What organelle wraps and surrounds the myofibril and stores calcium? Cross bridge Sarcomere Sarcolemma Sarcoplasmic reticulum

The correct answer is the sarcoplasmic reticulum! This specialized organelle acts much like a storage unit for calcium ions, which are crucial for muscle contraction. When a muscle fiber receives a signal to contract, the sarcoplasmic reticulum releases calcium into the cytoplasm, initiating the interaction between actin and myosin filaments—essentially making those biceps bulge! Interestingly, the sarcoplasmic reticulum is also involved in muscle relaxation. Once the contraction signal ceases, it reabsorbs the calcium ions, allowing the muscle to relax. This dynamic play of calcium release and reabsorption happens swiftly, ensuring our muscles can engage in activities like running, jumping, or just waving hello with ease!