Which of the following represents the basic contractile unit of skeletal muscle fibers?
Solution
Correct Answer: Option B
The basic contractile unit of skeletal muscle fibers is the sarcomere.
- A skeletal muscle fiber is composed of many myofibrils, which are long, cylindrical structures running parallel within the muscle cell.
- Each myofibril is made up of repeating units called sarcomeres.
- The sarcomere is bounded by Z-discs and contains the organized arrangement of myofilaments—namely actin (thin filaments) and myosin (thick filaments).
- During muscle contraction, the interaction between these myofilaments within the sarcomere causes the muscle fiber to shorten, producing force.
- Therefore, while myofibrils and myofilaments are structural components of muscle fibers, the sarcomere is specifically the functional unit responsible for contraction.
Other terms in the options:
- Myofibril: A bundle of sarcomeres; a structural unit within muscle fibers but not the contractile unit itself.
- Muscle fascicle: A bundle of muscle fibers (cells); much larger structural organization.
- Myofilament: The actin and myosin filaments inside the sarcomere involved in contraction but not the entire contractile unit.
Hence, the correct answer is the sarcomere because it is the fundamental segment where contraction occurs.
Reference: Gray's Anatomy, 41st Edition, Volume 1, Chapter 5 - Muscular System / Pages 450-455
- A skeletal muscle fiber is composed of many myofibrils, which are long, cylindrical structures running parallel within the muscle cell.
- Each myofibril is made up of repeating units called sarcomeres.
- The sarcomere is bounded by Z-discs and contains the organized arrangement of myofilaments—namely actin (thin filaments) and myosin (thick filaments).
- During muscle contraction, the interaction between these myofilaments within the sarcomere causes the muscle fiber to shorten, producing force.
- Therefore, while myofibrils and myofilaments are structural components of muscle fibers, the sarcomere is specifically the functional unit responsible for contraction.
Other terms in the options:
- Myofibril: A bundle of sarcomeres; a structural unit within muscle fibers but not the contractile unit itself.
- Muscle fascicle: A bundle of muscle fibers (cells); much larger structural organization.
- Myofilament: The actin and myosin filaments inside the sarcomere involved in contraction but not the entire contractile unit.
Hence, the correct answer is the sarcomere because it is the fundamental segment where contraction occurs.
Reference: Gray's Anatomy, 41st Edition, Volume 1, Chapter 5 - Muscular System / Pages 450-455
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