  We report a cylindrical-peristaltic shape transformation in axons exposed to
a controlled osmotic perturbation. The peristaltic shape relaxes and the axon
recovers its original geometry within minutes. We show that the shape
instability depends critically on swelling rate and that volume and membrane
area regulation are responsible for the shape relaxation. We propose that
volume regulation occurs via leakage of ions driven by elastic pressure, and
analyse the peristaltic shape dynamics taking into account the internal
structure of the axon. The results obtained provide a framework for
understanding peristaltic shape dynamics in nerve fibers occurring in vivo.
