  The paper concerns the multiscale modeling of a myelinated axon. Taking into
account the microstructure with alternating myelinated parts and nodes Ranvier,
we derive a nonlinear cable equation describing the potential propagation along
the axon. We assume that the myelin is not a perfect insulator, and assign a
low (asymptotically vanishing) conductivity in the myelin. Compared with the
case when myelin is assumed to have zero conductivity, an additional potential
arises in the limit equation. The coefficient in front of the effective
potential contains information about the geometry of the myelinated parts.
