Skeleton Facts

Skeletons ['skĕl-ə-'tŭnz]

Connected groups of bones that help shape and support animal bodies.

Halloween spooky costume, skeleton

When some people think of skeletons, they think of Halloween or some mad scientist's display in a laboratory. But we all have a skeleton. It is what gives our bodies shape and form. Without a skeleton, we would be a heap of skin and muscles - like jellyfish! Our skeleton allows us to walk across a room, twist our heads from side to side, toss a ball and type on a keyboard.

The skeleton is made of a series of bones. The key feature of animals with internal skeletons is that they have a set of bones known as vertebrae which are located along the spine. Vertebrates are animals that have a backbone inside their bodies. Animals without a backbone are called invertebrates.


Bone and skeleton

So what are bones? Bones are largely made of calcium and other minerals. They are strong enough to support our weight and our movement. Bones protect our major organs (such as lungs, heart and brain) and give our bodies shape. Our skeleton can be categorized into two parts. The axial skeleton contains the ribs, skull, and spine, and its purpose is to keep us upright. The appendicular skeleton is comprised of the bones in our arms, legs, shoulders and hips, and its purpose is for movement.

Bones in our bodies are very much alive. Most bones have four layers: the outer layer is the periosteum, and the next layer is hard, compact bone. Inside this is a layer of lighter, spongy bone called cancellous bone. The innermost part of the bone is the jelly-like bone marrow, where new red and white blood cells are constantly being produced for our bodies.


In children, bones are continually growing and changing. A baby is born with 300 bones. Over time, some of those bones join to make larger bones. The adult human body has 206 bones which make up the skeleton. Almost half of these are in the hands and feet! In fact, the area of the body with the most bones is the wrist, hand, and fingers, where 54 bones are found. The largest bone in the body is the femur or thigh bone. The smallest is called the staples or stirrup, found in the inner ear. It is only .11 inches (2.8 mm) long.

Contractor with Concrete Block

Although our bones stop growing around the age of 20, new bone cells are constantly rebuilt throughout our lives. Did you know that our bones are stronger than concrete? There are very few substances that can compare with the lightness and strength of bones.

How We Move Our Bones

A model of a human knee

Our bones are not able to move on their own. They require something to pull them in order to be useful. Attached to many of the bones are tough, white bands known as tendons. Tendons do not have any blood vessels and so take a long time to heal if damaged.

Tendons connect bones to muscles. Muscles contract and relax as needed to help our bones move, as well as the arms, legs, feet, and back they support. Learn more about how muscles work at the Science Trek: Muscles page.


Concentrated kid examining his damaged elbow joint

The place where two bones meet is called a joint. Some joints, like those in the skull, don't move at all. But other joints allow us to bend, twist, and move different parts of our bodies. One type of moving joint is called a hinge joint, found at our elbows and knees. These joints let us bend and straighten our arms and legs. Another type is the ball and socket joint, found at our shoulders and hips. These joints allow for movement in many directions. Bones are held in place at joints by tissues called ligaments.

The special connections between the bones are covered with a plastic-like material called cartilage. Cartilage protects the end of the bones from rubbing together. Cartilage also makes up our outer ears and the end of the nose, which is why we can bend our ear without a bone breaking. The bones, joints, tendons, ligaments, and cartilage together make up the skeletal system.


X-Ray film scan of human

Our heads contain a special set of bones and plates known as the skull bones. Some of our skull bones protect our brains, while others make up the structure of our faces. When a baby is born, there are spaces between the bones of the skull. As we grow, the spaces between the bones close up. Without this unique system, the skull bones would collide with each other as they grow. The joints that connect bones in our skulls, known as sutures, are not moving joints. In fact, the jawbone is the only bone in our heads that we can move.


The animals known as vertebrates include mammals, fish, birds, reptiles, and amphibians. Each of these animals has a backbone and a skeleton. Birds have bones that are hollow — this makes their bones lighter for flight.

Frog skeleton, studio shot


While vertebrates all have skeletons to give their bodies shape and support, invertebrates have no bones. Many invertebrates have an exoskeleton, or a hard outer shell, to provide protection and support like bones do.

Closeup shot of a lobster on the sand in the ocean water

Insects, crabs, lobsters, and shrimp are a few of the creatures with exoskeletons. Other invertebrates are soft like the octopus, squid or earthworm.

Taking Care of Bones

Our bones are remarkably strong, but they can be broken or fractured. If that happens, bones will heal on their own. Because bones are made of living cells, when a bone is broken it will produce new cells to rebuild the bone. A doctor will make sure the bone mends correctly by using a cast or sling to keep the bone in place while it heals. It can take a long time for the bone to be back to normal, so it's important to take care of our bones to prevent injuries. Our skeleton supports us every day, so we need to be good to our bones!

  • Keep the skeleton strong by drinking milk and eating calcium-rich foods like cheese, yogurt, and dark green vegetables. Calcium helps bones become hard and strong.
  • Wear a helmet when bike-riding. Wear protective equipment for sports such as football, soccer, lacrosse, ice hockey, horseback riding, and skateboarding.
  • Bones need exercise to stay as healthy as possible. Running, jumping, walking and dancing are all weight-bearing activities that are good for bones.
Portrait of Asian little cute kid holding a cup of milk feel happy enjoy drinking milk at home.

Top 10 Questions

October 2011

Thanks to Dr. Jeffrey Shilt, Director of Pediatric Orthopedics, St. Alphonsus Regional Medical Center; Benjamin Davis, Microgravity Researcher, Boise State University; and Dr. Jeff Seegmiller, Assistant Profess for the answers.

  1. How long does it take for a leg bone to be repaired?

    For most of us it takes about six to eight weeks for bones to heal. It can take longer if it's a more complicated break (more pieces to the fracture or more bone pieces to heal), or for people who are older. (From Chloe in Mrs. Schweitzer's class at Riverside Elementary School in Boise)

  2. Why do bones pop out of their sockets?

    Usually it's because a person has experienced a force that is beyond the capabilities of their joint. When this happens, their bone pops out because it can't handle it anymore. (From Adam at Dalton Elementary School in Dalton Gardens)

  3. What is the strongest bone in the human body?

    There's no specific answer to that question. It actually differs as you age and depends on how much stress is formed on each part of the body. Certain bones will bear a lot of weight or tension. Therefore a lot of bones are strong enough for the amount of work they are doing. Bones are dynamic, living and growing, so it all depends on each person's body and the particular work their bones are doing. (From Justice in Mrs. Hunt's class at Cynthia Mann Elementary School in Boise)

  4. Why do we have marrow in our bones?

    Bone marrow provides the source for all the cells in your body that go on and produce other tissues. It gives you all the important cells in your blood stream, and it also provides the basis for cells that help produce the tissues, all the musculoskeletal tissues that you have. It is very important. (From Cooper in Boise)

  5. What is bone tissue made of?

    It is the outer shell of the bone comprised of connective tissue. It provides the internal support of the body. It differs from bone marrow in that the marrow is in the center of the bone. (From Casey at Dalton Elementary School in Dalton Gardens)

  6. How do kids like me sprain their ankles?

    When ankles get sprained, you end up hurting a ligament. Ligaments are what hold the bones together. When you land on something you are not expecting, you may roll the joint farther than it was expected to roll. This puts too much stress on the ligament and the ligament ends up getting hurt. (From Sydney at Dalton Elementary School in Dalton Gardens)

  7. Which bone in your body is the most important?

    It all depends on what you like to do the most. Your skull and vertebral column are very important because they protect your central nervous system and allow you to do all of the complicated things you do. However, if you like to dance, you may be a big fan of the femur and the hip socket. If you are more interested in spelling bees, you would be appreciative of your skull for keeping your brain intact. Teeth are also very important, so as you can see, there are a lot of choices for which is the most important bone. (From Katherine in Mrs. Schweitzer's class at Riverside Elementary School in Boise)

  8. How does the skull move?

    The skull bones move very little. We call the joints on the skull, sutures, and they move a very small amount in response to trauma or to swelling in the brain. If you are referring to how your head moves in relation to the rest of your body, you need to look at the two bones that are closest to the skull at the top of the spinal chord. These bones allow for all of the movement that we are able to achieve. (From Gabe in Mrs. Hunt's class at Cynthia Mann Elementary School in Boise)

  9. What is the smallest bone in the human body?

    The smallest bone is the stapes, and it is located in the ear. (From Michael in Mrs. Boehne's class at McDonald Elementary School in Moscow)

  10. How many bones are there in an average ten-year-old girl's body?

    We have 206 bones. However, before we fully mature, some of those bones are actually in parts, held together by cartilage. Sometimes they may count as even more bones, so younger children may have more bones than adults. (From Chloe in Mrs.Boehne's class at McDonald Elementary School in Moscow)