Rocket and Raven play freeze dance. Rocket freezes mid-jump and topples onto a pillow, laughing.
"I moved too fast!" he says. "Every part had to work together."
Raven giggles. "What do you notice about all the parts in a jump?"
Nova hovers above the pillow. "Count the teammates," she says. "Bones, muscles, tendons and the brain."
Muscles and bones work as one team.
Together they make the musculoskeletal system. That is a long word!
Bones give shape. Muscles pull. Tendons connect them. The brain gives the signal.
Some of the biggest, most powerful muscles are in the calf and thigh.
The quadriceps muscles are on the front of the thigh.
Each shoulder has a deltoid muscle. It helps move the shoulder every which way.
| Team member | Its job in a jump |
|---|---|
| brain | Sends the signal to jump |
| nerves | Carry the signal to the muscles |
| leg muscles | Contract and pull |
| tendons | Pass the pull to the bones |
| bones and joints | Move at the joints to lift you up |
| Week check | True or false? |
|---|---|
| The body has more than 600 muscles. | ? |
| Muscles work in pairs because they can only pull. | ? |
| Ligaments connect muscles to bones. | ? |
| There are three kinds of muscle. | ? |
Exercise helps keep you fit and healthy.
Running, jumping, dancing and playing all use your muscles.
Muscle masters! Tomorrow is Body Lab Day. You will build a cardboard arm that really bends.