What part of a muscle fiber junctions with motor neuron?

The neuromuscular junction is the site where a motor neuron communicates with a muscle fiber to initiate muscle contraction. The motor neuron releases acetylcholine, which binds to receptors on the sarcolemma, the membrane of the muscle fiber, causing a change in the electrical potential across the membrane. This change in potential triggers an action potential that travels along the sarcolemma, leading to the release of calcium ions from the sarcoplasmic reticulum, which in turn bind to troponin and cause the muscle fiber to contract.