The tension that a sarcomere can produce is related to its length. The same is true for a skeletal muscle, as it is composed of sarcomeres arranged end to end

Question

Explain how the structure of a sarcomere allows the most tension to be generated at an intermediate length, while the longest and shortest lengths will produce very little tension.

What will be an ideal response?

Answer 1

Answer: A sarcomere extends from one Z-disk to the next. Actin filaments are attached to the Z-disks, while the myosin bundle is attached at the M-line and stretches out toward the Z-disk. Neither group of proteins reaches completely across the sarcomere. When the myosin heads bind to the actin, they are able to generate tension. Thus, the more myosin is able to form cross-bridges with actin, the more tension can be generated. At the longest lengths, there is very little overlap between actin and myosin, making it difficult for any cross-bridges to form. As the sarcomere shortens, the amount of overlap and therefore cross-bridge number begins to increase. There is a small range of maximum overlap before the actin fibers from opposite Z-disks begin to overlap each other. At this point, they prevent the normal formation of cross-bridges and tension begins to decrease. Thus, the more cross-bridges that are formed, the more tension is generated. At the extremes of length, few cross-bridges exist so that little tension is produced. The intermediate length is the point where the maximum number of cross-bridges formed means the most tension is generated as well.