Which of the following is NOT characteristic of involuntary muscle?

Involuntary muscle is defined by the fact that it operates without conscious thought or control. This type of muscle is responsible for automatic functions within the body, such as regulating the heartbeat or moving food through the digestive tract.

The characteristic of involuntary muscle that stands out is its ability to contract automatically without conscious direction. This means that these muscles are not under voluntary control, which aligns with their role in bodily functions that need to occur continuously and reliably without the need for deliberate action.

Involuntary muscle is primarily found in the walls of hollow organs like the intestines and blood vessels, further emphasizing its automatic function. Additionally, it creates movement and enables essential bodily operations without the need for conscious thought or effort.

The choice that states it is "under the control of the will" does not align with the definition of involuntary muscle, as such muscles are not controlled consciously but rather respond to physiological signals. This makes the chosen answer accurate.