What is the appearance of smooth muscle?

Smooth muscle is characterized by its non-striated appearance and is classified as involuntary muscle. This type of muscle is called "smooth" because it does not have the striations (or bands) that are found in skeletal and cardiac muscle. The absence of striations is due to the arrangement of actin and myosin filaments, which are not organized into sarcomeres, the structural units found in striated muscle.

Involuntary means that smooth muscle operates autonomously, without conscious control from the nervous system. This is critical for its function in various internal processes, such as regulating blood vessel diameter, moving food through the digestive tract, and controlling the contraction of organs like the bladder.

The other options mention either striated muscle or voluntary control, which are not attributes of smooth muscle. Striated muscles, like skeletal and cardiac muscles, have a banded appearance due to their organized tissue structure and are mostly under voluntary or semi-voluntary control in the case of cardiac muscle.