Which statement best defines muscles?

Muscles are specifically defined as tissues that attach to bones and are responsible for contraction and extension. This means that muscles play a crucial role in facilitating movement in the body. When muscles contract, they pull on the bones to which they are attached, leading to movement of those bones, whether it be through flexion, extension, rotation, or other movements. This ability to contract and extend is what enables activities like walking, running, lifting, and many other physical actions necessary for daily life and functioning.

In contrast to this definition, the other options focus on different types of tissues or roles within the body. For example, linking bone to bone refers to tendons or ligaments, which serve to stabilize joints rather than create movement. Structural components of joints primarily involve cartilage and connective tissues that help in cushioning and connecting bones at joints. Lastly, tissues that support organ function are generally related to various types of connective tissues and muscles that help with the functioning of organs, but do not capture the active role of muscles in movement as distinctly as the correct definition does.