The physical basis of nerve impulse conduction the irreversible thermodynamic analysis of the active state

Abstract

This communication reports the thermodynamic analysis of the active state in nonmyelinated axons; it is the first step in the development of a theory of the physical basis of nerve impulse transport. The thermodynamic analysis enables one to make proper identification of material and thermal diffusion coefficients and conductivities associated with the impulse transport. Future additions to the details of the theory will involve consideration of molecular models of the axon active state. The complete macroscopic thermodynamic and microscopic statistical mechanical analyses will provide the links between the model representations and the measured quantities, e.g. conductivities and action potentials. This paper is divided into two parts. Part I is an introduction to the representation of the nerve axon used here and a general discussion of the results of the analysis of the active state obtained rigorously in Part II. The analysis contained in Part II involves an examination of the phenomenological transport equations for the coupled material (ionic) and thermal diffusion problems. By means of suitable transformations of the transport equations a correspondence with the theory of thermal explosions results. This correspondence therefore allows a detailed examination of the processes of impulse initiation and propagation. The thermodynamic analysis is macroscopic and necessarily phenomenological. Nevertheless, in spite of the macroscopic viewpoint it does enable one to make some predictions of a microscopic nature. In particular, these predictions concern the mechanism of synaptic conduction, the nature of impulse initiation at sensory receptors, and very importantly, the nature of allowable microscopic models of the impulse transport in the axon membrane. These points are discussed in the text of the paper.