The binding of neurotransmitter to ligand-gated ion channels in the postsynaptic membrane causes these channels to open. As soon as the neurotransmitter is removed from the synaptic cleft, the ligand-gated ion channels close. In the brief time these channels are open, ions are able to diffuse across the postsynaptic membrane down their electrochemical gradient. The result is a postsynaptic potential, a brief change in the membrane potential of the dendrites and cell body of the postsynaptic cell. 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. Sort the phrases into the appropriate bins depending on which type of postsynaptic potential they describe. If a phrase describes both types of potentials, drag it to the "both" bin.