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All About Skeletons

Contributor: Nicholas Bongio. Lesson ID: 13060

Did you know skeletons are alive? It is not a scary story; it's true! Learn all about your skeleton and how it compares to the skeletons of other animals!


Life Science

learning style
personality style
Grade Level
Middle School (6-8)
Lesson Type
Dig Deeper

Lesson Plan - Get It!


Did you know that you are constantly destroying your skeleton and rebuilding it? The inside of your body is a constant construction site! Specialized cells tirelessly work on your bones every day maintaining the shape that makes you you, and keeping you healthy. They replace your entire skeleton every 10 years!

Other creatures have skeletons that are amazingly similar to yours, with some modifications. Some animals, though, keep their skeletons on the outside of their bodies while others move around just fine with no skeleton at all!

Let's learn how your amazing worker cells keep you standing tall with healthy bones, and how other creatures provide structure in their own ways!

The Skeleton

Your skeleton is a structure made primarily of collagen and calcium that has its plans laid out in your DNA. You have what's called an endoskeleton, or internal skeleton. The genes you got from your parents determine, along with the environment, how tall you will be and the shape of your face and body.

If you want to know more about the different bones in the human body, check out the Elephango lesson under Additional Resources in the right-hand sidebar.

Comparative Skeletal Anatomy

All animals with endoskeletons have similar bones. The shape and number of their bones are the major difference between them. Check out the image below showing the limbs of a human, dog, bird, and whale. You should be able to spot some similarities between all four. Basic differences in the way we build bones are what make animals different shapes.

homology of 4 vertebrates

Image by Boπkob BπaAncπab Πetpobny, via Wikimedia Commons, is licensed under the CC BY-SA 4.0 license.

As you can see, we all have similar bones inside. They are just stretched out in different shapes. Even if an animal uses a limb for the same thing, say for flying, it may be radically different. Read Human, Bird, and Bat Bone Comparison, by Elizabeth Hagen at Arizona State University School of Life Sciences Ask A Biologist, to see how different bat and bird wings are inside!

Animals can also build bones differently on a microscopic level. You may have heard that bird bones are hollow. Actually, all animal bones have "hollow" spaces inside. These areas are filled with important cells for your body, like cells that make blood cells and bone-producing cells that you will learn about next. One thing that can be different, however, is the structure of those hollow spaces. For example, bird bones are structured differently for flight. Check out Bird Bones May be Hollow, But They are Also Heavy, Says UMass Amherst Biologist (University of Massachusetts Amherst News & Media Relations) to learn the truth about birds and their "hollow" bones.

How Bones Are Built and Maintained

Your bones aren't permanent, unchanging structures inside you. They are living things! Whether you're still growing or not, you have little builder cells working hard to keep your bones healthy and in just the right shape to maintain your body. If they didn't maintain things, you might get osteoporosis like the image below. This happens when your bones don't quickly replace minerals that are lost, and they become brittle.

osteoporosis bone

Luckily, as long as you're healthy, there are three types of cells to patch your skeleton up! These all begin with the prefix osteo- because that stands for bone!

Scientists continue to study bone regeneration in search of new ways to heal people. The male deer is a champion bone-builder that sheds its antlers every year and re-grows them the next year super-fast! Read Antlers Are Miraculous Face Organs That Could Benefit Human Health, by Jason Bittel at Smithsonian.com, to see how scientists are studying deer.

Muscle Attachment and Movement

The bones in your body provide places for muscles to attach to allow movement. Bones are all attached to two different muscles, so they can stretch and pull to move the bones.

Get a brief introduction to skeletal muscles from Science - Bones and Muscles by Designmate Pvt. Ltd. - Official:


That's all pretty amazing, right? Well, not every animal with a skeleton likes to do things that way. There are also...


Some animals don't like their bones on the inside, so they have an exoskeleton. An exoskeleton is a skeleton on the outside of the body. Insects and crustaceans all have an exoskeleton that consists of hard plates covering their body. Instead of collagen and bones, however, their skeleton is made from chitin, which is a polysaccharide, or a long chain of sugar. Don't try eating them though! Our bodies can't break this type of sugar down.

Insects and crustaceans can produce chitin on the surface of their bodies when they are growing. Each time that they grow, they shed their old skeleton and build a new squishy exoskeleton! Sclerotin makes it harden when they have expanded to a larger size.


Hydrostatic Skeletons

Some animals don't have a solid skeleton at all, such as earthworms. Instead, they use the power of muscles and water pressure to move their squishy bodies around! Muscles squeeze fluid from one part of the body to another in order to push the body into other shapes, to extend, or contract. Check out a worm next time it rains, and you'll be able to observe this cool form of movement!


Now that you've got the low-down on our skeleton and the different types out there, head to the Got It? section to explore more!

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