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Ok-

But even that does not explain how a neuron determines which neurotransmitter to release (which in turn, determines the message being spread across the synapse). I think Kate is asking how, after depolarization, is the signal that (let's just say) invokes movement in my finger out of pain differentiated from a signal that invokes movement in that same finger as a conscious gesture? If all action potentials are the same and if the motorneuron in my finger for finger movement are the same, then where is this signal encoded? And, I think she was hinting at neurotransmitters: that which transmitter is released dictates the output, but what dictates that neurotransmitter's release? And though I think what you've said is important, the question arises: then how is it determined which neurons it passes through? I am not saying that I have the answer, or that we are expected to, and though I think what you've said is part of it, it isn't all of it. I considered that maybe certain neurons were coded for certain signals, and that level of organization would not surprise me, but I thought the uniquness of the brain lay in the structural changes that can be made, rather than the variety of neurons. I guess my biggest question is, after an input (say, I touch a hot stove), and action potential is propagated, and how does it know what the input was right from the get-go? How is what happens next determined? Let's start with the beginning.