Does the impulse cross neuromuscular junction when a muscle contracts?

The impulse does not cross the neuromuscular junction when a muscle contracts. When an impulse reaches the end of a motor neuron, it triggers the release of a neurotransmitter substance called acetylcholine (ACh). Acetylcholine crosses the neuromuscular junction and binds to receptors on the muscle cell membrane, causing it to depolarize. This depolarization triggers an action potential in the muscle cell, which leads to muscle contraction. So the impulse does not physically cross the gap, but rather triggers a chemical signal that does.