Summary: Neurotransmitters are paradoxical molecules; they are both highly diverse and extremely alike. These molecules all have the same basic function – to transmit signals across a synapse. Some of these signals are excitatory, some inhibitory, and others facilitatory, but they all convey a message to the postsynaptic cell. Of those listed, acetylcholine is the most common as well as the most well studied. This is NOT a comprehensive list of neurotransmitters, far more exist, some known and some unknown to science.