Emergence of an optimal temperature in action-potential propagation through myelinated axons.

In biological organisms, an optimal temperature exists at which the system functioning is maximized or is most effective. To obtain a general and quantitative understanding of the emergence of the optimal temperature is a challenging task. We aim to gain insights into this significant problem in biological physics by addressing the problem of propagation of action potential in myelinated axons. In particular, we construct a Hodgkin-Huxley type of cortical, compartmental model to describe the nodes of Ranvier with coupling between a pair of neighboring compartments characterized by internodal conductance and investigate the effect of temperature on the propagation of the action potential. We conduct direct numerical simulations and develop a physical analysis by taking advantage of the spatially continuous approximation. We find that increasing the temperature requires a larger value of the critical internodal conductance for successful propagation. The striking finding is the spontaneous emergence of an optimal temperature in the sense that, for the propagation of a single action potential at a fixed value of the internodal conductance, the minimum average passage time for one node of Ranvier occurs at this temperature value. A remarkable phenomenon is that the value of the optimal temperature is similar to those of living biological systems observed in experiments.