What is a primary characteristic of striated muscle?

A primary characteristic of striated muscle is its striped appearance, which is due to the organized arrangement of actin and myosin filaments within the muscle fibers. This striation, visible under a microscope, is indicative of the muscle's structure and function. Striated muscle includes both skeletal and cardiac muscles, and the bands or striations play a crucial role in the muscle's ability to contract efficiently and generate force for movement or pumping blood.

Considering the other options, involuntary muscle refers specifically to smooth muscle and cardiac muscle, while striated muscle includes voluntary skeletal muscle, which is primarily under conscious control. The statement about being found only in the heart pertains to cardiac muscle, a specific type of striated muscle, whereas skeletal muscles are also striated but are not found in the heart. Lastly, striated muscle typically contracts in a quick and forceful manner (like skeletal muscle), rather than slowly, which is more characteristic of smooth muscle. Therefore, the striped appearance is indeed a definitive and distinguishing feature of striated muscle.