“…Because of the substantial length of an axon it is, however, natural to assume that the concentration of a substance varies both with time and position along the axon. Deriving a dynamic model from a physical law, such as the conservation of mass, leads then necessarily to a partial differential equation (PDE); see [5,6,12,13,14,20,22]. The multi-compartment model by Hjort et al [8], which has a system of ODEs for each axon, is essentially a spatially discretization of a PDE.…”