Inside Bones

The skeleton is your body’s internal supporting structure. It holds everything together. In addition to providing support, bones act as shock absorbers when you jump, fall, and run. Bones have big responsibilities and so they must be really strong. They also need to be arranged properly for the best support and shock absorption.

In this experiment, we will look at the internal arrangement of the bones holding together your body.

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Here’s what you need

• 1 toilet paper tube
• 50-100 straws
• 1 roll of tape
• 1 book

Download Student Worksheet & Exercises

Here’s what you do

1. First you will explore different bone structures. Start by taking 20 skinny straws and arrange them randomly in your hand so that they are pointing in different directions.
2. Lay your arm and hand on a table so that it is braced. Next, have a friend place a heavy book on this column of straws. What happens then it’s exposed to the weight?
3. Now take 20 more straws and arrange in a circle so that they are all held vertically in your hand.
4. Repeat step 2 with these more organized straws. Do you notice a difference? The uniformly arranged straws should be stronger than those that were randomly arranged.
5. The tubes inside your bones are more like the uniform model of straws. They also have a kind of glue that hold them in place inside the bones. Let’s incorporate this idea into your model by lining the inside of the toilet paper tube with tape.
6. Next, add some straws inside the tube as well. Add a single layer of straws, then another layer on top of it. Finally, fill the middle of the tube with straws, making sure they are tightly packed.
7. Test your model’s strength by placing a book on top of the tube. What happens when the model is exposed to the book’s weight?
8. For an extra study opportunity, visit the butcher in your local grocery store and ask for the end of a beef bone. (This is sometimes packaged as a soup bone). Look at the end of the bone. What do you see? It should look like a hard outer shell of bone protecting a softer, spongy portion. Draw a picture of your observations.

What’s going on?

In your experiment, it should have been readily apparent that the more organized and uniform straws were much stronger than the randomly arranged ones. Your own bones have a similar pattern in their soft, spongy part called cancellous bone. This portion of bone has a honeycombed structure which makes the bones very strong, but relatively light.  The tiny tubes that make up the honeycomb are called the Haversian system and the actual tissue of the structures is made up of collagen. This allows them to maintain flexibility, but they are still composed of minerals – notably calcium and phosphorus which give them their hardness and strength.

Exercises

1. Name some of the parts that make up our skeletal system.
2. What is the smooth, hard, protective layer on the outside of bones called?
3. What is the inside spongy, porous, honeycombed bone called?
4. What is the network of tubes inside bones called?

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