Chemical and mechanical waves on the cortex of fertilized egg cells: a bioexcitability effect

We analyse a mathematical model in order to describe the propagation of chemical and mechanical waves through the cortex of fertilized egg cells. The model is described by a partial differential equation of the reaction-diffusion kind. This model was formulated by Oster and Odell and its mechanism concerns a condition of excitability of the egg perturbed by fertilization. During this excitability stage one observes the development of a calcium wave which produces contraction and expansion waves in the cytogel. In particular, we consider the behaviour of ascidian eggs after fertilization, emphasizing that the model utilized is suitable to describe the first cortical movements of such eggs. Moreover, we suppose a new "excitability" state of these eggs, after the first ooplasmic segregation. This excitability state is located in the vegetal pole. Finally, we study the mechanical effects caused by a perturbation, which is induced in such vegetal region by increasing the calcium concentration in the culture medium.