- The neurotransmitter predominantly released at the motor end plate to trigger skeletal muscle contraction is Acetylcholine (ACh).
- When an action potential reaches the axon terminal of a motor neuron, vesicles containing ACh fuse with the presynaptic membrane and release ACh into the synaptic cleft.
- ACh then binds to nicotinic acetylcholine receptors on the muscle fiber's motor end plate, causing the opening of ion channels.
- This results in an influx of sodium ions, leading to depolarization of the muscle membrane and initiation of an action potential in the muscle fiber.
- Consequently, this action potential triggers the process of muscle contraction.

- In contrast, other neurotransmitters listed, such as GABA (an inhibitory neurotransmitter in the CNS), norepinephrine (primarily involved in the autonomic nervous system), and dopamine (mainly involved in CNS functions related to reward and motor control), do not play a role at the skeletal muscle motor end plate.

Therefore, the exclusive neurotransmitter responsible for initiating skeletal muscle contraction at the neuromuscular junction is Acetylcholine (ACh).

Reference: Ganong's Review of Medical Physiology, 26th Edition, Chapter 10: Neuromuscular Transmission and Muscle Contraction