Movement needs four parts working together: bones give the lever, joints give the pivot, muscles give the pull, and connective tissue holds everything in place. This lesson gives each part one job and then shows them working as a chain.
It belongs to support and movement. The next lesson, explaining antagonistic muscle action, builds directly on it.
What is the job of each part?
Give each part a single verb and you will rarely mix them up.
| Part | Job | Connects |
|---|---|---|
| Bone | Supports the body and acts as a lever | Joint to joint |
| Joint | Allows movement at a pivot | Two or more bones |
| Muscle | Contracts to pull | Two bones, via tendons |
| Tendon | Transmits the muscle’s pull | Muscle to bone |
| Ligament | Keeps bones in place at a joint | Bone to bone |
| Cartilage | Reduces friction and absorbs shock | Covers bone ends |
How does the chain work?
The brain sends a signal, the muscle shortens, the tendon pulls the bone, and the bone turns around the joint. Each link passes the force on to the next.
If one link is missing, movement fails. A torn ligament lets the joint slip, while a cut tendon means the muscle contracts but the bone does not move.
Worked example: lifting a book with the forearm
Sara holds a book in her hand and bends her elbow to lift it. Trace the force.
- The biceps receives a signal and contracts, so it shortens.
- The tendon at the lower end of the biceps pulls on the radius.
- The radius acts as a lever and rotates around the elbow joint, a hinge joint.
- Cartilage and synovial fluid at the elbow keep the bone ends sliding smoothly.
- Ligaments at the elbow stop the forearm from twisting out of line.
Write this as a sentence: “The biceps contracts and its tendon pulls the radius, which turns around the elbow joint to lift the forearm.”
The mix-up that loses marks
A common answer says “the ligament pulls the bone”. It sounds close, but it names the wrong structure.
| Statement | Correct? | Fix |
|---|---|---|
| Ligament joins muscle to bone | No | Tendon joins muscle to bone |
| Tendon stretches a lot to help movement | No | Tendons are strong and transmit force without much stretch |
| Muscle pushes the bone up | No | Muscle only pulls |
| Ligament holds bones together at a joint | Yes | Correct |
Check yourself
A student says: “The ligament contracts and pulls on the bone to bend the knee.” Write the corrected sentence and name the joint type.
Answer
Ligaments do not contract. The corrected sentence is: “The muscle contracts and its tendon pulls on the bone, so the lower leg bends at the knee.”
The knee is a hinge joint, which allows movement in one plane, like a door.
What to study next
Move on to explaining antagonistic muscle action to see why muscles work in pairs. Log your slips in the mistake log and paper-error review, then try the support and movement practice set.
A teacher can quiz you on structures and functions while you answer aloud. See online one-to-one Biology tuition.