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neurotransmitter
neurotransmitter A neurotransmitter is a naturally produced signaling chemical that changes the activity of neurons or other target cells.
A neurotransmitter is a naturally produced signaling chemical that changes the activity of neurons or other target cells. In the broad sense, it includes substances that act directly on ion channels, work through second-messenger pathways, or influence cells at some distance from where they are released, including effects outside synapses.