On the Action Potential as a Propagating Density Pulse and the Role of Anesthetics

Abstract

The Hodgkin-Huxley model of nerve pulse propagation relies on ion currents through specific resistors called ion channels. We discuss a number of classical thermodynamic findings on nerves that are not contained in this classical theory. Particularly striking is the finding of reversible heat changes, thickness and phase changes of the membrane during the action potential. Data on various nerves rather suggest that a reversible density pulse accompanies the action potential of nerves. Here, we attempted to explain these phenomena by propagating solitons that depend on the presence of cooperative phase transitions in the nerve membrane. These transitions are, however, strongly influenced by the presence of anesthetics. Therefore, the thermodynamic theory of nerve pulses suggests a explanation for the famous Meyer-Overton rule that states that the critical anesthetic dose is linearly related to the solubility of the drug in the membranes.

Solitary electromechanical pulses in lobster neurons

“…Recently, there have been various reports, both theoretical and experimental, regarding the possibility of mechanical pulse propagation in artificial systems close to transitions and in nerves (14,16,17,21,22,(31)(32)(33). Heimburg and Jackson (14) argued that, close to the phase transitions found in biological tissue, electromechanical solitons with properties similar to those of the action potential can travel along the nerve axons.…”

“…The associated reversible change in energy is related to the latent heat of the membrane transition and thus to the reversible heat production found in nerves. Since the membrane changes its thickness, changes in membrane voltage of order 50mV are to be expected as a consequence of changes in its capacitance (17,18). Thus, the soliton is of an electromechanical or piezoelectric nature.…”

High-fidelity numerical simulation of solitons in the nerve axon

“…Furthermore, heat signatures from experimental data [44] indicate that the nerve pulse is an adiabatic and reversible phenomenon such as the propagation of a mechanical wave. This later observation is in conflict with the HH model that is based on irreversible dissipative processes (currents through resistors) and should lead to dissipation of heat [18]. This, however, is not observed in nerves [18,4].…”

“…This later observation is in conflict with the HH model that is based on irreversible dissipative processes (currents through resistors) and should lead to dissipation of heat [18]. This, however, is not observed in nerves [18,4].…”

“…In a series of recent publications by Heimburg et al [17,18,26,40,25] an alternative thermodynamic model is proposed in which nerve pulses are described as a reversible electro-mechanical density pulse (soliton) in the axon membrane. This model will be referred to as the nerve soliton (NS) model in the present study.…”