Which type of muscle tissue is involuntary and found in the walls of internal organs?

Smooth muscle is the correct answer as it is a type of muscle tissue that is involuntary and is primarily found in the walls of internal organs. This muscle type is responsible for various automatic functions such as constriction of blood vessels, movement of food through the digestive tract, and regulation of airflow in the lungs.

Smooth muscle consists of spindle-shaped cells that do not have striations, making them distinct from skeletal muscle, which is under voluntary control and striated in appearance. Unlike cardiac muscle, which is also involuntary but found specifically in the heart, smooth muscle serves a broader range of functions across various internal organs. The involuntary nature of smooth muscle means it operates without conscious control, allowing the body to regulate vital functions automatically.