Without joints your body could not bend- it would be stiff like a board. In the wrists and angles are gliding joints that allow bones to glide back and forth over each other. Pivot joints like the ulna and radius bones in your lower arm allow one bone to rotate in a ring of the second bone. Between the bones is a fluid that keeps the bones from rubbing against each other. At the end of the bones is cartilage to make movement smooth.
Smooth muscles are involuntary muscles.
Flat bones make up your skull, ribs, and shoulder blades. Short bones are found in your hands and feet. The contractions result when the units in each muscle cell slide together. Chemical waste products from the contraction must be carried away by the blood stream. Without joints your body could not bend- it would be stiff like a board.