Question

If a myofibril were pulled so that the sarcomeres increased in length by approximately 50 percent, what effect would you expect this to have on the contractile ability of the myofibril? Why? What effects would this have on the H, A, and I bands?

Answer 1

Increasing the length of sarcomeres in a myofibril by 50 per cent would decrease its contractile ability due to insufficient overlap of actin and myosin filaments, based on the length-tension relationship. The H and I bands would increase in size, while the A band would remain unchanged.

Step-by-step explanation:

If a myofibril were pulled so that the sarcomeres increased in length by approximately 50 per cent, the contractile ability of the myofibril would be significantly reduced. This is because the length-tension relationship dictates that there is an optimal overlap between actin and myosin filaments for maximal tension generation. According to the sliding filament theory, when sarcomeres are stretched beyond 120% of their resting length, the overlap between the actin and myosin is insufficient, resulting in less tension produced during muscle contraction.

Regarding the muscle bands, the H band would increase in size, as it consists only of myosin filaments and is widened when the sarcomere is lengthened. The A band remains constant since it reflects the length of the myosin filaments which does not change. Lastly, the I band, which contains only actin filaments, would also increase as it includes parts of the sarcomere that lengthen due to the pulling apart of the Z lines.