Skeletal muscle contraction is triggered by the neuromuscular junction, where a motor neuron releases acetylcholine to stimulate the sarcolemma. This leads to an action potential that travels along the sarcolemma and down the T-tubules, causing the release of calcium ions from the sarcoplasmic reticulum. The calcium ions bind to troponin, causing a conformational change in the troponin-tropomyosin complex that exposes binding sites on actin filaments. Myosin heads then attach to these sites, pulling the actin filaments inward to produce contraction.
