How do muscles extend and contrast? Answer in a few words.

Muscles extend by relaxing (lengthening) and contract by shortening through the action of muscle fibers. This process is driven by the sliding filament theory, where actin and myosin filaments interact.

Involuntary muscle tissues include cardiac muscle and smooth muscle. Cardiac muscle is found in the heart, while smooth muscle is located in various organs and blood vessels.

Striated muscle includes skeletal muscle and cardiac muscle. These muscle tissues are striated due to the organized arrangement of actin and myosin filaments, which create a pattern of light and dark bands (striations) that are visible under a microscope.

Without a skeletal system, the circulatory system would be compromised due to lack of structural support, impaired blood flow, and potential organ dysfunction. Muscles would lack attachment points for movement, affecting circulation.