Department of Physical Therapy, Duquesne University, Pittsburgh, Pennsylvania, USA.
Undergraduate Pre-Medical and Health Professions Program, Duquesne University, Pittsburgh, Pennsylvania, USA.
Anat Rec (Hoboken). 2023 Oct;306(10):2562-2571. doi: 10.1002/ar.25172. Epub 2023 Feb 17.
Muscle spindles are sensory receptors in skeletal muscle that provide information on muscle length and velocity of contraction. Previous studies noted that facial muscles lack muscle spindles, but recent reports indicate that the human platysma muscle and "buccal" muscles contain spindles. Mammalian facial muscles are active in social communication, vibrissa movement, and vocalizations, including human speech. Given these functions, we hypothesized that facial muscles contain muscle spindles, and we predicted that humans would have the greatest number, given the role our lips play in speech. We examined previously sectioned and stained (with H&E and trichrome stains) orbicularis oris (upper fibers) and zygomaticus (major) muscles across a broad phylogenetic range of mammalian species, spanning a wide distribution of body size and ecological niche, to assess the presence of muscle spindles. We also stained several sections with Sirius red to highlight the muscle spindle capsule. Our results indicate that mammalian facial muscles contain muscle spindles, supporting our hypothesis. Contrary to our prediction, though, humans (and other primates) had the lowest number of muscle spindles. We instead found that the carnivoran sample and the horse sample had the greatest number of spindles. Larger body size and nocturnality were also associated with a greater number of spindles. These results must be viewed with caution, though, as our sample size was small and there are critical mammalian taxa missing. Future work should use an expanded phylogenetic range of mammalian species to ascertain the role that phylogeny plays in muscle spindle presence and count.
肌梭是骨骼肌中的感觉受体，提供关于肌肉长度和收缩速度的信息。以前的研究指出面部肌肉缺乏肌梭，但最近的报告表明，人类的颈阔肌和“颊”肌含有梭。哺乳动物的面部肌肉在社交交流、触须运动和发声中活跃，包括人类的言语。考虑到这些功能，我们假设面部肌肉含有肌梭，并且我们预测人类会拥有最多的肌梭，因为我们的嘴唇在言语中起着重要的作用。我们检查了广泛的哺乳动物物种的口轮匝肌（上纤维）和颧大肌的先前切片和染色（用 H&E 和三色染色），跨越了身体大小和生态位的广泛分布，以评估肌梭的存在。我们还用 Sirius red 染色了几个切片，以突出肌梭囊。我们的结果表明，哺乳动物的面部肌肉含有肌梭，支持我们的假设。然而，与我们的预测相反，人类（和其他灵长类动物）拥有的肌梭数量最少。相反，我们发现食肉目动物样本和马样本拥有最多的梭。更大的体型和夜间活动也与更多的梭有关。然而，必须谨慎看待这些结果，因为我们的样本量很小，并且有一些关键的哺乳动物类群缺失。未来的工作应该使用扩展的哺乳动物物种的系统发育范围，以确定系统发育在肌梭存在和数量上的作用。
