Answer
Answer:
Steps #4 and # 6 of Fig. 10.10
#4. An action potential releases calcium ions to flow into the sarcoplasm and #6.The binding myosin heads to actin, release and the power stroke that pulls actin filaments toward center of the sarcomere.
Work Step by Step
In step #4 Calcium released from the sarcoplasmic reticulum by an AP flows into the sarcoplasm.
In Step 6, ATP powered power stroke takes place as myosin heads bind to actin filaments, release and push the actin filaments toward the center of the sarcomeres resulting in contraction and shortening of the sarcomere.
