We analyze a model of mutually propelled filaments suspended in a two-dimensional solvent. The
system undergoes a mean-field isotropic-nematic transition for large enough filament concentrations, and
the nematic order parameter is allowed to vary in space and time. We show that the interplay between
nonuniform nematic order, activity, and flow results in spatially modulated relaxation oscillations, similar
to those seen in excitable media. In this regime the dynamics consists of nearly stationary periods
separated by ‘‘bursts’’ of activity in which the system is elastically distorted and solvent is pumped
throughout. At even higher activity, the dynamics becomes chaotic