It has long been known that there is no measurable heat production associated with the nerve pulse. Rather, one finds that heat production is biphasic, and a heat release during the first phase of the action potential is followed by the reabsorption of a similar amount of heat during the second phase. We review the long history the measurement of heat production in nerves and provide a new analysis of these findings focusing on the thermodynamics of adiabatic and isentropic processes. We begin by considering adiabatic oscillations in gases, waves in layers, oscillations of springs and the reversible (or irreversible) charging and discharging of capacitors. We then apply these ideas to the heat signature of nerve pulses. Finally, we compare the temperature changes expected from the Hodgkin-Huxley model and the soliton theory for nerves. We demonstrate that heat production in nerves cannot be explained as an irreversible charging and discharging of a membrane capacitor as it is proposed in the Hodgkin-Huxley model. Instead, we conclude that it is consistent with an adiabatic pulse. However, if the nerve pulse is adiabatic, completely different physics is required to explain its features. Membrane processes must then be reversible and resemble the oscillation of springs more than resembling “a burning fuse of gunpowder” (quote A. L. Hodgkin). Theories acknowledging the adiabatic nature of the nerve pulse have recently been discussed by various authors. It forms the central core of the soliton model, which considers the nerve pulse as a localized sound pulse.

人们早就知道，没有与神经脉冲相关的可测量的热量产生。相反，人们发现热量产生是双相的，在动作电位的第一阶段释放热量之后，在第二阶段重新吸收类似数量的热量。我们回顾了测量神经产热的悠久历史，并对这些发现进行了新的分析，重点是绝热和等熵过程的热力学。我们首先考虑气体中的绝热振荡、层中的波、弹簧的振荡以及电容器的可逆（或不可逆）充电和放电。然后我们将这些想法应用于神经脉冲的热特征。最后，我们比较了霍奇金-赫胥黎模型和孤子理论对神经的预期温度变化。我们证明了神经中的热量产生不能解释为膜电容器的不可逆充电和放电，正如霍奇金 - 赫胥黎模型中提出的那样。相反，我们得出结论，它与绝热脉冲一致。但是，如果神经脉冲是绝热的，则需要完全不同的物理学来解释其特征。膜过程必须是可逆的，更像是弹簧的振荡，而不是“火药的燃烧导火索”（引用 AL Hodgkin）。最近，多位作者讨论了承认神经脉冲绝热性质的理论。它构成了孤子模型的核心，将神经脉冲视为局部声音脉冲。