During the contraction of a vertebrate skeletal muscle fiber, calcium ions

Options:

Break the cross-bridges by acting as a co-factor inside the hydrolysis of the ATP.Transmit the action potential from the motor neurons to the muscle fiber.Spread the action potentials through the T tubules.Reestablish the polarization of the plasma membrane following an action potential.Binds with troponin, changing its shape so that myosin-binding sites on actin are exposed.Option-(5):Binds with troponin, changing its shape so that myosin-binding sites on actin are exposed.                                                                                                    

Explanation:

The vertebrates are comprised of a very complex system in which the  skeletal muscle fiber cells as whole performs the contraction and relaxation of the body organs, as the chemical balance inside these fibers is greatly effected by the over all motion of the body. While, the cell's cytoplasm either releases or consumes the specific amount and nature of the materials like calcium, potassium and other vital elements that make up the whole structure and composition of the system.