Kaplan Nursing Entrance Practice Exam

Which type of muscle is characterized by involuntary action?

1. Cardiac muscle

2. Striated muscle

3. Skeletal muscle

4. Smooth muscle

The correct answer is: Cardiac muscle

The type of muscle characterized by involuntary action is cardiac muscle. Cardiac muscle is found only in the heart and is responsible for pumping blood throughout the body. Its involuntary nature means that it operates without conscious control, allowing the heart to maintain its rhythmic contractions autonomously due to specialized pacemaker cells. While smooth muscle, which is also involuntary, contributes to functions such as moving food through the digestive tract and regulating blood vessel diameter, cardiac muscle is distinct due to its unique structure and specific function related to the heart. Striated muscle generally refers to both skeletal and cardiac muscle due to their appearance under a microscope but is not a classification that denotes involuntary action. Skeletal muscle, on the other hand, is under voluntary control, allowing for movements such as walking and lifting. Understanding these distinctions helps clarify the role of different muscle types in the human body.