The muscular system functions to enable movement, maintain body temperature and posture. There are three main types of muscle: skeletal muscle which is voluntary and attached to bones, smooth muscle which is involuntary and inside organs, and cardiac muscle which makes up the heart. Skeletal muscle contracts to pull bones, working with the skeletal system, and contains bundles of fibers. Exercise causes muscle soreness by building up chemicals during activity and damaging fibers, leading to growth as the muscles heal.

1. Muscular System Life Science, Ms. Wells

7. Skeletal Muscle: Bundles of Fibers

10. Cardiac Muscle: Branched Fibers

11. Muscle Types: Fiber Shapes

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