Coordination of cortically induced rhythmic jaw and tongue movements in the rabbit

Abstract

1. Rhythmic movements of the jaw, tongue, and hyoid that were induced by stimulation of the cortical masticatory area (CMA) were recorded cineradiographically in the anesthetized rabbit. Jaw movements were also recorded by a laser position detector. 2. The evoked jaw movements were classified into four types: small circular (type A), large circular (type B), large vertical (type C), and crescent-shaped (type D). Among these, types B and D resembled the jaw movements of the food transport cycle and those of the chewing cycle in a masticatory sequence. 3. Each type of jaw movement was associated with a particular pattern of tongue and hyoid movements. In general, the tongue protruded during jaw opening and retracted during jaw closure. The hyoid generally moved upward and forward during jaw opening but downward and backward during jaw closure. 4. Electromyograms (EMGs) were recorded from jaw muscles [masseter (Ma) and digastric (Di) muscles], extrinsic tongue muscles [styloglossus (Sg) and genioglossus (Gg) muscles], and hyoid muscles [sternohyoid (Sh) and geniohyoid (Gh) muscles] during cortically induced rhythmic jaw and tongue movements (CRJTMs). These muscles were classified into two groups: group 1 was activated mainly in the jaw opening phase, and group 2 was activated mainly in the jaw closing and power phases. The Di, Gg, and Gh were included in the former, and the Ma, Sg, and Sh were included in the latter. 5. The timings of EMG activation to a jaw movement cycle were relatively constant for the muscles of group 1, irrespective of the types of CRJTMs, whereas those for the muscles of group 2 altered considerably with the different types of CRJTMs. 6. Relationships of the integrated muscle activity between the Di and Gg and between the Di and Gh were significant, whereas those between the Ma and Sg and between the Ma and Sh were not. 7. When a small strip of polyurethane form of various degrees of hardness was inserted between the opposing molars during CRJTMs, EMG activity of the muscles of group 2 increased with the hardness of the strip. On the other hand, EMG activities of the muscles of group 1 were less affected by the same intraoral stimuli. 8. Two conclusions were reached: first, physiological properties of the CRJTMs and cortically induced rhythmic movements of the hyoid were essentially similar to those observed in natural mastication. This fictive mastication might thus be regarded as a suitable model for simulating natural mastication.(ABSTRACT TRUNCATED AT 400 WORDS)

Internal Kinematics of the Tongue During Feeding in Pigs

“…While much is known about the gross position or movement direction of the tongue during various feeding behaviors (Thexton et al, 1982(Thexton et al, , 2004Bosma et al, 1990;Liu et al, 1993Liu et al, , 1995Palmer et al, 1997;Hiiemae et al, 2002), the associated shape changes caused by multidimensional expansion or contraction within the tongue have received little attention. As a muscular hydrostat organ, the tongue is incompressible and has constant volume (Kier and Smith, 1985).…”

Modulation of mandibular loading and bite force in mammals during mastication

“…Several studies have shown that increases in food 'hardness' are associated with increases in EMG burst duration (Hidaka et al, 1997;Lavigne et al, 1987;Liu et al, 1993;Lund et al, 1998;Morimoto et al, 1989). On the basis of these EMG data, it might seem reasonable to hypothesize that variation in bite force magnitudes in mammals is significantly correlated with variation in the duration of force generation.…”

“…This hypothesis predicts that variation in strain magnitude will be positively correlated with variation in load time, will not be correlated with strain rate, and will be correlated with increases in chewing duty factor and cycle time. Empirical support for this hypothesis derives from studies demonstrating that increases in hardness of objects placed between the teeth during cortically evoked rhythmic jaw movements (CRJMs) are associated with increases in cycle time (Hidaka et al, 1997;Lavigne et al, 1987;Liu et al, 1998;Liu et al, 1993). Time-modulation of force is also suggested by data showing that when harder foods are chewed there are increases in cycle time, increases in the duration of the slow close or power stroke phase of the chewing cycle, and/or increases in burst durations of jaw adductor muscles (Kakizaki Weijs and Dantuma, 1981;Yamada and Haraguchi, 1995;Yamada and Yamamura, 1996).…”

“…placed between the teeth during cortically evoked rhythmic jaw movements (CRJMs) (Hidaka et al, 1997;Lavigne et al, 1987;Liu et al, 1998;Liu et al, 1993;Plesh et al, 1986). If cycle duration increases with food hardness, why does mandibular loading time not reliably predict mandibular loading magnitude during rhythmic chewing?…”

Supratrigeminal Bilaterally Projecting Neurons Maintain Basal Tone and Enable Bilateral Phasic Activation of Jaw-Closing Muscles

“…7). In response to biting on a hard piece of food, the force of jaw closing increases correspondingly (Liu et al, 1993). It is possible that the excitatory SupV BPNs receive sensory inputs from teeth and other oral cavity afferents, and together with mesencephalic spindle afferents increase activation of jaw-closing motoneurons to facilitate chewing of hard food.…”