How nerve impulse sent to muscle?

A signal is generated in the motor cortex of the brain, and travels down the spinal cord to the affected motor neurons. As the action potential travels down the axon of the final motor neuron, it causes calcium influx and exocytosis of acetylcholine-containing vesicles, releasing acetylcholine into the neuromuscular junction. From there, acetylcholine binds with receptors on the muscle fiber end plates, where it depolarizes the muscle fiber, causing contraction of the muscle.