Which of the following best describes single-unit smooth muscle tissue?


a. The fibers function individually.
b. It is found in organs that require precise control of contraction.
c. It contains gap junctions that couple the fibers electrically.
d. The amount of tension produced varies with the number of muscle cells recruited.

Verified step by step guidance

1. Step 1: Understand the characteristics of single-unit smooth muscle tissue. Single-unit smooth muscle, also known as visceral muscle, is a type of smooth muscle found in the walls of organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, and blood vessels. The cells are connected to each other via gap junctions that allow the cells to contract in a coordinated manner.
2. Step 2: Evaluate each of the given options in the context of these characteristics.
3. Step 3: Option a suggests that the fibers function individually. This is not accurate for single-unit smooth muscle tissue, as the cells are connected and work in a coordinated manner.
4. Step 4: Option b suggests that it is found in organs that require precise control of contraction. This is more characteristic of multi-unit smooth muscle tissue, which is found in places like the iris of the eye where fine control is needed.
5. Step 5: Option c suggests that it contains gap junctions that couple the fibers electrically. This is accurate for single-unit smooth muscle tissue, as the cells are connected via gap junctions that allow them to contract in a coordinated manner.
6. Step 6: Option d suggests that the amount of tension produced varies with the number of muscle cells recruited. This is more characteristic of skeletal muscle tissue, where the number of muscle fibers recruited can vary to produce different amounts of force.

Key Concepts

Single-Unit Smooth Muscle

Single-unit smooth muscle, also known as visceral smooth muscle, is a type of muscle tissue where the muscle fibers contract as a single unit. This is due to the presence of gap junctions that allow electrical signals to pass between adjacent cells, enabling coordinated contractions. This type of muscle is commonly found in the walls of hollow organs, such as the intestines and blood vessels.

Gap Junctions

Gap junctions are specialized intercellular connections that facilitate communication between adjacent cells. In single-unit smooth muscle, these junctions allow ions and small molecules to pass directly from one cell to another, ensuring that the muscle fibers contract in a synchronized manner. This is crucial for the proper functioning of organs that require rhythmic contractions, such as the digestive tract.

Muscle Recruitment

Muscle recruitment refers to the process by which the nervous system activates additional motor units to increase muscle force. In the context of smooth muscle, the amount of tension produced can vary based on the number of muscle cells that are activated. However, single-unit smooth muscle typically operates as a whole, meaning that the recruitment of individual fibers is less relevant compared to the coordinated contraction of the entire muscle layer.