Body stiffness and damping depend sensitively on the timing of muscle activation in lampreys
Body stiffness and damping depend sensitively on the timing of muscle activation in lampreys
复制标题
七鳃鳗的身体刚度和阻尼敏感地取决于肌肉激活的时间
DOI：
10.1093/icb/icy042
复制
发表时间：
2018
影响因子：
2.6
通讯作者：
Ankarali, M Mert
中科院分区：
文献类型：
--
作者：
Tytell, Eric D;Carr, Jennifer A;Danos, Nicole;Wagenbach, Christopher;Sullivan, Caitlin M;Kiemel, Tim;Cowan, Noah J;Ankarali, M Mert
与大多数人造机器不同，动物使用灵活的身体和附肢在其世界中移动，这些身体和附肢由于内部肌肉和身体力量以及来自环境的力量而弯曲。鱼类尤其必须应对流体动力，这些动力不仅会阻碍它们的整体游泳运动，而且可能会产生不稳定的流动模式、涡流和湍流，其中许多发生的速度比神经系统的处理速度要快。自然选择是否导致鱼体及其组成组织的机械特性能够对环境扰动做出快速反应？在这里，我们重点研究银七鳃鳗（Ichthyomyzon unicuspis）中孤立的肌肉组织和整个完整身体的机械特性。我们开发了两种修改后的工作循环方案，以确定小扰动对整个身体和孤立的肌肉片段的影响，作为游泳周期内肌肉激活和阶段的函数。首先，我们研究了整个七鳃鳗身体的机械特性如何根据肌肉活动的时间而变化。相对于被动肌肉，肌肉激活可以将有效刚度调节大约两倍，并将有效阻尼调节>10倍，具体取决于激活阶段。接下来，我们对轴向肌肉组织的小部分进行了标准工作循环测试，同时在特定频率下添加低幅度正弦扰动。我们使用基于时间周期系统分析和谐波传递函数（HTF）的新系统识别技术对数据进行建模，并使用所得模型来预测新条件下的肌肉功能。我们发现，肌肉的有效刚度和阻尼在游泳周期中会发生变化，并且激活的时间可以改变峰值刚度和阻尼的大小和时间。此外，孤立肌肉的反应是高度非线性且依赖于长度的，但身体的反应则更为线性。我们应用实验产生的 HTF 来探索成对拮抗肌的效果。结果表明，当肌肉作为拮抗剂相互对抗时，组合系统的非线性比单独的任何一个肌肉片段都要弱。总之，这些结果开始提供对激活时间如何调整肌肉的机械响应特性的综合理解，使鱼类能够在复杂且不可预测的环境中有效地游泳。
Unlike most manmade machines, animals move through their world using flexible bodies and appendages, which bend due to internal muscle and body forces, and also due to forces from the environment. Fishes in particular must cope with fluid dynamic forces that not only resist their overall swimming movements but also may have unsteady flow patterns, vortices, and turbulence, many of which occur more rapidly than what the nervous system can process. Has natural selection led to mechanical properties of fish bodies and their component tissues that can respond very quickly to environmental perturbations? Here, we focus on the mechanical properties of isolated muscle tissue and of the entire intact body in the silver lamprey,Ichthyomyzon unicuspis.We developed two modified work loop protocols to determine the effect of small perturbations on the whole body and on isolated segments of muscle as a function of muscle activation and phase within the swimming cycle. First, we examined how the mechanical properties of the whole lamprey body change depending on the timing of muscle activity. Relative to passive muscle, muscle activation can modulate the effective stiffness by about two-fold and modulate the effective damping by >10-fold depending on the activation phase. Next, we performed a standard work loop test on small sections of axial musculature while adding low-amplitude sinusoidal perturbations at specific frequencies. We modeled the data using a new system identification technique based on time-periodic system analysis and harmonic transfer functions (HTFs) and used the resulting models to predict muscle function under novel conditions. We found that the effective stiffness and damping of muscle varies during the swimming cycle, and that the timing of activation can alter both the magnitude and timing of peak stiffness and damping. Moreover, the response of the isolated muscle was highly nonlinear and length dependent, but the body’s response was much more linear. We applied the resulting HTFs from our experiments to explore the effect of pairs of antagonistic muscles. The results suggest that when muscles work against each other as antagonists, the combined system has weaker nonlinearities than either muscle segment alone. Together, these results begin to provide an integrative understanding of how activation timing can tune the mechanical response properties of muscles, enabling fish to swim effectively in their complex and unpredictable environment.