Evolution of excitability in lower metazoans

R. Meech, G. Mackie
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引用次数: 14

Abstract

All forms of life exhibit excitability; it is one of the characteristics by which living creatures can be recognized. In this chapter, we examine the different manifestations of excitability exhibited by the Metazoa and show how elements present in the Bacteria come together in the Protozoa, Porifera, Cnidaria, and Ctenophora (see Fig. 1) to form the patterns of excitability known as “behavior.” We consider the role of excitation in fertilized eggs and conducting epithelia, as well as the origins of signaling in nerves and muscles. We describe different forms of all-or-nothing signaling, as well as ways of generating graded responsiveness. This study attempts to provide a practical approach to understanding the limitations of excitable systems. We believe that defining these limits is more useful than glorifying their seemingly endless sophistication. THE NATURE OF EXCITABILITY Excitability Defined Excitability is easy to recognize; less easy to define. We recognize excitability when we see it, by the way an organism responds to an external stimulus. For there to be a response, stimulus and organism must interact and the organism must “receive” the stimulus. Inevitably, the stimulus site, or receptor, and the response site, or effector, will be at different locations even in single cells. Thus, excitability depends on the transmission of signals from receptor to effector. The signals may be chemical and spread by passive diffusion, electrical and spread by the transfer of ionic charge, or mechanical and spread by a physical disturbance. We focus in this section on the links between chemical...
低等后生动物兴奋性的进化
所有形式的生命都表现出兴奋性;这是识别生物的特征之一。在本章中,我们研究了后生动物表现出的兴奋性的不同表现,并展示了细菌中存在的元素如何在原生动物、多孔动物、刺胞动物和栉虫中聚集在一起(见图1),形成被称为“行为”的兴奋性模式。我们考虑兴奋在受精卵和传导上皮中的作用,以及信号在神经和肌肉中的起源。我们描述了不同形式的全有或全无信号,以及产生分级响应的方法。本研究试图提供一种实用的方法来理解可激系统的局限性。我们认为,界定这些限制比美化它们看似无穷无尽的复杂性更有用。兴奋性的本质兴奋性的定义很容易识别;不太容易定义。当我们看到兴奋性时,我们就会认出它,就像生物体对外部刺激的反应一样。为了产生反应,刺激和生物体必须相互作用,生物体必须“接受”刺激。不可避免的是,即使在单个细胞中,刺激点或受体和反应点或效应点也会位于不同的位置。因此,兴奋性取决于信号从受体到效应器的传递。信号可能是化学的,通过被动扩散传播;可能是电的,通过离子电荷的转移传播;也可能是机械的,通过物理扰动传播。在本节中,我们将重点讨论化学…
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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