So along the membrane we have many of these Ligand gated on channels we call Acetylcholine receptors. And they're essentially closed. Now, because they're closed, the sodium ions, which are found at a higher concentration on the outside of the cell, cannot move into the cell. But what happens is when an action potential basically reaches this section of the neuron, it stimulates these vesicles to be released to this environment. And once these vesicles are released via exocytosis, they release these neurotransmitters we call Acetylcholine. And acetylcholine is the ligand that binds onto these ligand gated ion channels, which open up and then allow the spontaneous movement of these sodium ions from the outside into the inside of that cell.