[GP] Q.11. What is excitation-contraction coupling ?

Ans. The skeletal muscle fiber is so large that action potentials spreading along it’s surface membrane but almost no current (impulse) flow deep within the fiber. Yet, to cause maximum muscle contraction, current (impulse) must penetrate deeply into the muscle fiber to the vicinity of the separate myofibrils and this is achieved by transmission of action potentials along transverse tubules (T tubules) that penetrate all the way through the muscle fiber from one side of the fiber to the other side. Then these action potentials cause release of calcium ions inside the muscle fiber and these calcium ions then cause contraction.
This overall process is called excitation-contraction coupling.