  Nuclear spirals can provide a wealth of information about the nuclear
potential in disc galaxies. They form naturally as a gas response to
non-axisymmetry in the gravitational potential, even if the degree of this
asymmetry is very small. Linear wave theory well describes weak nuclear
spirals, but stronger asymmetries in the potential induce waves beyond the
linear regime, which appear as spiral shocks. If a central massive black hole
(MBH) is present, spiral shocks can extend all the way to its immediate
vicinity, and generate gas inflow up to 0.03 Msun/yr. This coincides with the
accretion rates needed to power local Active Galactic Nuclei.
