In the context of sliding filament theory, what is the basic contractile unit of a skeletal muscle fiber?

• A. Myofibril
• B. Sarcomere
• C. Sarcolemma
• D. Fascicle

Answer: (B)

Verified step by step guidance

1. Understand that the sliding filament theory explains how muscle contraction occurs at the microscopic level within skeletal muscle fibers.
2. Recall that skeletal muscle fibers contain many myofibrils, which are long, cylindrical structures composed of repeating units.
3. Identify that the basic contractile unit within a myofibril is called the sarcomere, which is the segment between two Z discs.
4. Recognize that the sarcomere contains the actin (thin) and myosin (thick) filaments whose interaction causes contraction by sliding past each other.
5. Note that other options like myofibril, sarcolemma, and fascicle refer to larger structures or membranes, not the fundamental contractile unit.