In the structure of skeletal muscle, what is a muscle fascicle?

• A. A connective tissue sheath that surrounds the entire muscle (epimysium)
• B. A bundle of muscle fibers (muscle cells) surrounded by perimysium
• C. A contractile unit within a myofibril composed of actin and myosin (sarcomere)
• D. A network of membranous tubules that stores calcium for contraction (sarcoplasmic reticulum)

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the hierarchical organization of skeletal muscle. Skeletal muscle is composed of multiple levels, starting from the whole muscle down to the smallest contractile units.
2. Step 2: Identify the connective tissue layers associated with each level. The epimysium surrounds the entire muscle, the perimysium surrounds bundles within the muscle, and the endomysium surrounds individual muscle fibers.
3. Step 3: Define a muscle fascicle. It is a bundle of muscle fibers (muscle cells) grouped together and surrounded by the perimysium connective tissue sheath.
4. Step 4: Differentiate the muscle fascicle from other structures. For example, the sarcomere is the contractile unit within myofibrils, and the sarcoplasmic reticulum is a membranous network involved in calcium storage.
5. Step 5: Conclude that the muscle fascicle is specifically the bundle of muscle fibers wrapped by perimysium, distinguishing it from the entire muscle (epimysium) and smaller units like sarcomeres.