What neurotransmitter is released at the neuromuscular junction when an action potential arrives at the motor neuron terminal?

The neurotransmitter released at the neuromuscular junction when an action potential arrives at the motor neuron is  terminalacetylcholine (ACh).  It is a small molecule neurotransmitter, which diffuses across the synaptic cleft and binds to nicotinic acetylcholine receptors (nAChRs) on the cell membrane of the muscle fiber,  the binding of ACh to the receptor can depolarize the muscle fiber, causing muscle contraction.