Skeletal muscle contraction ends when:: (A) Ions move out of cytoplasm, (B) Ach is absorbed from the NMJ, (C) Closure and in­drawing of receptors, (D) Decreased calcium outside reticulum
Answer is D. “Once the Ca2+ concentration outside the reticulum has been lowered sufficiently, chemical interaction between myosin and actin ceases and the muscle relaxes.”