Muscles
Primary 4 · Science and Elementary Technology
Muscles
Lesson 1 of 5
15 min
Let's begin
Gatete makes a fist and bends his arm. "Look at my muscle!" A bump on his upper arm grows bigger and harder. Put your hand on your chest: your heart is beating too, and it is also a muscle. But Gatete never has to tell it to work!
A muscle is a soft part of the body that can contract (get shorter and thicker) and relax (get longer and thinner again). You have more than 600 muscles. They make every movement you make: walking, blinking, breathing, even your heartbeat.
The fastest muscles in your body are the ones that close your eyelids. That is why we say something happened "in the blink of an eye"!
| Type | Where it is | Voluntary or involuntary? | What it does |
|---|---|---|---|
| Skeletal muscle | attached to bones by tough cords called tendons | voluntary | moves the bones of the skeleton; it gets tired when you use it a lot |
| Smooth muscle | in the walls of the stomach, intestines, blood vessels and bladder, and in the iris of the eye | involuntary | squeezes slowly, in waves, for example to push food along |
| Cardiac muscle (heart muscle) | only in the heart | involuntary | pumps blood around the body, beating all your life |
Tip
Skeletal: you Steer it. Smooth: it's in your Stomach. Cardiac: it Can't stop!
Try each one first, then tap Show answer to check.
What happens to a muscle when it contracts?
Answer: It gets shorter and thicker.
Is the heart muscle voluntary or involuntary?
Answer: Involuntary: it works on its own.
Where is smooth muscle found? Name two places.
Answer: Any two of: the walls of the stomach, intestines, blood vessels and bladder, and the iris of the eye.
What joins a skeletal muscle to a bone?
Answer: A tendon.
Keza decides to kick a ball. Which type of muscle does she use?
Answer: Skeletal (voluntary) muscle.
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
