The correct answer is: D) Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell.
The motor neuron cell is connected to muscle cell via synaptic cleft, where neurotransmitter is released. The muscle side of this synapse is called motor end plate. Released neurotransmitter is acetylcholine and it binds to its receptor (ACh receptor) on the motor end plate. As it binds, ion channels open, and Na+ gets into the muscle cell. This event reduces the voltage difference between the inside and outside of the cell and causes depolarization which creates a wave through the entire muscle cell (its membrane-sarcolema). As a consequence, Ca2+ is released from the sarcoplasmic reticulum which will cause the contraction of the muscle cell.
