Q:

Are there any neurotransmitters that trigger all neurons? 

I'm reading into the basics of the nervous system, and am intrigued by neurotransmitters.  I understand that certain neurotransmitters can trigger more than one neuron type, and may be used as inhibitors or regulators (antagonists).  Conversely, are there any types of agonists that trigger excitation in all neurons, regardless of type?  If so, what functions do these play? 

A:

There is no such  promiscuous neurotransmitter.  There is always some difference between central and peripheral nervous system w.r.t neurotransmitter usage. 
Glutamate is one neurotransmitter which acts as an excitatory agonist in most neurons (but still.. not ALL neurons)

