Symphyseal fusion and jaw-adductor muscle force: An EMG study
Symphyseal fusion and jaw-adductor muscle force: An EMG study
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DOI：
10.1002/1096-8644(200008)112:4
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发表时间：
2000-08-01
影响因子：
2.8
通讯作者：
Johnson, KR
中科院分区：
文献类型：
--
作者：
Hylander, WL;Ravosa, MJ;Johnson, KR
本研究的目的是测试各种假设的平衡侧颌骨肌肉招聘模式在咀嚼，主要集中在测试的假设，即联合融合在下颌骨主要是由于垂直和/或横向的颌骨肌肉力量。此外，由于平衡侧深咬肌已被证明在猕猴下颌联合的wishbone中发挥重要作用，我们测试。具有高度移动的下颌骨联合的灵长类动物没有表现出导致下颌骨叉骨的平衡侧深咬肌放电模式的假设。最后，我们还测试的假设，即平衡侧肌肉招聘模式是重要的异速生长的限制与不断增加的身体尺寸的演变。记录并分析了狒狒、猕猴、猫头鹰猴和厚尾斑羚的左、右浅表和深层咬肌的肌电图（EMG）活动。选择咬肌进行分析是因为在额面投影中，其浅表部分主要在垂直（背腹）方向上施加力，而其深层部分在横向方向上具有相对较大的力分量。联合融合-肌肉补充假说预测，与类人猿不同的是，加拉戈斯的咬合力来自其平衡侧颌骨肌肉的贡献相对较小。因此，与加拉戈斯相比，类人猿从平衡侧肌肉中吸收了更大比例的力量。如果这是真的，这意味着在有力的咀嚼过程中，Galagos应该具有相对较大的工作侧/平衡侧（W/B）EMG比率，而Ragos应该具有相对较小的W/B比率。肌电图数据表明，加拉戈斯确实有最大的平均W/B比的浅表和深咬肌（2.2和4.4，分别）。在狒狒中，浅咬肌和深咬肌的平均W/B比值为1.9和1.0，猕猴为1.4和1.0，猫头鹰猴的两个值均为1.4。然而，在这些比率中，厚尾加拉戈斯和仙女座流星雨之间唯一的显著差异是与深咬肌有关的差异。此外，咬肌放电模式的分析表明，而狒狒，猕猴和猫头鹰猴表现出深咬肌放电模式与猕猴下颌骨联合wishboning，加拉戈斯不表现出这种放电模式。异速生长约束肌肉招募假说预测，较大的灵长类动物必须招募相对大量的平衡侧肌肉力量，以发展等量的咬合力。这在操作上意味着，在有力的咀嚼，W/B肌电比的浅表和深咬肌应呈负相关的身体大小。我们的分析清楚地驳斥了这一假设。如前所述，厚尾加拉戈斯的表层咬肌和深层咬肌的平均W/B比值最大，而不是像异速生长约束假说所预测的那样，在猫头鹰猴中最大，猫头鹰猴是一种体型比厚尾加拉戈斯小的类人猿。我们的分析还表明，猫头鹰猴的W/B比值很小，与体型大得多的狒狒和猕猴更相似。因此，W/B EMG比值和肌肉放电模式数据的分析都支持这一假设，即联合融合和横向指向的肌肉力量在功能上是联系在一起的，这反过来又支持了这一假设，即联合融合的进化在咀嚼肌是一种适应，以加强联合，以对抗增加wishboning应力在有力的单侧咀嚼。相反，W/B EMG比值没有（或可以说是微弱的）支持联合融合和垂直定向肌肉力量在功能上相关的假设，并且数据清楚地反驳了平衡侧下颌肌肉招募模式受与身体尺寸增加的进化相关的异速生长因素影响的假设。(C)2000 Wiley-Liss，Inc.
The purpose of this study is to test various hypotheses about balancing-side jaw muscle recruitment patterns during mastication, with a major focus on testing the hypothesis that symphyseal fusion in anthropoids is due mainly to vertically- and/or transversely-directed jaw muscle forces. Furthermore, as the balancing-side deep masseter has been shown to play an important role in wishboning of the macaque mandibular symphysis, we test. the hypothesis that primates possessing a highly mobile mandibular symphysis do not exhibit the balancing-side deep masseter firing pattern that causes wishboning of the anthropoid mandible. Finally, we also test the hypothesis that balancing-side muscle recruitment patterns are importantly related to allometric constraints associated with the evolution of increasing body size. Electromyographic (EMG) activity of the left and right superficial and deep masseters were recorded and analyzed in baboons, macaques, owl monkeys, and thick-tailed galagos, The masseter was chosen for analysis because in the frontal projection its superficial portion exerts force primarily in the vertical (dorsoventral) direction, whereas its deep portion has a relatively larger component of force in the transverse direction. The symphyseal fusion-muscle recruitment hypothesis predicts that unlike anthropoids, galagos develop bite force with relatively little contribution from their balancing-side jaw muscles. Thus, compared to galagos, anthropoids recruit a larger percentage of force from their balancing-side muscles. If true, this means that during forceful mastication, galagos should have working-side/balancing-side (W/B) EMG ratios that are relatively large, whereas anthropoids should have W/B ratios that are relatively small. The EMG data indicate that galagos do indeed have the largest average W/B ratios for both the superficial and deep masseters (2.2 and 4.4, respectively). Among the anthropoids, the average W/B ratios for the superficial and deep masseters are 1.9 and 1.0 for baboons, 1.4 and 1.0 for macaques, and both values are 1.4 for owl monkeys. Of these ratios, however, the only significant difference between thick-tailed galagos and anthropoids are those associated with the deep masseter. Furthermore, the analysis of masseter firing patterns indicates that whereas baboons, macaques and owl monkeys exhibit the deep masseter firing pattern associated with wishboning of the macaque mandibular symphysis, galagos do not exhibit this firing pattern. The allometric constraint-muscle recruitment hypothesis predicts that larger primates must recruit relatively larger amounts of balancing-side muscle force so as to develop equivalent amounts of bite force. Operationally this means that during forceful mastication, the W/B EMG ratios for the superficial and deep masseters should be negatively correlated with body size. Our analysis clearly refutes this hypothesis. As already noted, the average W/B ratios for both the superficial and deep masseter are largest in thick-tailed galagos, and not, as predicted by the allometric constraint hypothesis, in owl monkeys, an anthropoid whose body size is smaller than that of thick-tailed galagos. Our analysis also indicates that owl monkeys have W/B ratios that are small and more similar to those of the much larger-sized baboons and macaques. Thus, both the analysis of the W/B EMG ratios and the muscle firing pattern data support the hypothesis that symphyseal fusion and transversely-directed muscle force in anthropoids are functionally linked.This in turn supports the hypothesis that the evolution of symphyseal fusion in anthropoids is an adaptation to strengthen the symphysis so as to counter increased wishboning stress during forceful unilateral mastication. In contrast, the W/B EMG ratios provide no (or arguably weak) support for the hypothesis that symphyseal fusion and vertically-directed muscle force are functionally linked, and the data clearly refute the hypothesis that balancing-side jaw-muscle recruitment patterns are influenced by allometric factors associated with the evolution of increasing body size. (C) 2000 Wiley-Liss, Inc.