Hello and welcome. It's now time to learn about the skeleton. The skeletal system consists of the bones, cartilages, joints, and ligaments of the body. But in this unit, we are really going to focus and learn about those bones. We're going to start off just by saying that there are 206 named bones in the body, and we are going to learn the names. But that number, 206, is a number you should remember. It's a really easy test question to ask, and if you remember 206, it's a really easy test question to get right. The number 206, though, is a bit more of an estimate, really. We're going to say that the exact number varies by age, and by age, it can vary a lot. You're born with more than 206 bones. You're born with well over 300 bones. And as the skeleton grows and develops, some of those smaller bones grow and fuse together to make the larger bones of the adult skeleton. But it also varies in adults by individual. Some people just have more bones than other people. Sometimes those smaller bones will fuse together in one person and they'll remain separate bones in another person, or sometimes small bones will develop in one person that don't develop in another person. That's especially true for the sesamoid bones that are sometimes in people's hands and feet. And then finally, some people develop bones like an extra set of ribs or an extra vertebrae. Now that's a bit more rare, but that's a part of normal human variation. And it really means that that 206, while you should remember that number, it's a bit more of an estimate.
We're going to break these 206 bones up into two major categories. The first category is going to be the axial skeleton. Your axial skeleton is going to include your skull, your spinal column, and your ribs. And by that, I'm really meaning the rib cage, including the sternum. We can look over here in our anatomical model. We see an anatomical model showing the full skeleton, and you can see in blue that axial skeleton. That axial skeleton being the skull, the rib cage, and the spinal column, including the sacrum down there at the bottom. The axial skeleton is there to provide structure for the body. Your body, the core of your body, has its shape because of those bones. But it's also doing a lot of protection for internal organs. The skull, the rib cage, and the spinal column all have very sensitive organs inside of them that they are protecting.
The second large group of bones that we're going to learn is going to be the appendicular skeleton. The appendicular skeleton refers to your appendages, your arms and legs. So that's going to be your limbs plus the pectoral and pelvic girdles. Now you may not have heard of the girdles before. A girdle is just something that surrounds something or binds something else. So as we look over at our anatomical model here, well, we can see the bones of the arms and legs there, but then we also have these girdles. And that's going to be things like the shoulder blade and the collarbones up there and the hip bones or the coxal bones down here. Those girdles attach the arms and legs to the axial skeleton. The appendicular skeleton is really there to provide movement. This is how you get around in the world.
Now, I just want to again go back to this number 206. 206 sounds like a lot of bones to learn. It is. But don't worry too much. It's not actually 206 names of bones that you have to learn. For example, there are 80 bones in the axial skeleton, but 24 of those are ribs and another 24 of those are vertebrae. So that's 48 bones. That's more than half the bones in the axial skeleton, right there, and we're not going to learn individual names for each one of those. We're going to learn to put them into groups. Similarly, for the appendicular skeleton, we have 126 bones, but every single one of those bones has a right and left, so we can cut that number right in half right away. There are also groups of things. Like, we're not going to learn an individual name for every finger or toe bone. We learn to group them. Now, to make it a bit more complex, we are going to learn some major features on some bones, some of the lumps and bumps of the bones, and that's going to bump that number of things you've got to learn back up a bit. But don't worry, we'll get you there. Finally, I just like to say when we're learning the skeleton, this more than any other unit in this course, we're learning about the human body and you have a human body. You can feel most of your bones. So as you learn the bones, figure out how they fit in your body. Feel your own bones. As you learn about a lump or a bump of a bone, feel it. Find out where it is. It is not cheating on a test to take a second and feel a bone in your leg or in your arm, and make sure that what you're seeing on the page is matching up to what you feel in your body.
With that, let's go learn some bones.
