Cell crawling requires the generation of intracellular forces by the cytoskeleton and their transmission to an extracellular substrate through specific adhesion molecules. Crawling cells show many features of excitable systems, such as spontaneous symmetry breaking and crawling in the absence of external cues, and periodic and propagating waves of activity. Mechanical instabilities in the active cytoskeleton network and feedback loops in the biochemical network of activators and repressors of cytoskeleton dynamics have been invoked to explain these dynamical features. Here, I show that the interplay between the dynamics of cell–substrate adhesion and linear cellular mechanics is sufficient to reproduce many nonlinear dynamical patterns observed in spreading and crawling cells. Using an analytical formalism of the molecular clutch model of cell adhesion, regulated by local mechanical forces, I show that cellular traction forces exhibit stick–slip dynamics resulting in periodic waves of protrusion/retraction and propagating waves along the cell edge. This can explain spontaneous symmetry breaking and polarization of spreading cells, leading to steady crawling or bipedal motion, and bistability, where persistent cell motion requires a sufficiently strong transient external stimulus. The model also highlights the role of membrane tension in providing the long-range mechanical communication across the cell required for symmetry breaking.

细胞爬行需要通过细胞骨架产生细胞内力，并通过特定的粘附分子将其传递至细胞外基质。爬行细胞显示出兴奋性系统的许多特征，例如在没有外部提示的情况下自发对称破裂和爬行，以及周期性和传播性的活动波。激活细胞骨架网络中的机械不稳定性以及细胞骨架动力学的激活剂和阻遏物的生化网络中的反馈环已被用来解释这些动力学特征。在这里，我表明细胞-基质粘附动力学与线性细胞力学之间的相互作用足以再现在扩散和爬行细胞中观察到的许多非线性动力学模式。使用由局部机械力调节的细胞粘附分子离合模型的解析形式，我表明细胞牵引力表现出粘滑运动，从而导致沿细胞边缘的周期性的突出/收缩和传播波。这可以解释自发的对称性破坏和扩散细胞的极化，导致稳定的爬行或两足运动，以及双稳态，其中持续的细胞运动需要足够强的瞬态外部刺激。该模型还强调了膜张力在提供对称断裂所需的整个细胞的长距离机械通讯中的作用。我证明细胞的牵引力表现出粘滑运动，从而导致周期性的突起/收缩波和沿细胞边缘的传播波。这可以解释自发的对称性破坏和扩散细胞的极化，导致稳定的爬行或两足运动，以及双稳态，其中持续的细胞运动需要足够强的瞬态外部刺激。该模型还强调了膜张力在提供对称断裂所需的整个细胞的长距离机械通讯中的作用。我证明细胞的牵引力表现出粘滑运动，从而导致周期性的突起/收缩波和沿细胞边缘的传播波。这可以解释自发的对称性破坏和扩散细胞的极化，导致稳定的爬行或两足运动，以及双稳态，其中持续的细胞运动需要足够强的瞬态外部刺激。该模型还强调了膜张力在提供对称断裂所需的整个细胞的长距离机械通讯中的作用。