Chemical neurotransmitters have two main ways of exerting an effect on postsynaptic neurons: by binding to ionotropic or to metabotropic receptors (Figure 2.2.1). Both receptor types are ligand-gated, meaning that they open in response to a chemical binding to them (as opposed to voltage-gated). Ionotropic receptors are membrane channels: ligand binding causes a change in flow of ions through the channel.