Final answer:
Acetylcholine (ACh) is the neurotransmitter released at the neuromuscular junction. It triggers depolarization and muscle contraction.
Step-by-step explanation:
Acetylcholine (ACh) is the neurotransmitter released at the neuromuscular junction. It is released by motor neurons and binds to receptors in the motor end plate, triggering depolarization. The release of ACh allows sodium ions to cross the membrane into the muscle cell, resulting in depolarization and the creation of an action potential. This action potential then spreads across the entire muscle cell, causing muscle contraction.