JB Palmer, NJ Rudin, G Lara, and AW Crompton. 1992. “
Coordination of mastication and swallowing.” DysphagiaDysphagia, 7, Pp. 187-200.
AbstractThe coordination of mastication, oral transport, and swallowing was examined during intake of solids and liquids in four normal subjects. Videofluorography (VFG) and electromyography (EMG) were recorded simultaneously while subjects consumed barium-impregnated foods. Intramuscular electrodes were inserted in the masseter, suprahyoid, and infrahyoid muscles. Ninety-four swallows were analyzed frame-by-frame for timing of bolus transport, swallowing, and phases of the masticatory gape cycle. Barium entered the pharynx a mean of 1.1 s (range -0.3 to 6.4 s) before swallow onset. This interval varied significantly among foods and was shortest for liquids. A bolus of food reached the valleculae prior to swallow onset in 37% of sequences, but most of the food was in the oral cavity at the onset of swallowing. Nearly all swallows started during the intercuspal (minimum gape) phase of the masticatory cycle. Selected sequences were analyzed further by computer, using an analog-to-digital convertor (for EMG) and frame grabber (for VFG). When subjects chewed solid food, there were loosley linked cycles of jaw and hyoid motion. A preswallow bolus of chewed food was transported from the oral cavity to the oropharynx by protraction (movement forward and upward) of the tongue and hyoid bone. The tongue compressed the food against the palate and squeezed a portion into the pharynx one or more cycles prior to swallowing. This protraction was produced by contraction of the geniohyoid and anterior digastric muscles, and occurred during the intercuspal (minimum gape) and opening phases of the masticatory cycle. The mechanism of preswallow transport was highly similar to the oral phase of swallowing. Alternation of jaw adductor and abductor activity during mastication provided a framework for integration of chewing, transport, and swallowing.
RZ German, AW Crompton, LC Levitch, and AJ Thexton. 1992. “
The mechanism of suckling in two species of infant mammal: miniature pigs and long-tailed macaques.” J Exp ZoolJournal of Experimental Zoology, 261, Pp. 322-30.
AbstractSuckling is the form of feeding unique to infant mammals. The mechanism used by infant mammals to withdraw liquid from the nipple is the subject of considerable debate. Suckling has been examined in two species of infant mammals: miniature pigs and long-tailed macaques. In both species radio-opaque markers were inserted into the tongue and jaws; the movements of the jaw and tongue (and also of specific regions within the tongue) plus the movement of milk containing barium were studied by high-speed cineradiography (100 and 150 frames/sec). In the case of macaques, simultaneous pressure transducer recordings were also made. In both species, liquid moved out of the nipple as the intraoral space was expanded by a combination of tongue movement (negative pressure pumping) coupled with jaw opening. There was no evidence for expression (positive pressure on the nipple) in either species, strongly supporting the view that a suction mechanism is responsible for acquisition of milk from the nipple. Subsequent intraoral transport was different in the two species. The pigs used a second pump mechanism at the base of the tongue to transport liquid through the pillars of the fauces into the valleculae. The monkeys used a "squeeze-back" mechanism similar to the transport mechanism documented for adult macaques. Further work with other species can test our tentative hypothesis that all mammals use a negative pressure suction for acquisition, but, as is true for adult mammals, infants may use different transport mechanisms to form and move the bolus.
WL Hylander, KR Johnson, and AW Crompton. 1992. “
Muscle force recruitment and biomechanical modeling: an analysis of masseter muscle function during mastication in Macaca fascicularis.” Am J Phys AnthropolAmerican Journal Physical Anthropology, 88, Pp. 365-87.
AbstractThe main purpose of this study is to test the hypothesis that as subjects chew with increasing levels of force, the ratio of the working- to balancing-side jaw-muscle force (W/B) decreases and begins to approach 1.0. We did this by analyzing relative masseter force in Macaca fascicularis using both strain gage and surface electromyographic (EMG) techniques. In addition, we also analyzed: 1) the relationship between jaw position using cineradiographic techniques and relative masseter force, 2) the timing differences between relative masseter force from the working and balancing sides, and 3) the loading and unloading characteristics of the masseter muscle. Our findings indicate that when macaques increase the amount of overall masticatory force during chewing, the W/B ratio for masseter force frequently (but not always) decreases and begins to approach 1.0. Therefore, our working hypothesis is not completely supported because the W/B ratio does not decrease with increasing levels of force in all subjects. The data also demonstrate timing differences in masseter force. During apple-skin mastication, the average peak masseter force on the working side occurs immediately at or slightly after the initial occurrence of maximum intercuspation, whereas the average peak masseter force on the balancing side occurs well before maximum intercuspation. On average, we found that peak force from the balancing-side masseter precedes the working-side masseter by about 26 msec. The greater the asynchrony between working- and balancing-side masseter force, the greater the difference in the relative magnitude of these forces. For example, in the subject with the greatest asynchrony, the balancing-side masseter had already fallen to about one-half of peak force when the working-side masseter reached peak force. Our data also indicate that the loading and unloading characteristics of the masseter differ between the working and balancing sides. Loading (from 50 to 100% of peak force) and unloading (from 100 to 50% of peak force) for the balancing-side masseter tends to be rather symmetrical. In contrast, the working-side masseter takes much longer to load from 50 to 100% of peak force than it does to unload from 100 to 50% of peak force. Finally, it takes on average about 35 msec for the working-side zygoma and 42 msec for the balancing-side zygoma to unload from 100 to 50% of peak force during apple-skin mastication, indicating that the unloading characteristics of the macaque masseter during mastication closely approximates its relaxation characteristics (as determined by muscle stimulation).
