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Comparative Study
. 2007 Aug;52(8):786-96.
doi: 10.1016/j.archoralbio.2007.01.004. Epub 2007 Mar 12.

Roles of intrinsic and extrinsic tongue muscles in feeding: electromyographic study in pigs

Affiliations
Comparative Study

Roles of intrinsic and extrinsic tongue muscles in feeding: electromyographic study in pigs

Mustafa Kayalioglu et al. Arch Oral Biol. 2007 Aug.

Abstract

The performance of tongue muscles in various feeding behaviours is not well defined. This study was undertaken to examine the role of the intrinsic and extrinsic tongue muscles during natural drinking, food ingestion and chewing. Ten 12-week-old Yucatan miniature pigs (5 in each gender) were used. Under anesthesia, fine-wire electrodes were inserted into three intrinsic (verticalis and transversus [V/T]; superior and inferior longitudinalis [SL and IL]) and two extrinsic (genioglossus [GG] and styloglossus [SG]) tongue muscles and two jaw muscles (masseter [MA] and anterior digastricus [DI]). Electromyogram (EMG) and jaw movement were recorded and synchronized when pigs were drinking water, ingesting and chewing food freely. Chewing frequency (CF), onset of activation, burst duration and integrated activity (IEMG) were assessed quantitatively, and EMG activities during drinking and ingestion were examined qualitatively. Results indicate that during chewing, the V/T and GG had one phase of activity starting at early jaw opening, and the V/T activity lasted through late of jaw closing. The SL, IL and SG had double phases with the first starting at jaw opening and the second at late jaw closing phases. The three intrinsic tongue muscles and the SG were active during 35-48% of the chewing cycle. IEMG values of the SL, IL and SG of both sides were significantly greater compared to the other muscles (p<0.05-0.01). Both the SL and the IL showed significantly higher activities in the contralateral than ipsilateral sides (p<0.05). The timing sequences of both extrinsic and intrinsic muscles were similar between ingestion and chewing, but amplitudes of the GG and IL were greatly enhanced and those of the MA and SL were reduced during ingestion. The simultaneous activation of the MA, GG and V/T were seen during drinking, along with major activity in the GG and V/T. These results suggested that the majority of activity in the intrinsic and extrinsic tongue muscles occurred during jaw opening and the occlusal phases of chewing. The activity of the GG and IL played a major role during ingestion, whereas simultaneous activation of jaw, extrinsic and intrinsic tongue muscles and major activity in the GG and V/T occurred during drinking.

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Figures

Fig. 1
Fig. 1
A typical jaw movement tracing (the top) with synchronized masseter EMG activities (bottom two) during chewing. Lines indicate marked events during jaw movement digitization. Solid line: maximal opening; Dashed line: maximal closing; Dotted line: end of power stroke (occlusal) O: jaw opening phase, C: jaw closing phase, P: occlusal (power stroke) phase. The letters (L and R) above the figure indicate chewing sides.
Fig. 2
Fig. 2
Raw EMGs of jaw, tongue extrinsic and intrinsic muscles during chewing. Lines indicate the onset of masseter activation. Arrows show double-phased activity. Single- and double-headed arrows indicate the first and second phases, respectively. Note that of 10 animals, only 2 showed double-phased activity in the ipsilateral digastricus. The letters above EMGs indicate chewing side.
Fig. 3
Fig. 3
Raw EMGs of jaw, tongue extrinsic and intrinsic muscles during food ingestion. Arrows indicate major activity in the genioglossus and inferior logitudinalis.
Fig. 4
Fig. 4
Raw EMGs of jaw, tongue extrinsic and intrinsic muscles during food ingestion. Arrows indicate major activity in the genioglossus and verticalis/transversus.
Fig. 5
Fig. 5
The comparison of activation onsets and burst durations in relation to jaw gape in chewing. Two dotted lines indicate one chewing cycle length, and two solid lines indicate maximal jaw opening and closing. Bar lengths indicate the mean percentages of burst duration and the distances of the bars to left dotted line indicate activation onsets in relation to the start of jaw opening in chewing. Error bars left and right to each histogram bars indicate 1 standard deviation (S.D.) of onset and duration, respectively. Asterisks indicate significant difference between ipsilateral and contralateral sides in the onset (left) and duration (right). Numbers below each muscle name indicate sample size (animal numbers/chewing cycle numbers). *p < 0.05; **p < 0.01; ***p < 0.001.
Fig. 6
Fig. 6
Boxplots of integrated activity values (IEMG) among the recorded muscles during chewing. Upper and lower limits of box represent 75th and 25th percentile, respectively. Horizontal line in each box represents the median. Small circles outside box represent outliers (1.3-3 of box length). The asterisks above the solid lines indicate significant differences between muscles, and asterisks above the boxes indicate the significant differences between ipsilateral and contralateral sides. I: ipsilateral side; C: contralateral side. See Fig. 5 for other symbols.

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