Hey there,
Your question states: What identifies the job of a synapse?
The synapse job is that it is basically a junction between (2) never cells which has a 2 inch gap between impulses and the neurotransmitter. A neurotransmitter is know as a never that is known to be released at the end of the never fiber. So . .by restating the question, the job of the synapse would be to permit a neuron's to pass signal to other neuron's.
Hope this helps.
~Jurgen