Which of the following is a primary component of muscles?

Muscle fibers are the primary components of muscles, as they are the cells specifically responsible for contraction and movement. These long, cylindrical cells contain the necessary proteins, such as actin and myosin, that interact to produce muscle contractions. Muscle fibers are organized into bundles and are classified into different types, such as slow-twitch and fast-twitch fibers, which serve various functions in body movement and endurance.

The other options, while important in the overall structure and function of muscles, do not act as the primary components. Nerve cells are crucial for transmitting signals that initiate contractions but are not part of the muscle structure itself. Connective tissues provide support and structure to muscles by linking them to bones and surrounding them; however, they do not contribute directly to muscle contraction. Fat cells are involved in energy storage and insulation but are not components of muscle tissue. Hence, muscle fibers stand out as the essential unit that enables muscle function.