Neuroid Conduction and the Evolution of Conducting Tissues
Neuroid Conduction and the Evolution of Conducting Tissues
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神经样传导和传导组织的进化
DOI：
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发表时间：
1970
期刊：
影响因子：
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通讯作者：
G. Mackie
中科院分区：
文献类型：
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作者：
G. Mackie
此处定义的神经样传导是指非神经、非肌肉细胞膜中电事件的传播。描述了来自原生生物、植物和动物的例子。在甲藻夜光藻中，传播的膜去极化伴随着发光响应的传播，并且局部电变化与触手运动相关。夜光藻的导电能力归因于其独特的几何形状，其中大部分细胞质被限制在浮选液泡周围的薄外围层中，这是允许局部电流发展的条件。藻科淡水藻类显示出繁殖动作电位，其中氯离子流出是负责产生电的主要事件。根据 Grundfest (1966c)，氯化物峰值被认为是对淡水的适应。在高等植物中，捕蝇草和含羞草提供了神经样传导的例子。前者还具有触发细胞，其功能与某些动物受体类似。在含羞草中，有证据表明负责传导电事件的细胞位于维管束中，并且传播需要同时激活维管束中平行的许多细胞，就像哺乳动物平滑肌一样。在这两种情况下，细胞之间的传输被认为是通过低电阻路径进行电传输。在水母和管水母中，神经样传导发生在伞外外胚层和伞下内胚层中，这两层作为兴奋传递到外胚层平滑肌系统的传递途径相连。水母的“皱缩”行为是由该系统传递的，但神经成分可能参与了完整反应的产生。 Physonectid 管水母（例如 Nanomia）的反向运动涉及神经样途径的激活。在管水母河马中，外伞中的神经传导与发光和漂白反应耦合。所有这些形式的神经样传导提供了一种快速有效的信息传递方法。它通常与保护性和运动反应的传播有关，并且是普遍的而不是局部的。据信，更复杂和局部的反应是由神经系统组织的。在栉水母中，最近的研究表明，梳板细胞之间纤毛搏动的传播是神经样的，而纤毛活动的抑制是神经样的。纤毛沟中的某些细胞似乎代表了从非神经纤毛细胞进化而来的神经元。在棘皮动物的臀毛幼虫中，纤毛反转的协调与显然非神经起源的电信号有关。在另一种幼虫形式中，即蟾蜍爪蟾，在神经供应到达皮肤之前的阶段就已在皮肤中证明了神经样传导，使蝌蚪具有早熟的反应能力。至于传导的进化，传导组织可能在许多进化路线中独立出现。通常，传导组织是从上皮进化而来的，其中细胞通过用于代谢通讯的途径连接，这些连接的存在使组织易于传播去极化的电传输。这种组织中的有效传导单元是电耦合细胞组，而不是单个细胞本身。在动物中，神经和肌肉组织被认为是由原始肌上皮片产生的，其中通过低电阻细胞间途径进行传输。随着传导和响应系统特异性的提高，细胞之间原来的紧密耦合将被专门的突触所取代。虽然电子突触有潜力执行神经系统的许多综合功能，但化学突触总体上占了上风。
Neuroid conduction, as here defined, refers to the propagation of electrical events in the membranes of non-nervous, nonmuscular cells. Examples from protistants, plants, and animals are described. In the dinoflagellate Noctiluca, propagated membrane depolarizations accompany the spread of the luminescent response, and local electrical changes are associated with tentacle movement. The ability of Noctiluca to conduct is attributable to its peculiar geometry, in which much of the cytoplasm is confined to a thin peripheral layer surrounding the flotation vacuole, a condition that permits local current flow to develop. Fresh-water algae of the family Characeae show propagated action potentials in which chloride efflux is the major event responsible for electrogenesis. Chloride spikes are presumed to be an adaptation to fresh water, following Grundfest (1966c). Among the higher plants, Dionaea and Mimosa provide examples of neuroid conduction. The former also possess trigger cells which function in an analagous way to certain animal receptors. In Mimosa there is evidence that the cells responsible for conduction of electrical events are located in the vascular bundles and that propagation requires simultaneous activation of a number of cells lying parallel in the bundles, as in mammalian smooth muscle. In both cases transmission from cell to cell is thought to be electrical via low-resistance pathways. In hydromedusae and siphonophores neuroid conduction occurs in the exumbrellar ectoderm and subumbrellar endoderm, the two layers being linked as a transmission pathway for excitation going to ectodermal smooth muscle systems. The "crumpling" behavior of medusae is transmitted by this system, but nervous components may be involved in the generation of the full response. Reverse locomotion in physonectid siphonophores (e.g., Nanomia) involves activation of neuroid pathways. In the siphonophore Hippopodius, neuroid conduction in the exumbrella is coupled to luminescent and blanching reactions. Neuroid conduction in all these forms provides a rapid and efficient method of information transfer. It is typically associated with the spread of protective and locomotory responses and is general rather than local in effect. The more complex and local responses are believed to be organized by the nervous system. In ctenophores, recent work suggests that propagation of the ciliary beat between cells of the comb plates is neuroid, and that inhibition of ciliary activity is nervous. Certain cells in the ciliated grooves seem to represent neurons in process of evolution from non-nervous, ciliated cells. In the pluteus larva of an echinoderm, coordination of ciliary reversal is associated with electrical signals apparently of non-nervous origin. In another larval form, that of the toad Xenopus, neuroid conduction has been demonstrated in the skin at a stage before the nerve supply reaches the skin, giving the tadpole a precocious capacity for response. As for the evolution of conduction, conducting tissues probably arose independently in many lines of evolution. Frequently the conducting tissue would have evolved from an epithelium in which the cells were connected by pathways serving for metabolic communication, the existence of these junctions predisposing the tissue for electrical transmission of propagated depolarizations. The effective conducting units in such tissues would have been groups of electrically coupled cells, rather than individual cells as such. In animals, nerve and muscle tissues are considered to have arisen from primitive myoepithelial sheets in which transmission occurred through low-resistance intercellular pathways. With the need for increased specificity in the conduction and response system, the original tight coupling between the cells would be replaced by specialized synapses. While electronic synapses have the potential to perform many integrative functions of the nervous system, chemical synapses have in general prevailed.