  We investigate the instabilities and bifurcations of traveling pulses in a
model excitable medium; in particular we discuss three different scenarios for
the loss of stability resp. the disappearance of stable pulses. In numerical
simulations beyond the instabilities we observe replication of pulses
(backfiring) resulting in complex periodic or spatiotemporally chaotic dynamics
as well as modulated traveling pulses. We approximate the linear stability of
traveling pulses through computations in a finite albeit large domain with
periodic boundary conditions. The critical eigenmodes at the onset of the
instabilities are related to the resulting spatiotemporal dynamics and act upon
the back of the pulses. The first scenario has been analyzed earlier for high
excitability resp. low excitation threshold: it involves the collision of a
stable pulse branch with an unstable pulse branch in a so called T-point.
