OSMT (Ontario Society of Medical Technologists) Practice Exam

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What is the function of the A band in the sarcomere?

Region of thin filaments
Overlapping thick and thin filaments
Only thick filaments
Region of Z discs

The correct answer is: Overlapping thick and thin filaments

The A band in the sarcomere is crucial as it represents the area where thick and thin filaments overlap. This overlapping region is essential for muscle contraction. The thick filaments, primarily composed of myosin, run through the A band, while the thin filaments, made primarily of actin, extend into the A band from the I band. During muscle contraction, these filaments slide past one another, shortening the sarcomere and generating force. Without this overlap, the muscle would not be able to contract effectively. Context helps clarify the other options: a region of thin filaments specifically refers to the I band, which lies adjacent to the A band but does not contain myosin. The option mentioning only thick filaments describes the H zone, which is a part of the A band but lacks overlapping filaments. The Z disc serves as a boundary for the sarcomere and is located at the ends of the I bands, separate from the A band. Understanding this organization is vital for grasping muscle physiology.