  Objective: We confirm that alteration of a neuron structure can induce
abnormalities in signal propagation for nervous systems, as observed in brain
damage. Here, we investigate the effects of geometrical changes and damage of a
neuron structure in 2 scaled nerve bundle models, made of myelinated nerve
fibers or unmyelinated nerve fibers.
  Methods: We propose a 3D finite element model of nerve bundles, combining a
real-time full electromechanical coupling, a modulated threshold for spiking
activation, and independent alteration of the electrical properties for each
fiber. We then simulate mechanical compression and tension to induce damage at
the membrane of a nerve bundle made of 4 fibers. We examine the resulting
changes in strain and neural activity by considering in turn the cases of
intact and traumatized nerve membranes.
  Results: Our results show lower strain and lower electrophysiological
impairments in unmyelinated fibers than in myelinated fibers, higher
deformation levels in larger bundles, and higher electrophysiological
impairments in smaller bundles.
  Conclusion: We conclude that the insulation sheath of myelin constricts the
membrane deformation and scatters plastic strains within the bundle, that
larger bundles deform more than small bundles, and that small fibers tolerate a
higher level of elongation before mechanical failure.
