鱼类的侧线机械感受系统和仿生学等应用研究

Structure and function of the mechanosensory lateral line system in fish and biomimetic

鱼类和水生两栖类(或幼体),具有特殊的侧线机械感受系统,以感受和分析周围水流微小的时空动态变异,提供鱼体即时的位向和环境水动态信息,助其判断水流属性,完成摄食、避敌、生殖、集群、导航和通讯等复杂行为.侧线机械感受的外周感觉器官主要为两类"神经丘":感受流体加速度(或压力差)和平行于体轴的流向信息,一般是位于体表侧线管道中的"管道神经丘";感受流体速度和垂直于体轴的流向信息,位于鱼体表面的"表面神经丘".两者都由感觉毛细胞和包裹的胶质顶组成.当接触流体的振动波时,胶质顶带动其内部的纤毛束发生定向摆动和偏转,打开毛细胞膜的离子通道,改变细胞的内外电位差,将流体机械信息转换成神经电信号传入.两类神经丘的大小、形状和排列方位(互成90°)不同,并由各自的神经支配.神经丘数目繁多,以特定的模式遍布鱼表,全方位地收集各部位不同瞬间的水动力变化信息,并由专一的侧线传入神经分支至中枢神经各级侧线中心,系统地综合分析.侧线感受器结构的精致程度和侧线系统在鱼体分布空间模式的复杂性,是依鱼的种类(系统进化地位)、水流生境及特殊行为等多方面需求形成.该系统已吸引了科学家近百年的研究,在物种间表观形态和生态行为多样性等,尤其是功能形态和神经电生理学方面,颇有进展.近年来,运用数学、物理、计算科学和纳米技术等多学科交叉研究,正起步开拓其仿生学应用.为进一步推动对侧线生物学和水动力机械感受器模式及其智能仿生学交叉研究领域的发展,本文以鱼类侧线研究的新发现和认识为基础,结合近年来有关侧线系统的研究文献,对侧线机械感受器的结构机理、发育模式、神经功能特性以及仿生学研究的进展与展望等方面进行综述.

As an adaptation to their environment, fishes and some aquatic amphibians have developed a hydrodynamic receptor system, the lateral line mechanosensory system, which enables them to detect minute water motion, and provide information that can apply for feeding, avoidance, schooling, navigation, and intraspecific communication. This system consists of individual sensory receptors, neuromasts, that either lie within lateral line canals along the body （canal neuromasts, CNM） or occur freestanding on the surface of the skin （superficial neuromasts, SNM）. These CNM and SNM act as acceleration （higher frequency response, 60-120 Hz） or velocity receptors （lower frequency response, 20-60 Hz）, respectively, which can also provide the signal location and fluidic direction to the central nervous system （CNS）. The neuromast consists of discrete clusters of sensory hair cells, support cells and mantle cells. On the apical of hair cell, a bundle of several stereocilia and one kinocilium that protrudes from of the hair cell into a gelatinous cupula. The cupula covers entire neuromast apical and connects the ciliary bundles with surrounding water. Deflection of the cupula induces the directional movement of the hair bundles that results in opening or closing of the transduction channels on the kinocilium, affecting the release of neurotransmitter that conveys the hair cell＇s relative excitation to the afferent neuron （in the lateral line ganglion）, then, travels to the target areas in the CNS. Between CNM and SNM, there are several morphological differences such as diameter of sensory epithelium, number of hair cells, orientation of axis, and peripheral innervation pattern. They also demonstrate with different biomechanical properties in detecting different types of hydrodynamic signals and play different roles in responding to the various water motion patterns （including micro fluid）. All the peripheral information that is integrated at different levels of the CNS centers before guiding the proper behavior of fish. The CNM appears to provide information about fine spatial details that lead to the ability of fish to segregate the fine turbulence signal in near field while towards discrete sources or under rapidly changing water motions surrounding. SNM appears to provide peripheral spatial information of large-scale stimuli, such as rheotaxis to slow motion currents. As a delicate hydrodynamic detector system, a well functioned lateral line system that only consists of two types of peripheral receptor plus their architectural design of arrangement and canal pattern modifications that is far advanced than, up to date, any of the man-made underwater detector in the world. Even more, the system provides a high efficient computing model that is from the peripheral innervation pattern designed for major collection of temporal and spatial hydrodynamic information, the integration of data processing structure, and to the action assignment in the CNS. The mechanosensory lateral line system in fish is starting attracted by research approaches in biomimetic, mathematics, physical and computing sciences, in addition to the biology and neurosciences. The participating of integrative study on the lateral line system, that is not only help developing of new applications but also enhanced biological understand of the system. The biologists have been speculated the function of the CNM, the co-relationship of the canal morphology and fish habits over decades. Until recently, the mathematic model and the device of artificial lateral line receptor established by Klein and Bleckmann （2015）, demonstrate that ＂it is possible to change the transfer function of an artificial line by changing its canal shape, dimensions and pore pattern＂. Moreover, their research evident indicate that the lateral line is able to ＂detect and localize vibrating sources, detect and monitor vortices, localize upstream objects, discriminate between upsteam objects （size and shape）, estimate bulk flow velocity in turbulent environment, and measure small amounts of liquid＂ （Klein, 2016 personal communication）. This review paper intends to introduce the fish mechanosensory lateral line system from several aspects that include the studies of morphological characteristics, biological origin of the system, development of the pattern formation, functional properties, behavioral neurophysiology and neural control mechanisms, finally, the biomimetic application and perspectives. We combine both of our knowledge in lateral line and recent research results in the non-canal lateral line system with broad collections of the references in the lateral line studies, especially, the new publications. We hope to provide information to readers across different disciplines, not only for theoretical consideration but also for the application in biomimetic, civic engineering, and the aquatic animal protection/biodiversity program.