In the context of sliding filament theory, the contractile unit of skeletal muscle is the:

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

Answer: (A)

Verified step by step guidance

1. Understand the sliding filament theory, which explains how muscle contraction occurs at the microscopic level within skeletal muscle fibers.
2. Recognize that the contractile unit of skeletal muscle is the smallest segment where actin and myosin filaments slide past each other to shorten the muscle.
3. Identify the sarcomere as the repeating structural unit within a myofibril, bounded by Z-discs, where the sliding of filaments takes place.
4. Differentiate the sarcomere from other structures: the sarcolemma is the muscle cell membrane, the myofibril is a bundle of sarcomeres, and the fascicle is a bundle of muscle fibers.
5. Conclude that the sarcomere is the correct answer because it is the fundamental contractile unit responsible for muscle contraction according to the sliding filament theory.