How Muscles Move Bones
Understand that muscles work in pairs to move bones: when one muscle contracts (gets shorter and pulls), the opposite muscle relaxes, and that some muscles are voluntary (we choose to use them) while others like the heart are involuntary (they work automatically)
What a learner can do afterwards
- Demonstrate or describe how biceps and triceps work as a pair to bend and straighten the arm
- Explain the difference between voluntary muscles (we control them) and involuntary muscles (they work automatically)
- Name the heart and muscles of the digestive system as examples of involuntary muscles
The lesson
Muscles move your bones, but a muscle can only pull, never push. That is why muscles work in pairs. When one muscle in the pair contracts, it gets shorter and pulls a bone. The other muscle in the pair relaxes and stretches out.
When you bend your arm, your bicep contracts and pulls, while your triceps relaxes. To straighten your arm again, your triceps contracts and pulls, while your bicep relaxes. They never both pull at the same time.
Some muscles wait for you to decide when to use them. These are voluntary muscles, like the ones in your arms and legs. Other muscles never wait. Your heart and the muscles in your stomach and intestines are involuntary. They keep working all day and night, even while you sleep, without you ever telling them to.
Muscles work in pairs, pulling to bend and straighten bones, and some muscles like your heart work automatically without you choosing.
Watch it
Where it sits
Learn first
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Nothing builds on it yet.
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.