Muscle tissue is a specialized type of connective tissue responsible for generating force and movement within multicellular organisms. Physiologically, it is comprised of proteins and cells that exhibit the capacity to shorten, or contract, when stimulated by electrochemical signals. Different types of muscle tissue are categorized by their structure and control mechanism: voluntary muscle tissue, which facilitates movement against the will of the body; involuntary muscle tissue that regulates internal organs and visceral functions; and cardiac muscle tissue, which operates autonomously to maintain circulation. At the cellular level, contraction occurs through the interaction of protein filaments, most notably actin and myosin, which slide past each other within specialized units to generate tension and initiate systemic movement.