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Electrical excitation of a skeletal muscle fiber is coupled to muscle contraction through a process involving several molecular interactions. When an action potential propagates along a muscle fiber's membrane and the T-tubule system, it triggers the release of calcium ions from the sarcoplasmic reticulum. These ions bind to troponin on the actin filaments, causing a conformational change that exposes myosin-binding sites. The myosin heads then form cross-bridges with the actin filaments and undergo a power stroke, leading to muscle contraction. The exact mechanism of this coupling has been difficult to determine due to the complexity of the molecular interactions, potential differences in protein structures and functions among species, and the discovery of additional components and regulatory factors involved in the process.