Source: Images and Video Created by Amanda Soderlind
In this lesson today we're going to discuss the two divisions of the skeletal system, which are the axial and appendicular skeletons. So we're going to start with the appendicular skeleton. And the appendicular skeleton are bones of the limbs, hips, and shoulders. So basically, if you think of any body part that is a hanging body part, that would be part of your appendicular skeleton.
And your appendicular skeleton is kind of broken down into two sections as well. We have our pectoral girdle and our pelvic girdle. So the pectoral girdle includes bones of the upper body that are part of the appendicular skeleton. So that includes our scapulas, clavicles, and our upper limbs, so the parts of our upper body that hang. Our pelvic girdle are the bones of the lower body that are part of the appendicular skeleton. So that includes our pelvis and our lower limbs.
So everything that's highlighted in purple here on our skeleton is an example of bones of the appendicular skeleton. So again, they're the body parts that if you think of it as the hanging body parts, our limbs, our arms, our legs, and then our pelvis as well. So the pectoral and pelvic girdle are the two divisions of our appendicular skeleton. So up here is the pectoral girdle. And below is the pelvic girdle. So that's our appendicular skeleton.
The other division of our skeletal system is our axial skeleton. So let's take a look at that. And our axial skeleton includes the bones of the skeleton that compose our vertical axis. So if you think of a person standing up, your vertical axis is the up and down axis. So the bones that compose that axis are your skull, backbone, ribs, and sternum.
So that's highlighted in our skeleton here in green. So this is all part of our axial skeleton. And we're going to talk a little bit more in depth about some parts of our axial skeleton.
So let's start by talking about our backbone. So I have a picture here of our backbone. And we're going to identify the different segments of the backbone.
So first of all, I want to say very briefly that each one of the bones of our backbone is called a vertebra. But if we're talking about more than one, we call them vertebrae. So there are a total of 33 bones, 33 vertebrae in our spine. And those 33 bones are broken down into a couple different categories as you'll see here.
So the top part of our spine here is composed of our cervical vertebrae. And these are basically the bones that make up our neck. And there are seven of them. So those are our cervical vertebrae.
Our next section of bones are our thoracic vertebrae. So those are right here. So you'll notice that's a pretty big chunk right here. And that's a total of 12 bones that make up this section. And that's actually most of the part of your back is made up of this part of the spine.
Our next section is our lumbar vertebrae. So that's your lower back would be this section of your spine, the lumbar section. And that's made up of a total of five vertebrae.
Then following that, we have the sacrum. And the sacrum is made up of five bones. However, all five of those bones are fused together. So this is getting down closer to your tailbone, underneath your lumbar, the very, very, very lower part of your back.
And then after that, we have the coccyx. And the coccyx is made up of four bones, again, like the sacrum, all of which are fused together. So these are the different sections of your spine.
And in between each of the bones of your spine, you have these disks that are made of cartilage. So it's actually a cartilaginous joint in between each of these bones. And that cartilage helps provide cushion between the bones so there's not friction when those bones are rubbing together. And the main purpose of your spine is to give your body that structure and support, and also to protect your spinal cord.
So let's take a look at another type of bone found in our axial skeleton, which is the skull. And the skull is actually made up of over two dozen bones. And all of these bones are fused together by something called sutures. So you'll notice these little lines drawn around the skull separate all of the different types of bones of the skull.
And again, this is type of joint that forms between the bones. However, it's not a type of joint that generally allows for movement. It's just a type of joint that holds those bones of the skull together. And the purpose of the bones of your skull is to protect your brain and also to shape your face. So the way that those bones are fused together gives your face its shape.
And then we'll move on and talk about the ribs and the sternum here. So the ribs and the sternum, the purpose of them is to protect your internal organs. And you actually have 12 pairs of ribs that all attach to the spine. And the first couple ribs are actually going to attach to your sternum in the front.
So they're all fused to the spine and the back. And then you have some that attach to the sternum in the front. So again, the purpose of this is to protect the internal organs so you have something hard around those internal organs in order to be able to protect them.
So this lesson has been an overview on the structure and function of the axial and appendicular skeleton.
The division of the skeletal system that includes the bones of the hips, shoulders and the limbs.
The bones associated with the lower part of the appendicular skeleton including the pelvis and legs.
The bones associated with the upper part of the appendicular skeleton including the scapulas, clavicles and arms.
The division of the skeletal system that composes the body's vertical axis and includes the skull, backbone, ribs and sternum.
A part of the axial skeleton that acts to protect the brain.
A part of the axial skeleton that protects the spinal cord and gives shape and structure to the body.
Bones of the axial skeleton that attach to the sternum and backbone to compose a "cage" that protects internal organs.
A bone of the axial skeleton that serves as an attachment point on the front of the body for the ribs.