The other equation of the set resembles an equation derived from the Nernst-Planck equation, which describes transmembrane ion transport and hence provides a mechanism for transmembrane potential variation. A more complete calculation of the velocity of the asymptotic wave form shows a lower wave speed than the estimate of Nagumo {ital et} {ital al}. The piezoelectric properties of the phase compete with its curvature elasticity to produce the soliton lattice of the cell membrane, which consists of juxtaposed regions of opposite tilt orientations. The propagation of the solitary wave requires a switching electric field, which is the form for the action potential and which moves the polarized domains by ferroelectric switching.