A skeletal muscle sarcomere is shown above. The ability of a resting sarcomere to contract is dependent on the existence of an overlap between actin and myosin filaments and the presence of a gap between the ends of the actin filaments and the M-line. Given this, which of the following diagrams best represents a resting sarcomere with the potential to generate the greatest amount of contractile force?

Question

A skeletal muscle sarcomere is shown above.  The ability of a resting sarcomere to contract is dependent on the existence of an overlap between actin and myosin filaments and the presence of a gap between the ends of the actin filaments and the M-line.  Given this, which of the following diagrams best represents a resting sarcomere with the potential to generate the greatest amount of contractile force?

Quizplus · Accepted Answer

11ecba2d_1035_8456_a3bf_6be06df42752_MD0008_00 Skeletal muscle, comprised of multinucleated muscle fiber cells, facilitates voluntary movement. Each muscle fiber contains thousands of individual functional units called sarcomeres. Sarcomeres consist of both thin filaments (actin) and thick filaments (myosin), and muscle contraction depends on the interaction between these filaments. During skeletal muscle contraction, myosin heads bind the actin filaments and slide them toward the center of the sarcomere (ie, the M-line), shortening the sarcomere's overall length. When muscle relaxes, myosin heads release the actin filaments and the sarcomere returns to its original resting length. The question states that the ability of a resting sarcomere to contract is dependent on the existence of overlap between actin and myosin filaments and the presence of a gap between the ends of the actin filaments and the M-line. At the ideal sarcomere resting length, actin filaments must overlap with myosin filaments to allow maximum binding of myosin heads to actin on contraction. In addition, the distance between the ends of the actin filaments and the M-line should be maximized to provide the greatest distance for actin filaments to slide during contraction. Sarcomeres exhibiting these characteristics will be able to generate the greatest amount of contractile force. (Choice C) Resting sarcomeres that are overly stretched will exhibit minimal overlap of thin actin filaments with thick myosin filaments. Accordingly, myosin heads will be less able to bind and slide the actin filaments during contraction, leading to a reduction in contractile force. (Choices B and D) When resting sarcomeres are overly compressed, the ends of the actin filaments are too close together. The distance available for actin filaments to slide toward the M-line during contraction is reduced, leading to a decrease in the amount of contractile force that can be generated by the sarcomere. Educational objective: Skeletal muscle fibers consist of thousands of individual functional units called sarcomeres, and each sarcomere is comprised of both thin actin and thick myosin filaments. On muscle contraction, myosin heads bind the actin filaments and slide them toward the center of the sarcomere.

A Skeletal Muscle Sarcomere Is Shown Above