there are two types of postsynaptic potentials: excitatory postsynaptic potentials (epsps) and inhibitory postsynaptic potentials (ipsps). an epsp is excitatory because it makes it more likely that the axon of the postsynaptic cell will trigger an action potential. conversely, an ipsp is inhibitory because it makes it less likely that the axon of the postsynaptic cell will trigger an action potential.