Final answer:
The muscular system enables voluntary movements, heartbeats, and regulation of internal organs through the contraction of skeletal, cardiac, and smooth muscles.
Step-by-step explanation:
The muscular organ system is essential for both voluntary body movements and involuntary contractions of internal organs and structures. The muscular system consists of three types of muscles: skeletal muscle, cardiac muscle, and smooth muscle. Skeletal muscles, attached to bones by tendons, facilitate voluntary movements such as standing and walking. Cardiac muscle, forming the heart's walls, beats to pump blood. Smooth muscles, found in the internal organs, regulate movements such as digestion. This system also supports the body and protects internal organs by working in concert with the skeletal system.