Neurotransmitters in chemical synapses always excite the post-synaptic neuron. This statement is incorrect. Neurotransmitters in chemical synapses can have either excitatory or inhibitory effects on the post-synaptic neuron, depending on the type of neurotransmitter and the receptors it binds to. Excitatory neurotransmitters depolarize the post-synaptic membrane, making it more likely to generate an action potential, while inhibitory neurotransmitters hyperpolarize the membrane, making it less likely to generate an action potential.