A Sarcomere is Best Described as A

Question

A sarcomere is best described as a
A) moveable structural unit within a myofibril bounded by H zones.
B) fixed structural unit within a myofibril bounded by Z lines.
C) fixed structural unit within a myofibril bounded by A bands.
D) moveable structural unit within a myofibril bounded by Z lines.
E) collection of myofibrils.

Accepted Answer

A sarcomere is a moveable structural unit within a myofibril bounded by Z lines. This is where the thin (actin) and thick (myosin) filaments overlap to create muscle contraction. The H zone is the center part of the A band that only contains myosin, and the A band is the length of the myosin filament within a sarcomere. A sarcomere is not a fixed unit, as it shortens and lengthens during muscle contraction and relaxation. It is also not a collection of myofibrils, as a myofibril is composed of multiple sarcomeres.