Where are neurontransmitters located?
There are two answers, depending on whether you use the older,
more restricted definition of neurotransmitter that focuses on the
transmitter origin vs. a more modern, lenient definition based on
the transmitter effect. In the former, a neurotransmitter is an
ion, molecule or protein produced, modified, and packaged for
secretion by any cell that can influence neurons via its release.
The area released is called the synaptic cleft (tight spaces
between transmitting cells and their target cells). Hence the
answer is that the transmitters are located in the source and
target cells and the cleft. A small fraction leaks out of the cleft
and is destroyed by neighboring cells. The better answer is that
ions such as heavy metals and even gases such as nitric oxide are
now known to have similar effects on neurons as "classic
neurotransmitters". Hence a "neurotransmitter" that can modulate
neurons can be located nearly anywhere and is a little fuzzy, based
on how much it needs to be modified first. E.g. zinc in vitamins
and CO in the air are pretty close to direct, but the active
ingredient of Viagra, which upregulates NO (a neurotransmitter)
indirectly, wouldn't be considered a neurotransmitter. I hope this
was both interesting and helpful!
