Craniofacial Muscles

14 Tongue Muscle Response to Neuromuscular Diseases and Speci fi c Pathologies
249
Fig. 14.6 Fluorescent marks of jaw ( a ) and tongue tip ( b ), and tracings (digitized) of jaw and
tongue movement during chewing ( c )
muscles. Ingestion function is characterized by early expansion of anterior width
prior to the occlusal phase and strong associations between tongue deformation and
muscle activity. During drinking, the durations of tongue widening and lengthening
are signi fi cantly shortened whereas these are signi fi cantly prolonged during the
opening and closing phases of jaw movement. Anterior widening is predominant in
the opening whereas posterior thickening lasts from early jaw opening through late
closing. This speci fi c pattern of dimensional changes suggests that the tongue
stretches in width fi rst before jaw opening, then elongates and thickens to form a
central groove during drinking. This is an ideal shape to exert the mechanism of
suction, because no lapping and licking for liquid feeding is reported in pigs and
most of ungulates (Shcherbatyy and Liu 2007 ; Herring and Scapino 1973 ; Thexton
et al . 1998 ) . Interestingly, intrinsic tongue muscles do not have more or stronger
correlations with tongue deformation than do extrinsic tongue muscles. The time
and correlation analyses further found that the initiation of tongue dimensional
increase does not correspond with the activation of tongue muscles simultaneously.
A better coupling between tongue deformations and tongue muscle activations
exists in the sagittal (lengthening and thickening) than the transverse (widening)
planes of the tongue. Furthermore, expansion magnitudes of tongue deformation do