Neurotransmitters are electrochemical messengers that transmit nerve impulses across the synaptic gap during the process of synaptic transmission. Some neurotransmitters are excitatory and some are inhibitory. Excitatory neurotransmitters (e.g. noradrenaline) make the post synaptic cell more likely to fire, whereas inhibitory neurotransmitters (e.g. GABA) make them less likely to fire. For example, if an excitatory neurotransmitter like noradrenaline binds to the postsynaptic receptors it will cause an electrical charge in the cell membrane which results in an excitatory post-synaptic potential (EPSP), which makes the post-synaptic cell more likely to fire. Whereas, if an inhibitory neurotransmitter like GABA binds to the post-synaptic receptors it will result in an inhibitory post-synaptic potential (IPSP), which makes the post-synaptic cell less likely to fire.