Which type of muscles act on the lining of the body's passageways and hollow internal organs?

Smooth muscles are involuntary muscles that play a crucial role in the functioning of the body's passageways and hollow internal organs. Unlike skeletal muscles, which are under voluntary control and allow for movements like lifting and walking, smooth muscles operate automatically to control movements such as the contraction and relaxation of blood vessels and the digestive tract.

These muscles are characterized by their non-striated appearance, as they lack the banded pattern seen in skeletal muscles. This allows them to provide sustained contractions and operate continuously without conscious thought, which is essential for functions such as moving food through the digestive system, regulating blood flow, and controlling the diameter of airways in the respiratory system.

In the context of the body's systems, smooth muscles help maintain homeostasis by regulating processes like blood pressure and digestive rhythms, demonstrating their importance in everyday bodily functions.