Final answer:
Acetylcholine (ACh) is the neurotransmitter released by motor nerve endings onto muscle, initiating muscle contraction by causing depolarization at the motor end plate.
Step-by-step explanation:
The neurotransmitter released by motor nerve endings onto muscle is acetylcholine (ACh). This chemical signal is critical for proper nervous system function and plays a key role in muscle contractions. When an action potential reaches the end of a motor neuron, it causes an influx of calcium ions, which triggers the release of acetylcholine from synaptic vesicles into the synaptic cleft. Once released, acetylcholine binds to receptors on the motor end plate of the muscle tissue, leading to depolarization and eventually muscle contraction. Acetylcholine's action at the neuromuscular junction is essential for converting electrical signals from the nervous system into mechanical movement of the muscles.