NCIt definition : Endogenous signaling molecules that alter the behavior of neurons or effector cells.
Neurotransmitter is used here in its most general sense, including not only messengers
that act directly to regulate ion channels, but also those that act through second
messenger systems, and those that act at a distance from their site of release. Included
are neuromodulators, neuroregulators, neuromediators, and neurohumors, whether or
not acting at synapses.;
Alternative definition : NCI-GLOSS: A chemical that is made by nerve cells and used to communicate with other
cells, including other nerve cells and muscle cells.;