Which of the following best explains why smooth muscle can maintain a forceful contraction longer than skeletal muscle?

• A. Smooth muscle contracts only in response to voluntary nervous stimulation.
• B. Smooth muscle fibers are larger and contain more mitochondria than skeletal muscle fibers.
• C. Smooth muscle uses less ATP and has slower cross-bridge cycling than skeletal muscle.
• D. Smooth muscle contains sarcomeres arranged in a regular pattern like skeletal muscle.

Answer: (C)

Verified step by step guidance

1. Understand the key differences between smooth muscle and skeletal muscle. Smooth muscle is found in the walls of hollow organs (e.g., blood vessels, intestines) and is involuntary, while skeletal muscle is attached to bones and is under voluntary control.
2. Review the energy usage in muscle contraction. Smooth muscle uses less ATP during contraction because it has slower cross-bridge cycling compared to skeletal muscle. This slower cycling reduces the energy demand.
3. Examine the structural differences. Smooth muscle does not contain sarcomeres arranged in a regular pattern like skeletal muscle. Instead, its actin and myosin filaments are arranged in a more irregular, lattice-like pattern, which contributes to its ability to sustain contractions for longer periods.
4. Consider the physiological function. Smooth muscle is designed to maintain prolonged contractions, such as in blood vessel tone or peristalsis, without fatigue. Skeletal muscle, on the other hand, is designed for quick, forceful contractions but fatigues more rapidly.
5. Eliminate incorrect options. Smooth muscle does not contract only in response to voluntary nervous stimulation, nor does it have larger fibers or more mitochondria than skeletal muscle. The correct explanation is that smooth muscle uses less ATP and has slower cross-bridge cycling, allowing it to maintain forceful contractions longer.