Which of the following is true of smooth muscle?
A) ?Smooth muscle can shorten more relative to its length compared with striated (skeletal) ?muscle.
B) ?It can’t maintain a steady state of contraction.
C) ?Smooth muscle can’t maintain an even amount of tension.
D) ?It’s under voluntary control.
The Correct Answer and Explanation is:
Correct Answer: A) Smooth muscle can shorten more relative to its length compared with striated (skeletal) muscle.
Explanation:
Smooth muscle is a type of involuntary, non-striated muscle found in the walls of hollow organs such as the intestines, blood vessels, bladder, and uterus. It plays a vital role in various physiological functions such as regulating blood pressure, moving food through the digestive system, and controlling airflow in the lungs.
Option A is correct because smooth muscle cells are designed for significant shortening. Unlike skeletal (striated) muscle fibers, which have a fixed sarcomere arrangement, smooth muscle cells have actin and myosin filaments arranged in a less organized fashion. This structural arrangement allows them to contract over a greater percentage of their resting length. Smooth muscle can contract to as little as 20–30% of its original length, making it highly adaptable in organs that need to change shape or volume significantly (e.g., the bladder or uterus).
Option B is incorrect because smooth muscle can maintain a steady state of contraction, known as the latch state. This allows it to hold contractions for long periods with minimal energy expenditure, which is important in organs such as blood vessels, where maintaining tone is essential.
Option C is incorrect because smooth muscle can maintain a consistent amount of tension over time. This is crucial in maintaining functions such as vascular resistance and gastrointestinal tone.
Option D is incorrect because smooth muscle is not under voluntary control. It is regulated involuntarily by the autonomic nervous system, hormones, and local chemical signals.
In summary, smooth muscle’s ability to shorten extensively relative to its length, while maintaining tone and contractions over time without fatigue, makes option A the correct and most accurate statement.
