Department of Biology, University of Akron, Akron, Ohio, USA.
Department of Kinesiology, Biomechanics Laboratory, Pennsylvania State University, Pennsylvania, USA.
J Morphol. 2023 Jun;284(6):e21591. doi: 10.1002/jmor.21591.
Muscles spanning multiple joints play important functional roles in a wide range of systems across tetrapods; however, their fundamental mechanics are poorly understood, particularly the consequences of anatomical position on mechanical advantage. Snakes provide an excellent study system for advancing this topic. They rely on the axial muscles for many activities, including striking, constriction, defensive displays, and locomotion. Moreover, those muscles span from one or a few vertebrae to over 30, and anatomy varies among muscles and among species. We characterized the anatomy of major epaxial muscles in a size series of corn snakes (Pantherophis guttatus) using diceCT scans, and then took several approaches to calculating contributions of each muscle to force and motion generated during body bending, starting from a highly simplistic model and moving to increasingly complex and realistic models. Only the most realistic model yielded equations that included the consequence of muscle span on torque-displacement trade-offs, as well as resolving ambiguities that arose from simpler models. We also tested whether muscle cross-sectional areas or lever arms (total magnitude or pitch/yaw/roll components) were related to snake mass, longitudinal body region (anterior, middle, posterior), and/or muscle group (semispinalis-spinalis, multifidus, longissimus dorsi, iliocostalis, and levator costae). Muscle cross-sectional areas generally scaled with positive allometry, and most lever arms did not depart significantly from geometric similarity (isometry). The levator costae had lower cross-sectional area than the four epaxial muscles, which did not differ significantly from each other in cross-sectional area. Lever arm total magnitudes and components differed among muscles. We found some evidence for regional variation, indicating that functional regionalization merits further investigation. Our results contribute to knowledge of snake muscles specifically and multiarticular muscle systems generally, providing a foundation for future comparisons across species and bioinspired multiarticular systems.
跨越多个关节的肌肉在四足动物的多个系统中发挥着重要的功能作用；然而，它们的基本力学特性还了解甚少，特别是解剖位置对机械优势的影响。蛇类为推进这一主题提供了一个极好的研究系统。它们依靠轴上肌肉来完成许多活动，包括攻击、缠绕、防御展示和运动。此外，这些肌肉从一个或几个椎骨跨越到 30 多个椎骨，而且肌肉之间和物种之间的解剖结构也有所不同。我们使用 DiceCT 扫描对玉米蛇（ Pantherophis guttatus ）的一系列大小系列中的主要轴上肌肉的解剖结构进行了描述，然后采用了几种方法来计算在身体弯曲过程中每个肌肉对产生的力和运动的贡献，从一个高度简化的模型开始，逐渐过渡到越来越复杂和现实的模型。只有最现实的模型才能得出包括肌肉跨度对扭矩-位移权衡的影响的方程，以及解决简单模型引起的歧义。我们还测试了肌肉横截面积或杠杆臂（总幅度或俯仰/偏航/滚转分量）是否与蛇的质量、身体的纵向区域（前、中、后）和/或肌肉群（半棘肌-棘肌、多裂肌、最长肌、髂肋肌和肋提肌）有关。肌肉横截面积通常呈正异速生长，大多数杠杆臂与几何相似性（等距）没有显著差异。肋提肌的横截面积小于四个轴上肌肉，它们的横截面积彼此之间没有显著差异。杠杆臂的总幅度和分量在肌肉之间有所不同。我们发现了一些区域变化的证据，表明功能区域化值得进一步研究。我们的研究结果特别有助于了解蛇类肌肉，也有助于了解多关节肌肉系统，为未来在不同物种和仿生多关节系统之间进行比较提供了基础。
