Which of the following statements about the sarcoplasmic reticulum in muscle fibers is correct?

• A. The sarcoplasmic reticulum is more extensive in skeletal muscle fibers than in smooth muscle fibers.
• B. The sarcoplasmic reticulum is equally extensive in both skeletal and smooth muscle fibers.
• C. Neither skeletal nor smooth muscle fibers contain a sarcoplasmic reticulum.
• D. The sarcoplasmic reticulum is more extensive in smooth muscle fibers than in skeletal muscle fibers.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the role of the sarcoplasmic reticulum (SR) in muscle fibers. The SR is an organelle responsible for storing and releasing calcium ions, which are essential for muscle contraction.
2. Step 2: Compare the structure and function of skeletal muscle fibers and smooth muscle fibers. Skeletal muscle fibers are highly organized and require rapid calcium release for quick contractions, while smooth muscle fibers contract more slowly and do not require as extensive a calcium storage system.
3. Step 3: Analyze the differences in the sarcoplasmic reticulum between skeletal and smooth muscle fibers. Skeletal muscle fibers have a more extensive SR to support their rapid and forceful contractions, whereas smooth muscle fibers have a less developed SR due to their slower contraction mechanism.
4. Step 4: Eliminate incorrect options based on the structural and functional differences. For example, the statement 'Neither skeletal nor smooth muscle fibers contain a sarcoplasmic reticulum' is incorrect because both types of muscle fibers do contain an SR, though its extent varies.
5. Step 5: Select the correct answer by identifying the statement that aligns with the anatomical and physiological characteristics of the sarcoplasmic reticulum in skeletal and smooth muscle fibers. The correct answer is: 'The sarcoplasmic reticulum is more extensive in skeletal muscle fibers than in smooth muscle fibers.'