  An action potential is typically described as a purely electrical change that
propagates along the membrane of excitable cells. However, recent experiments
have demonstrated that non-linear acoustic pulses that propagate along lipid
interfaces and traverse the melting transition, share many similar properties
with action potentials. Despite the striking experimental similarities, a
comprehensive theoretical study of acoustic pulses in lipid systems is still
lacking. Here we demonstrate that an idealized description of an interface near
phase transition captures many properties of acoustic pulses in lipid
monolayers, as well as action potentials in living cells. The possibility that
action potentials may better be described as acoustic pulses in soft interfaces
near phase transition is illustrated by the following similar properties:
correspondence of time and velocity scales, qualitative pulse shape, sigmoidal
response to stimulation amplitude (an `all-or-none' behavior), appearance in
multiple observables (particularly, an adiabatic change of temperature),
excitation by many types of stimulations, as well as annihilation upon
collision. An implication of this work is that crucial functional information
of the cell may be overlooked by focusing only on electrical measurements.
