The three types of molecular verbs and adverbs described below can thus transmit complex messages about the external and internal environment.

Amino Acids. Four chemically simple amino acids form one class of neurotransmitters. Glutamate and aspartate are excitatory neurotransmitters. GABA (gamma-amniobutyric acid) and glycine are inhibitory neurotransmitters. Glutamate and GABA are the principal verb-like neurotransmitters in the cerebral cortex (send, don't send). Glycine is a major neurotransmitter in the brainstem and spinal cord. These neurotransmitters play a key verbal role in processing specific information about the outside environment (such as color, shape, sound, and movement), and in activating the specific motor system neurons that regulate a movement.

The monoamine and peptide neurotransmitters described below play a key adverbial role in transmitting information about the changing state of our body and brain—how we currently feel about what is occurring within and without. (They modulate the actions of the amino acid neurotransmitters the way adverbs modulate the actions of verbs). Each type of monoamine and peptide is synthesized in a single brainstem or limbic system source and its circuitry spreads widely from there throughout the brain (think of a small lawn sprinkler that distributes water to a large lawn area).

Monoamines. The six types of monoamine neurotransmitters are acetylcholine, dopamine, histamine, norepinephrine (or noradrenalin), epinephrine, and serotonin. They are chemically modified amino acids that act more slowly than the amino acid neurotransmitters. The interaction of a monoamine neurotransmitter with its postsynaptic receptor helps to determine the nature of the message.