Question

Compared to skeletal muscles, smooth muscle cells are (A) uninucleated, rapidly contracting, and under voluntary control (B) uninucleated, slowly contracting, and under involuntary control (C) multinucleated, rapidly contracting, and under voluntary control (D) uninucleated, slowly contracting, and under voluntary control (E) multinucleated, rapidly contracting, and contain intercalated discs

Short answer

The correct answer is (B). Smooth muscle cells are uninucleated, slowly contracting, and under involuntary control.

Step-by-step solution

Identification of the characteristics of smooth muscle cells

Smooth muscle cells are uninucleated, which eliminates option (C) and (E).

Understanding the contraction rate of smooth muscle cells

Smooth muscle cells contract slower than skeletal muscles. This eliminates option (A).

Determining the degree of control over smooth muscle cells

Smooth muscle cells are mostly under involuntary control, as body functions such as digestion and blood circulation that they control do not require conscious thought. This eliminates option (D).

Key concepts

Smooth Muscle Characteristics

Smooth muscle is a unique type of muscle tissue in the body that exhibits distinct characteristics differentiating it from other muscle types like skeletal muscle. One of the main features of smooth muscle cells is that they are uninucleated, meaning each cell contains just one nucleus. This is in contrast to multinucleated skeletal muscle cells.

In terms of appearance, smooth muscle lacks the striations or stripes found in skeletal muscle and cardiac muscle. This is why it's called "smooth." These muscle cells are typically spindle-shaped, which allows them to stretch more and maintain contractile function over various lengths.

Smooth muscle contraction is generally slower compared to skeletal muscle. This slower contraction is ideal for their roles in hollow organs where gradual or sustained tension is required, such as the walls of the intestines and blood vessels. They operate over extended periods without fatigue, a necessity for functions like digestion and maintaining blood vessel pressure.

Voluntary vs Involuntary Muscle Control

Muscle control is categorized into voluntary and involuntary control, each serving different functions in the body. Voluntary muscle control refers to muscle actions we can consciously control, such as moving the arms or legs, involving skeletal muscles. In contrast, involuntary muscle control occurs unconsciously, vital for survival and the body's ongoing processes.

Smooth muscle is primarily under involuntary control. This means the brain and nervous system coordinate their activity without requiring conscious input.
Examples of involuntary actions include:

• Peristalsis in the digestive tract, which pushes food along
• Constriction and dilation of blood vessels, regulating blood flow
• The control of the diameter of air passages in the respiratory system

Meanwhile, voluntary muscles like skeletal muscles are involved in activities that demand conscious direction, such as voluntary movements, posture maintenance, and fine motor skills.

Skeletal Muscle Comparison

When comparing skeletal muscles to smooth muscles, several differences stand out, driven by their structure, functionality, and location in the body.

Skeletal muscles are typically attached to bones and are characterized by their striated appearance. These muscles are multinucleated and have a more rapid contraction rate, which supports their role in quick, forceful movements necessary for motion and activity.

Functionally, skeletal muscles are under voluntary control, allowing for intentional movement. Tasks like walking, writing, and running rely on skeletal muscles.

In contrast, smooth muscles are non-striated and uninucleated. They contract more slowly and are found in the walls of hollow organs like the stomach and blood vessels. Their involuntary control is suited to continuous, unconscious processes such as digestion and circulation, which do not require rapid changes in movement.

Thus, while skeletal muscles excel in voluntary movement and rapid response, smooth muscles specialize in sustained, methodical contractions necessary for internal bodily functions.