[Paper Review] Nerves and anaesthesia: A physics perspective on medicine

Thomas Heimburg|arXiv (Cornell University)|Sep 8, 2014

Lipid Membrane Structure and Behavior30 references3 citations

TL;DR

The paper proposes a physics-based theory explaining nerve impulse propagation and anesthesia through membrane phase transitions, where nerve pulses are modeled as solitons in a melting lipid membrane. It demonstrates that anesthetics lower membrane melting temperature, inhibiting excitation, and explains the Meyer-Overton correlation via lipid solubility and phase behavior.

ABSTRACT

We present a recent theory for nerve pulse propagation and anesthesia and argue that both nerve activity and the action of anesthetics can be understood on the basis of simple physical laws. It was found experimentally that biological membranes melt from a solid state to a liquid state just below physiological temperature. Such melting processes have a profound influence on the physical properties of cell membranes. They make it possible for mechanical pulses (solitons) to travel along nerve axons. In these pulses, a region of solid phase travels in the liquid nerve membrane. These pulses display many properties associated with the action potential in nerves. Both general and local anesthetics lower melting temperatures of membranes. Thus, they make it more difficult to excite the nerve membrane. Since hydrostatic pressure increases melting temperatures, it counteracts anesthesia. This theory has the virtue of providing a simple explanation of the famous Meyer-Overton correlation, which states that the effectiveness of an anesthetic is proportional to its solubility in the lipid membranes of cells. We offer evidence that this concept if also applicable to local anesthesia. Finally, we show that the presence of transitions has an influence on channel activity that can arise even in the absence of proteins. The miracle of the appropriateness of the language of mathematics for the formula- tion of the laws of physics is a wonderful gift which we neither understand nor de- serve. We should be grateful for it and hope that it will remain valid in future re- search (Eugene Wigner, 1960).

Motivation & Objective

• To explain nerve impulse propagation using principles of condensed matter physics and membrane phase transitions.
• To resolve the long-standing Meyer-Overton correlation by linking anesthetic potency to lipid membrane solubility and melting behavior.
• To investigate how anesthetics and hydrostatic pressure modulate membrane phase states and nerve excitability.
• To explore whether ion channel activity can emerge from physical membrane properties alone, independent of protein structure.

Proposed method

• Modeling nerve membranes as two-phase systems transitioning between solid and liquid states near physiological temperature.
• Applying soliton theory to describe mechanical pulses propagating as localized phase boundaries in the membrane.
• Using thermodynamic principles to relate anesthetic solubility in lipids to changes in membrane melting temperature.
• Analyzing the effect of hydrostatic pressure on membrane phase transitions and its antagonistic role to anesthesia.
• Deriving the relationship between anesthetic potency and lipid solubility based on phase transition thermodynamics.
• Demonstrating that phase transitions can influence ion transport even in the absence of membrane proteins.

Experimental results

Research questions

• RQ1 How can nerve impulse propagation be explained through physical phase transitions in lipid membranes?
• RQ2 Why does anesthetic potency correlate with lipid solubility, as described by the Meyer-Overton rule?
• RQ3 What is the role of hydrostatic pressure in reversing anesthetic effects, and how is this linked to membrane melting?
• RQ4 Can ion channel-like activity arise from physical membrane properties without embedded proteins?
• RQ5 How do soliton-like pulses in membranes reproduce key features of action potentials?

Key findings

• Nerve impulse propagation is explained as soliton-like mechanical pulses traveling along phase boundaries in lipid membranes that undergo a solid-to-liquid transition near physiological temperature.
• General and local anesthetics lower the melting temperature of nerve membranes, reducing the likelihood of phase transition and thus inhibiting nerve excitation.
• Hydrostatic pressure increases the melting temperature of membranes, counteracting the effects of anesthetics, consistent with experimental observations.
• The theory provides a physical basis for the Meyer-Overton correlation, showing that anesthetic potency scales with lipid solubility due to its effect on membrane phase behavior.
• Phase transitions in lipid membranes can influence ion transport and membrane potential even in the absence of protein channels, suggesting a physical origin for some electrical phenomena.
• The model accounts for key biophysical features of action potentials through the dynamics of phase boundaries in a thermodynamically driven system.