Complex fluids flow in complex ways in complex structures. Transport of water and various organic and inorganic molecules in the central nervous system (CNS) are important in a wide range of biological and medical processes [C. Nicholson and S. Hrabětová, “Brain extracellular space: The final frontier of neuroscience,” Biophys. J. 113(10), 2133 (2017)]. However, the exact driving mechanisms are often not known. In this paper, we investigate flows induced by action potentials in an optic nerve as a prototype of the CNS. Different from traditional fluid dynamics problems, flows in biological tissues such as the CNS are coupled with ion transport. It is driven by osmosis created by the concentration gradient of ionic solutions, which in turn influence the transport of ions. Our mathematical model is based on the known structural and biophysical properties of the experimental system used by the Harvard group [R. K. Orkand, J. G. Nicholls, and S. W. Kuffler, “Effect of nerve impulses on the membrane potential of glial cells in the central nervous system of amphibia,” J. Neurophysiol. 29(4), 788 (1966)]. Asymptotic analysis and numerical computation show the significant role of water in convective ion transport. The full model (including water) and the electrodiffusion model (excluding water) are compared in detail to reveal an interesting interplay between water and ion transport. In the full model, convection due to water flow dominates inside the glial domain. This water flow in the glia contributes significantly to the spatial buffering of potassium in the extracellular space. Convection in the extracellular domain does not contribute significantly to spatial buffering. Electrodiffusion is the dominant mechanism for flows confined to the extracellular domain.

中文翻译：

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视神经微循环：流体流动和电扩散

复杂的流体在复杂的结构中以复杂的方式流动。水和各种有机和无机分子在中枢神经系统（CNS）中的运输在许多生物学和医学过程中都很重要[C. Nicholson和S.Hrabětová，“脑细胞外空间：神经科学的最终领域”，Biophys。J. 113（10），2133（2017）]。然而，确切的驱动机制通常是未知的。在本文中，我们研究由视神经动作电位引起的血流，作为中枢神经系统的原型。与传统的流体动力学问题不同，生物组织（例如中枢神经系统）中的流动与离子传输耦合。它是由离子溶液浓度梯度产生的渗透作用驱动的，而渗透作用又影响离子的传输。我们的数学模型基于哈佛小组使用的实验系统的已知结构和生物物理特性[RK Orkand，JG Nicholls和SW Kuffler，“神经冲动对大鼠中枢神经系统神经胶质细胞膜电位的影响”。两栖动物”，J。Neurophysiol。29（4），788（1966）]。渐近分析和数值计算表明水在对流离子迁移中的重要作用。详细比较了完整模型（包括水）和电扩散模型（不包括水），以揭示水与离子传输之间有趣的相互作用。在完整模型中，由于水流引起的对流在胶质域内占主导地位。胶质细胞中的这种水流动显着地促进了钾在细胞外空间中的空间缓冲。细胞外结构域中的对流对空间缓冲没有显着贡献。电扩散是限制在细胞外区域流动的主要机制。