I just read How does an inhibitory synapse communicate to the cell body of a neuron? and found myself asking this question ... hopefully I'm not asking the same thing
Any body possessed of a nervous system probably has hundreds of neurons. At one end of the neuron is the nervous system, at the other - the organ.
A neuron is connected to several others in the vicinity through it's dendrites. When a 'signal' (for want of better word) is put on the system bus - how does a neuron know whether it has to act ( contract/relax it's associated muscle/organ ) on the signal, or pass it on ( forward ) after amplification of the signal, if necessary?
Is there something like a chemical protocol to identify the target neuron/group-of-neurons that form the destination?