Here are 6 interesting things you might not know about the human skeleton

Bones are really cool. When people learn that bone is a living tissue, they are often surprised. Most people know that our bones can heal themselves after they break or crack.

But they are also constantly tearing themselves down and putting themselves back together as a result of the things they do every day. This is a cellular process called remodelling.

Here are some more things you should know about skeletons.

1. Everyone doesn’t have 206 bones

The average number of bones in a human skeleton is 206, which is taught in school. But babies are born with more than 300 bones that are made of cartilage. During the first few years of life, the cartilage turns into bone, and some bones join together.

Some people are born with extra bones, like a 13th set of ribs or an extra finger. During their lives, some people even get extra bones.

A recent study showed that the fabella, a small bone in the back of the knee that looks like a bean, is becoming more common because people are eating better and getting heavier.

2. The height of the human skeleton is always changing

The most rapid growth in height happens in a child’s first year, and by the time we are in our mid- to late-teens, we have reached our adult height. But our height can still change even after our bones stop growing.

At joints, where two bones meet, cartilage covers the ends of the bones. Cartilage is a layer of rubbery cells, collagens, proteoglycans, and water.

Gravity pulls down on your cartilage throughout the day, especially in your spine. This means that by the time you go to bed, you have shrunk. After lying flat for a while, the cartilage is able to grow back to its normal size.

Astronauts are up to 3 percent taller after a trip to space because the lack of gravity makes them grow.

And it’s not just the cartilage. When you hit something, the bones themselves get shorter. Scientists have found that when running, the tibia (shin bone) shortens by a millimeter when it hits the ground.

3. Only one bone isn’t connected to another bone

The thigh bone is attached to the hip bone. But not all of the bones in a person’s skeleton are connected. The hyoid bone is the only one that’s different.

The U-shaped hyoid bone sits at the bottom of the tongue. Muscles and ligaments from the base of the skull and jaw bones above hold it in place. This bone lets people (and our Neanderthal ancestors) talk, breathe, and swallow.

Rarely does the hyoid bone break, and if it does, it could mean that the person died from being strangled or hung.

4. Bone marrow is more than just filler

Bone marrow is made up of fat cells, blood cells, and immune cells. It is found in long bones like the thighbone.

When a child is young, the bone marrow is red because it makes blood cells.

In an adult, the bone marrow is yellow and has 10% of the body’s total fat. Long ago, people thought that the fat cells in bone marrow were just there to take up space. Now, scientists are learning that the fat inside bones has important metabolic and endocrine functions that affect the whole body.

5. The ear has the fewest bones

The malleus (hammer), the incus (anvil), and the stapes are the three smallest bones in the body (stirrup). The group of these bones is called the ossicles, which comes from the Latin word for “small bones.” Their job is to send vibrations from sound waves in the air to the fluid in the inner ear.

Not only are these the smallest bones in the body, but they are also the only ones that don’t change after the age of one. This is important because a change in shape could make it harder to hear.

The ossicles are also important in the fields of archaeology and forensics. Because our bones are made while we are still in the womb, isotope analysis can tell us about the diet and health of the mother.

6. Bones cause you stress

The sympathetic nervous system is the part of the human body that prepares the body for intense activity. This is sometimes called the “fight-or-flight response,” and it happens when the hormone adrenaline is released in response to stress.

But recently, scientists published a paper saying that osteocalcin, a hormone made by cells that make bone, is a key part of the body’s stress response.

Compared to regular mice, mice that were bred to not be able to make osteocalcin did not have a fight-or-flight response when they were suddenly stressed.

The scientists also looked at the levels of osteocalcin in humans. When the humans were stressed, the levels of osteocalcin in their blood and urine went up. In the end, it was shown that osteocalcin turns off the parasympathetic “rest and digest” system, allowing the “fight or flight” response to be activated.

We’ve known for a long time that the skeleton’s physical job is to protect the body. For example, the ribs protect our most important organs. So maybe it shouldn’t be a surprise that our bones also help keep us safe in a physiological way.