Sarcomeres are the fundamental contractile units within myofibrils of striated muscles. Both thick filaments and thick filaments could be found within the sarcomeres along with contractile proteins, actin (thin filaments) and myosin (thick filaments). Different components have made up the banding structures of sarcomeres:
One sarcomere is divided into three bands and one zone - Two I-bands, one A-band, and a H-zone. Starting from A-band, which is the dar, middle part of the sarcomere that extends the entire length of the thick filaments and also includes those parts of the thin filaments that overlap with the thick filaments. On the sides of A-band are I-bands; they are the lighter, less dense area of the sarcomere that contains the rest of…show more content… During this process, it is important to know that the length of myofilaments does not change, but instead, overlapping each other and shorten the sarcomere. When a body movement occurs, calcium is released from cytoplasmic reticulum, these molecules bind with troponin molecules, this causes the tropomyosin molecules to move, revealing myosin attachment site on the active myofilament. The single phosphate from ATP attach to the myosin head gets released as the heads move to connect to the attachment site on the actin; this process forms the cross-bridge. The remaining ADP is then expanded to what is called a “power-stroke”, when the myosin head pull the actin inward. Once the ADP is spent, ATP attach themselves to the myosin heads. Once attached, they are immediately broken down to ADP + Pi as the heads move back to resting position, and this is called a recovery stroke. If calcium is still present, this cycle will repeat again and the sarcomere will continue to shortened so the calcium ions are transported back to cytoplasmic reticulum and the muscle