Final answer:
After the release of acetylcholine, calcium ions are released from the sarcoplasmic reticulum, bind to troponin on actin filaments exposing myosin binding sites, and myosin heads form cross-bridges with actin, leading to muscle contraction. The correct option is A) Calcium ions are pumped into the sarcoplasmic reticulum.
Step-by-step explanation:
After the release of acetylcholine (ACh), the following events occur during the contraction of skeletal muscle:
The binding of ACh to receptors on the muscle fiber sarcolemma leads to an action potential, which then spreads along the sarcolemma and down the T-tubules.The action potential triggers the release of calcium ions (Ca2+) from the sarcoplasmic reticulum (SR) into the sarcoplasm.Calcium ions bind to troponin on the actin filaments, causing a conformational change that moves tropomyosin away from the binding sites on actin.Myosin heads bind to the exposed active sites on the actin filaments, forming cross-bridges.
The power stroke occurs, facilitated by ATP hydrolysis, which results in the sliding of actin filaments and muscle contraction.
Regarding the choices provided in the question, option B) Myosin heads bind to actin filaments representing the events in skeletal muscle contraction following the release of ACh. The correct option is A) Calcium ions are pumped into the sarcoplasmic reticulum.