- One of a group of chemicals secreted by a nerve cell (neuron) to carry a chemical message to another nerve cell, often as a way of transmitting a nerve impulse. Examples of neurotransmitters include acetylcholine, dopamine, serotonin, and norepinephrine.
- A substance stored in the synaptic vesicles that is released when the axon terminal is excited by a nervous impulse. The substance then travels across the synaptic cleft to either excite or inhibit another neuron. This is accomplished by either decreasing the negativity of postsynaptic potentials (excitation), or increasing the negativity of postsynaptic potentials (inhibition). Common neurotransmitters include acetylcholine, dopamine, endorphins, adrenaline (epinephrine), gamma-aminobutyric acid (GABA), amino acids, such as glutamate and glycine, noradrenaline (norepinephrine), serotonin and substance P. Common neurotransmitters in the retina are glutamate (the primary excitatory neurotransmitter), GABA (inhibitory), glycine (inhibitory), dopamine (excitatory) and acetylcholine (excitatory).
