Hylander William L, Wall Christine E, Vinyard Christopher J, Ross Callum, Ravosa Mathew R, Williams Susan H, Johnson Kirk R
Department of Biological Anthropology and Anatomy, Duke University Medical Center, Durham, North Carolina 27710, USA. hylan0012mc.duke.edu
Am J Phys Anthropol. 2005 Sep;128(1):35-56. doi: 10.1002/ajpa.20058.
The major purpose of this study is to analyze anterior and posterior temporalis muscle force recruitment and firing patterns in various anthropoid and strepsirrhine primates. There are two specific goals for this project. First, we test the hypothesis that in addition to transversely directed muscle force, the evolution of symphyseal fusion in primates may also be linked to vertically directed balancing-side muscle force during chewing (Hylander et al. [2000] Am. J. Phys. Anthropol. 112:469-492). Second, we test the hypothesis of whether strepsirrhines retain the hypothesized primitive mammalian condition for the firing of the anterior temporalis, whereas anthropoids have the derived condition (Weijs [1994] Biomechanics of Feeding in Vertebrates; Berlin: Springer-Verlag, p. 282-320). Electromyographic (EMG) activities of the left and right anterior and posterior temporalis muscles were recorded and analyzed in baboons, macaques, owl monkeys, thick-tailed galagos, and ring-tailed lemurs. In addition, as we used the working-side superficial masseter as a reference muscle, we also recorded and analyzed EMG activity of the left and right superficial masseter in these primates. The data for the anterior temporalis provided no support for the hypothesis that symphyseal fusion in primates is linked to vertically directed jaw muscle forces during mastication. Thus, symphyseal fusion in primates is most likely mainly linked to the timing and recruitment of transversely directed forces from the balancing-side deep masseter (Hylander et al. [2000] Am. J. Phys. Anthropol. 112:469-492). In addition, our data demonstrate that the firing patterns for the working- and balancing-side anterior temporalis muscles are near identical in both strepsirrhines and anthropoids. Their working- and balancing-side anterior temporalis muscles fire asynchronously and reach peak activity during the power stroke. Similarly, their working- and balancing-side posterior temporalis muscles also fire asynchronously and reach peak activity during the power stroke. Compared to these strepsirrhines, however, the balancing-side posterior temporalis of anthropoids appears to have a relatively delayed firing pattern. Moreover, based on their smaller W/B ratios, anthropoids demonstrate a relative increase in muscle-force recruitment of the balancing-side posterior temporalis. This in turn suggests that anthropoids may emphasize the duration and magnitude of the power stroke during mastication. This hypothesis, however, requires additional testing. Furthermore, during the latter portion of the power stroke, the late activity of the balancing-side posterior temporalis of anthropoids apparently assists the balancing-side deep masseter in driving the working-side molars through the terminal portion of occlusion.
本研究的主要目的是分析各种类人猿和狐猴型灵长类动物颞肌前后部的力量募集和放电模式。该项目有两个具体目标。第一，我们检验以下假设：除了横向肌肉力量外，灵长类动物耻骨联合融合的进化也可能与咀嚼过程中垂直方向的平衡侧肌肉力量有关（海兰德等人[2000年]《美国体质人类学杂志》112:469 - 492）。第二，我们检验以下假设：狐猴型灵长类动物是否保留了颞肌前部放电的假定原始哺乳动物状态，而类人猿具有衍生状态（魏伊斯[1994年]《脊椎动物摄食的生物力学》；柏林：施普林格出版社，第282 - 320页）。在狒狒、猕猴、夜猴、粗尾婴猴和环尾狐猴中记录并分析了左右颞肌前后部的肌电图（EMG）活动。此外，由于我们将工作侧浅层咬肌用作参考肌肉，我们还记录并分析了这些灵长类动物左右浅层咬肌的EMG活动。颞肌前部的数据不支持灵长类动物耻骨联合融合与咀嚼过程中垂直方向颌部肌肉力量有关的假设。因此，灵长类动物耻骨联合融合最有可能主要与平衡侧深层咬肌横向力量的时间和募集有关（海兰德等人[2000年]《美国体质人类学杂志》112:469 - 492）。此外，我们的数据表明，在狐猴型灵长类动物和类人猿中，工作侧和平衡侧颞肌前部的放电模式几乎相同。它们工作侧和平衡侧的颞肌前部异步放电，并在动力冲程期间达到峰值活动。同样，它们工作侧和平衡侧的颞肌后部也异步放电，并在动力冲程期间达到峰值活动。然而，与这些狐猴型灵长类动物相比，类人猿平衡侧颞肌后部的放电模式似乎相对延迟。此外，基于它们较小的W/B比率，类人猿显示出平衡侧颞肌后部肌肉力量募集的相对增加。这反过来表明，类人猿在咀嚼过程中可能更强调动力冲程的持续时间和幅度。然而，这一假设需要进一步检验。此外，在动力冲程的后期，类人猿平衡侧颞肌后部的后期活动显然有助于平衡侧深层咬肌驱动工作侧磨牙通过咬合的末期。
