5. Place in order square Calcium binds to troponin square Muscle Action Potential ACh binds to receptors square Myosin binding site exposed square Thin filaments are pulled toward center the sarcomere square Calcium is released into the sarcoplasm

## Step 1<br />The first step in the process of muscle contraction is the release of calcium ions into the sarcoplasm. This is triggered by an action potential that travels down the T-tubules, which are invaginations of the sarcolemma (muscle cell membrane).<br /><br />## Step 2<br />The released calcium ions bind to troponin, a regulatory protein located on the actin filaments. This binding causes a conformational change in the troponin-tropomyosin complex, which exposes the myosin binding sites on the actin filaments.<br /><br />## Step 3<br />The myosin binding sites are exposed, allowing the myosin heads to attach to the actin filaments, forming cross-bridges.<br /><br />## Step 4<br />The muscle action potential is generated by the release of acetylcholine (ACh) from the presynaptic terminal of the motor neuron. ACh binds to its receptors on the sarcolemma, leading to depolarization of the muscle cell.<br /><br />## Step 5<br />The thin filaments are pulled toward the center of the sarcomere as the myosin heads pivot, pulling the actin filaments with them. This is known as the power stroke.<br /><br />## Step 6<br />The cycle of cross-bridge formation and breaking continues until the muscle action potential ceases, at which point the calcium ions are pumped back into the sarcoplasmic reticulum, and the muscle relaxes.