Sarcomeres are bundled within the:

1. The structure runs the length of the fibre. 2. It attaches to the sarcolemma at its end. 3. The sarcomere is bundled within the myofibril that runs the entire length of the muscle fiber. 4. So the answer is the myofibril. _Source: OpenStax 'Anatomy and Physiology 2e', Ch 10 'Muscle Tissue'_