What are the two kinds of involuntary muscles?

* Smooth muscle: Smooth muscle is found in the walls of internal organs, such as the stomach, intestines, bladder, and blood vessels. It is also found in the iris of the eye and in the muscles that control the size of the pupils. Smooth muscle is not under voluntary control, but it can be controlled by hormones and nerve signals.

* Cardiac muscle: Cardiac muscle is found only in the heart. It is a specialized type of muscle that contracts rhythmically to pump blood throughout the body. Cardiac muscle is not under voluntary control, but it is regulated by the electrical signals generated by the heart's pacemaker cells.