Moon BR, Gans C
Department of Biology, The University of Michigan, Ann Arbor, MI 48109, USA and Department of Zoology, The University of Texas, Austin, TX 78746, USA.
J Exp Biol. 1998 Oct;201 (Pt 19):2669-84. doi: 10.1242/jeb.201.19.2669.
Previous studies have addressed the physical principles and muscular activity patterns underlying terrestrial lateral undulation in snakes, but not the mechanism by which muscular activity produces curvature and propulsion. In this study, we used synchronized electromyography and videography to examine the muscular basis and propulsive mechanism of terrestrial lateral undulation in gopher snakes Pituophis melanoleucus affinis. Specifically, we used patch electrodes to record from the semispinalis, longissimus dorsi and iliocostalis muscles in snakes pushing against one or more pegs. Axial bends propagate posteriorly along the body and contact the pegs at or immediately posterior to an inflection of curvature, which then reverses anterior to the peg. The vertebral column bends broadly around a peg, whereas the body wall bends sharply and asymmetrically around the anterior surface of the peg. The epaxial muscles are always active contralateral to the point of contact with a peg; they are activated slightly before or at the point of maximal convexity and deactivated variably between the inflection point and the point of maximal concavity. This pattern is consistent with muscular shortening and the production of axial bends, although variability in the pattern indicates that other muscles may affect the mechanics of the epaxial muscles. The kinematic and motor patterns in snakes crawling against experimentally increased drag indicated that forces are produced largely by muscles that are active in the axial bend around each peg, rather than by distant muscles from which the forces might be transmitted by connective tissues. At each point of force exertion, the propulsive mechanism of terrestrial lateral undulation may be modeled as a type of cam-follower, in which continuous bending of the trunk around the peg produces translation of the snake.
以往的研究探讨了蛇类陆地侧向波动背后的物理原理和肌肉活动模式，但未涉及肌肉活动产生弯曲和推进力的机制。在本研究中，我们使用同步肌电图和摄像技术来研究地鼠蛇（Pituophis melanoleucus affinis）陆地侧向波动的肌肉基础和推进机制。具体而言，我们使用贴片电极记录蛇在推挤一个或多个木桩时，其半棘肌、背最长肌和髂肋肌的活动。轴向弯曲沿身体向后传播，并在曲率拐点处或紧接其后与木桩接触，然后在木桩前方反转。脊柱围绕木桩大幅弯曲，而体壁围绕木桩前表面急剧且不对称地弯曲。轴上肌肉总是在与木桩接触点的对侧活跃；它们在最大凸度点之前或之时被激活，并在拐点和最大凹度点之间以不同方式失活。这种模式与肌肉缩短和轴向弯曲的产生一致，尽管模式的变化表明其他肌肉可能会影响轴上肌肉的力学。在实验性增加阻力的情况下爬行的蛇的运动学和运动模式表明，力主要由围绕每个木桩的轴向弯曲中活跃的肌肉产生，而不是由结缔组织可能传递力的远处肌肉产生。在每个施力点，陆地侧向波动的推进机制可被模拟为一种凸轮从动件，其中躯干围绕木桩的持续弯曲产生蛇的平移。
