When the acetylcholine binds to the receptor sites ... sodium ions diffuse through and leave the cell. sodium ions diffuse through and enter the cell. a ligand is formed. the sodium channels remain closed. the sodium channels open?

At the neural synapse, when acetylcholine is released into the synaptic cleft by the pre-synaptic neuron, the acetylcholine binds to the ligands receptors on the post-synaptic neuron. This results in the opening of the sodium ion channels allowing sodium to diffuse into the neuron. When a threshold is attained, an impulse is induced in the post-synatic neuron.