Human Skeleton
Primary 4 · Science and Elementary Technology
Human Skeleton
Lesson 3 of 4
15 min
Let's begin
Byiringiro tries to bend his elbow backwards. It will not go! But when he bowls a ball at break, his arm swings round his shoulder in a full circle. Why can one joint do so much more than the other?
A joint is a place where two or more bones meet. At most joints:
Immovable (fixed) joints: the bones are locked tightly together. The bones of your skull that cover the brain are joined like this, so they protect it well.
Slightly movable joints: each one moves only a little. The joints between the vertebrae in your backbone are like this. Together, all these small movements let you bend and twist your back.
| Type | How it moves | Examples |
|---|---|---|
| Hinge joint | in one direction only, back and forth, like a door on its hinges | elbow, knee, fingers |
| Ball-and-socket joint | the round end of one bone fits into a cup in another, so it moves in all directions, even in a circle | shoulder, hip |
| Pivot joint | one bone turns around another | neck: turning your head to say "no" |
| Gliding joint | flat bones slide over each other | wrist and ankle |
Test your joints: swing your arm in a circle (shoulder), bend and straighten your knee (knee), shake your head "no" (neck), and wave your hand (wrist).
Tip
Door = hinge (elbow, knee). Ball in a cup = ball-and-socket (shoulder, hip). Shaking your head "no" = pivot (neck).
Try each one first, then tap Show answer to check.
What type of joint is the elbow?
Answer: A hinge joint: it moves in one direction, like a door.
Which joints let your arm and leg move in all directions?
Answer: Ball-and-socket joints: the shoulder and the hip.
What type of joints join the bones that cover your brain?
Answer: Immovable (fixed) joints.
What holds the bones together at a joint?
Answer: Ligaments.
What is the smooth, slippery layer on the ends of bones at a joint?
Answer: Cartilage.
What you learned today
Sources and credits
The exercises (Try it yourself and the practice questions) are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
Quick check
Match each type of joint to an example.
Tap one on the left, then its partner on the right.
