Andersen Søren S L, Jackson Andrew D, Heimburg Thomas
The Niels Bohr Institute, University of Copenhagen, Copenhagen Ø, Denmark.
Prog Neurobiol. 2009 Jun;88(2):104-13. doi: 10.1016/j.pneurobio.2009.03.002. Epub 2009 Mar 13.
Nerve membranes consist of an approximately equal mixture of lipids and proteins. The propagation of nerve pulses is usually described with the ionic hypothesis, also known as the Hodgkin-Huxley model. This model assumes that proteins alone enable nerves to conduct signals due to the ability of various ion channel proteins to transport selectively sodium and potassium ions. While the ionic hypothesis describes electrical aspects of the action potential, it does not provide a theoretical framework for understanding other experimentally observed phenomena associated with nerve pulse propagation. This fact has led to a revised view of the action potential based on the laws of thermodynamics and the assumption that membrane lipids play a fundamental role in the propagation of nerve pulses. In general terms, we describe how pulses propagating in nerve membranes resemble propagating sound waves. We explain how the language of thermodynamics enables us to account for a number of phenomena not addressed by the ionic hypothesis. These include a thermodynamic explanation of the effect of anesthetics, the induction of action potentials by local nerve cooling, the physical expansion of nerves during pulse propagation, reversible heat production and the absence of net heat release during the action potential. We describe how these measurable features of a propagating nerve pulse, as well as the observed voltage change that accompanies an action potential, represent different aspects of a single phenomenon that can be predicted and explained by thermodynamics. We suggest that the proteins and lipids of the nerve membrane naturally constitute a single ensemble with thermodynamic properties appropriate for the description of a broad range of phenomena associated with a propagating nerve pulse.
神经膜由脂质和蛋白质大致等量的混合物组成。神经脉冲的传播通常用离子假说（也称为霍奇金 - 赫胥黎模型）来描述。该模型假定，由于各种离子通道蛋白具有选择性运输钠离子和钾离子的能力，仅蛋白质就能使神经传导信号。虽然离子假说描述了动作电位的电学方面，但它没有为理解与神经脉冲传播相关的其他实验观察到的现象提供理论框架。这一事实导致了基于热力学定律和膜脂质在神经脉冲传播中起基本作用这一假设的对动作电位的修正观点。概括地说，我们描述了在神经膜中传播的脉冲如何类似于传播的声波。我们解释了热力学语言如何使我们能够解释离子假说未涉及的一些现象。这些现象包括对麻醉剂作用的热力学解释、局部神经冷却诱导动作电位、脉冲传播期间神经的物理膨胀、可逆产热以及动作电位期间无净热释放。我们描述了传播的神经脉冲的这些可测量特征，以及伴随动作电位观察到的电压变化，如何代表单一现象的不同方面，而这一现象可以由热力学预测和解释。我们认为神经膜的蛋白质和脂质自然地构成了一个具有适合描述与传播的神经脉冲相关的广泛现象的热力学性质的单一整体。
