1) Neurotransmitters are chemicals that transmit signals between neurons in the brain and body, allowing communication throughout the nervous system. They can affect mood, sleep, concentration and other functions. 2) Neurotransmitters are synthesized in neurons and stored in vesicles, then released into the synaptic cleft and bind to receptors on the postsynaptic neuron. This may cause excitation or inhibition of the postsynaptic neuron. 3) Common neurotransmitters include glutamate, GABA, dopamine, serotonin, acetylcholine, and norepinephrine. They have different functions and are broken down or reabsorbed after signaling to terminate their effects.