A) Rigor mortis occurs as a result of a rise in intracellular calcium concentrations. B) In skeletal muscle a single action potential lasts about 5-10 msec. C) In skeletal muscle the relaxation time lasts slightly longer than the contractile time. D) In skeletal muscle the contractile response ceases when the lateral sacs take up Ca2+. E) A spring can move much faster than a muscle can contract.