What is not a characteristic of smooth muscle?

The presence of intercalated disks is a defining characteristic of cardiac muscle, not smooth muscle. Smooth muscle is distinct in its structure and function, which includes being involuntary, consisting of uninucleate cells, and having a spindle shape.

Smooth muscle fibers are indeed involuntary, meaning they are controlled by the autonomic nervous system rather than conscious thought. This allows them to perform essential functions like regulating blood vessel diameter and moving food through the digestive tract without direct control.

Additionally, smooth muscle cells are typically uninucleate, meaning each cell contains a single nucleus, which is another feature that distinguishes them from cardiac muscle cells. Lastly, the spindle shape of smooth muscle cells contributes to their function, allowing them to contract in a coordinated manner.

In summary, intercalated disks are not a feature of smooth muscle, making it the correct answer for what is not characteristic of this type of muscle tissue.