Question

In an experiment, the circulating blood volume of an animal is increased by IV saline infusion. The increase in preload raises LV myocardial inotropy and SV. Further evaluation reveals an increase in sarcomere length. What region will be lengthened?

a) I band
b) H zone
c) A band
d) Z line

Answer 1

During muscle contraction, the I band and the H zone in a sarcomere shorten while the A band remains the same length. The Z line does not lengthen or shorten.

Step-by-step explanation:

When a muscle contracts, the sarcomeres within the muscle shorten. In a sarcomere, the I band contains only thin filaments and it shortens during contraction. The H zone is the central region of the A band and it also shortens. The A band, which contains both thin and thick filaments, remains the same length but the A bands of different sarcomeres move closer together. The Z line, which marks the boundary of the sarcomere, does not lengthen or shorten.