This question is coming out of a couple points of confusion after I learned about about NMDA receptors' role in LTP.
I got the impression that after AMPA receptors were activated enough, which depolarizes the cell, that nearby NMDA receptors will allow Na and Ca to come into the cell.
Is it the local membrane potential, around those receptors that matter for a given voltage-gated NMDAR to open up? Or is there no such thing as 'local membrane potential', and the whole cell body is about the same amount of negative or positive voltage?
If there's no such thing as 'local membrane potential', does it matter if the AMPA receptors are activated or if other receptors are activated? Does a single neuron usually respond to more than one type of excitatory neurotransmitter? If so, couldn't the activation of any receptor that results in cell depolarization eventually cause NMDAR to open up?