades, extensive studies have demonstrated that tongue size, volume, position, and neuromuscular activity, especially in the tongue base, are signi fi cantly implicated in obstructive sleep apnea (OSA), a potential life-threatening disorder of breathing, which affects 2-4% of the adult population (Schwab 2003 ;Schwab et al . 2003 ) .In addition to the complex network of interwoven fi bers and fi ber bundles from four intrinsic and four extrinsic tongue muscles which facilitate complicated and delicate tongue kinematics, the tongue also has a large network of subdividing nerve branches and blood supply. Studies have shown that the hypoglossal nerve alone has more than 50 primary branches innervating tongue musculature (Mu and Sanders 1999 ) . Unlike other body motor organs, the tongue is composed almost entirely of

Alteration of functional loads after tongue volume reduction

“…As we knew, the mechanical effect produced by the tongue during function is mainly derived from its modes of bodily motion and internal deformation. While bodily tongue movement before and after the surgery is not available from the current study, our longitudinal deformation data confirms that at week 1 after the surgery, masticatory deformations decreased in the anterior width and body length, but increased in the posterior widths and thickness significantly, as compared to the baselines (week 0) . At week 2, the reduced deformational capacity in the anterior tongue (width and length) was slightly restored with better regularity of stereotypical chewing cycles than those seen at week 1 .…”

“…While bodily tongue movement before and after the surgery is not available from the current study, our longitudinal deformation data confirms that at week 1 after the surgery, masticatory deformations decreased in the anterior width and body length, but increased in the posterior widths and thickness significantly, as compared to the baselines (week 0) . At week 2, the reduced deformational capacity in the anterior tongue (width and length) was slightly restored with better regularity of stereotypical chewing cycles than those seen at week 1 . However, the increased deformation in the posterior tongue (widths and thickness) diminished as compared to those seen at week 1 .…”

“…This altered tongue kinematics might produce profound influences on its mechanical effects, including the changes of strain pattern and orientation, and the enhancement of strains magnitude. In other word, for the reduction animals, while the decreased bone strains found in our previous acute study might be due to the simple physical loss of tongue mass and post‐surgical complications, the increased bone strain and altered strain pattern/orientation found in the present study are mainly derived from the tissue restructure of the tongue and the changes in its contraction modes in the healed volume‐reduced tongue as demonstrated in the tongue kinematic and histological studies in these same animals .…”

“…At week 2, the reduced deformational capacity in the anterior tongue (width and length) was slightly restored with better regularity of stereotypical chewing cycles than those seen at week 1 . However, the increased deformation in the posterior tongue (widths and thickness) diminished as compared to those seen at week 1 . At week 4, the restoration of anterior tongue deformation continued, but the deformational range in the posterior tongue further decreased and almost returned to those seen at the baseline (week 0) .…”

“…However, the increased deformation in the posterior tongue (widths and thickness) diminished as compared to those seen at week 1 . At week 4, the restoration of anterior tongue deformation continued, but the deformational range in the posterior tongue further decreased and almost returned to those seen at the baseline (week 0) . These time‐course changes in tongue internal deformation clearly indicates that although there is a short‐term loss of deformational capacity in the anterior tongue and a compensatory enhancing deformation in the posterior tongue, these distorted features diminished over time, presented by the restoration of reduced deformation in the anterior tongue and the vanishing of enhanced deformation in the posterior tongue over time.…”