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

Smooth muscle is characterized as involuntary muscle tissue that is not under conscious control. It is primarily located in the walls of internal organs such as the intestines, blood vessels, bladder, and uterus. This type of muscle is unique because it does not have the striations (or banded appearance) that are typically seen in skeletal and cardiac muscle. The cells of smooth muscle are spindle-shaped and allow for the controlled movement of substances through the organ systems by contracting and relaxing.

This involuntary nature enables smooth muscles to function automatically, responding to signals from the autonomic nervous system or hormonal changes without the need for voluntary input. This is crucial for maintaining essential bodily functions, such as digestion and blood circulation, which require continuous and rhythmic contractions.