what is a motor neuron? 6- what is a polarized membrane? 7- when the nerve impulses arrive at the synaptic knob, what ions flow into the synaptic knob? 8- what happens when this ion flows into the synaptic knob? 9- what is the neurotransmitter that is found inside the synaptic vesicle? 10- where does this neurotransmitter go after it is released from the synaptic knob? 11- what happens when this neurotransmitter binds to the protein receptor on the motor end plate? 12- what ion rushes through the protein gates into the muscles fiber (cell)? 13- when does the chemically regulated ion channel close on the motor end plate?