"Hey! It's Too Crowded in Here! Stop Shoving! Boy, I

"Hey! It's too crowded in here! Stop shoving! Boy, I can't wait 'til I'm free! I'm going to flow across that synapse and find the perfect receptor for me and you guys won't fit." "Oh yeah! You'd better hope you connect soon or else you'll be sucked back into this crowded room again!" This conversation is taking place among

A) postsynaptic potentials.
B) dendrites connected to a neuron.
C) sodium ions in an axon.
D) neurotransmitter molecules in a vesicle.