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

The correct answer is visceral muscle, also known as smooth muscle. This type of muscle tissue is involuntary, meaning it is not under conscious control, and it is primarily responsible for the involuntary movements within internal organs such as the gastrointestinal tract, blood vessels, and respiratory system. Visceral muscle contracts to facilitate essential functions like digestion and circulation without the need for voluntary effort.

In contrast, cardiac muscle, while also involuntary and found in the heart, is specialized for pumping blood and has a distinct structure that includes intercalated discs. Skeletal muscle, on the other hand, is voluntary and enables movement of the skeleton, allowing for activities like walking and lifting. Striated muscle is a term that refers to both skeletal and cardiac muscle due to their striated appearance under a microscope, but it does not accurately describe visceral muscle, which lacks striations and functions differently in the body. Therefore, the definition and function of visceral muscle encapsulate the correct option.