Final answer:
Acetylcholine neurotransmitter causes the opening of sodium ion channels on skeletal muscle, depolarizing the muscle membrane and triggering an action potential that leads to muscle contraction.
Step-by-step explanation:
Acetylcholine (ACh) neurotransmitter opens sodium ion channels on the skeletal muscle which depolarizes the muscle membrane resulting in an action potential in sarcolemma. When ACh is released and binds to receptors at the neuromuscular junction, it triggers these channels to open, allowing sodium ions (Na+) to flow into the muscle cell. This influx of positive ions causes depolarization, which is a reduction in the voltage difference between the inside and outside of the cell. This change in voltage then spreads along the sarcolemma, initiating an action potential which triggers a series of events leading to muscle contraction. The action potential travels along the sarcolemma and into the muscle fiber's interior through the system of transverse tubules, ultimately leading to the release of calcium ions and enabling the muscle contraction process according to the sliding filament model.