All right, so now that we've moved from the skull and the facial bones, we want to look at the other bones of the axial skeleton. This is going to include the hyoid bone, which is a bone in the throat. This is actually the only bone in the body that doesn't articulate with another bone, but it sits right above the larynx and it is for attachment of the tongue muscles.
Then you have the vertebral column. or the spinal column, as it's sometimes known, the backbone, the spine. The spinal column is divided into five regions, and it has some normal curvatures. It has a cervical curve, a thoracic curve, and a lumbar curve.
And then sometimes the sacral curve, it's referred to as the scapegrum, but there is a little curve there. You have a total of 26 vertebrae divided into five regions. The cervical vertebra is in the neck, and there are seven cervical vertebrae.
The thoracic vertebra goes through the torso, the thoracic region, and there are 12. The lumbar region is the lower back. There are five. Then the sacrum and the coccyx are fused. You have five bones fused as the sacrum, four fused as the coccyx.
They help support the body. They serve as an attachment point for the ribs, and they also protect the spinal cord. Now, between the vertebrae, you have intervertebral discs.
And these are rings of cartilage. On the outside, you have this fibrous ring called the annulus fibrosus. On the inside, you have this soft, liquidy, pulpy nucleus called the nucleus pulposus.
And then the top and the bottom of each disc is made of cartilage. The function of these discs is to set between the vertebra, the bones of the vertebra, so that they absorb the shock. They're kind of like shocks in your car and creating a little space between the vertebra. Now the vertebra themselves have very general forms that are consistent through most of the different vertebra.
First you have the body, which is this main portion, and you can see that's the part that stacks. Then you have these transverse processes that extend this way laterally. You have a spinous process, and you can see that here sticking out.
So if you feel down someone's back and you feel the bumps, that's the spinous process. And then the transverse processes are going this way. You have the intervertebral discs. And then you have an intervertebral foramen, which is a hole here where spinal nerves exit.
So at each level of the vertebra, you're going to have a pair of spinal nerves going out each side. Then right in the very center is the vertebral foramen. And this is where the spinal cord extends through the spinal column.
Okay. Now, if you look at each division of the vertebra, if you see a vertebra out of the spinal column, you can really kind of tell which portion it goes to because each area or region of the spinal cord vertebra have different characteristics. So if you look at a typical cervical vertebra, remember there are six of them, you will have transverse process, which is this opening here on the sides for spinal nerves.
that go through this transverse foramen. And you have a small body compared to the other vertebra. And the spinous process is what we call bifid or bifurcated.
You have two little bumps in the spinous process. Now, specifically, there are two of the cervical vertebra that are distinctly different. The first one is cervical vertebra number one.
It's called the atlas. The purpose of this top cervical vertebra is it's going to articulate with the occipital bone of the skull. So you have these flat depressions on the top called the superior articular facet, and those set in the depressions on the occipital bone on either side of the foramen magnum. Then you have an anterior and a posterior arch and a very elongated extended transverse process on the atlas.
Also, right here you see the dens. This comes up from cervical vertebra number two that I'll get to in a second. But this projection actually sets right here between the ligament on this anterior arch.
And it acts as a pivot point, allowing the head to turn or rotate around that little pole, if you will, called the dens. Notice that on cervical vertebra one, there's no spinous process and there's no body. cervical vertebra number two is called the axis and I think if you look at this one it looks a lot like that alien the little alien spaceships in Independence Day if you've ever seen that movie with Jeff Goldblum and Will Smith but you can see right here with that bin sticking up how it goes into the atlas but that looks exactly like those little alien spacecraft so it's really easy to identify that way Now the purpose of that DENS is to articulate in the anterior region of the atlas, and that allows the atlas to rotate right around the axis.
Notice that the DENS does have the bifurcated spinous process and a body, a small body, which is different than you see with the atlas. Now moving into the next region, you have the thoracic region. And in the thoracic region, the ribs are going to connect to the thoracic vertebra.
So you're going to see attachment areas for the ribs that you don't see in other parts of the vertebral column. You have a facet here for the tubercle part of the rib. You have a superior facet for the head of the rib and then a demi facet for the head of the rib, depending on where you are. And then the lumbar vertebra, these are the largest, there are five of them.
And so the body is very large on the lumbar vertebra because they have to support the weight of the whole upper body. Also notice the spinous process is rounded in the lumbar region. But other than that, there are no specific characteristics of your lumbar vertebra.
Then the sacrum and coccyx, these are fused bones. The sacrum is five fused vertebrae, and that actually forms the back of the pelvic girdle. And then, so the pelvic girdle is part of the appendicular skeleton minus the coccyx and the sacrum. So coming off the bottom of the sacrum is four fused bones called the coccyx, sometimes referred to as the tailbone.
And then the fused spinous processes here in the sacrum form what's known as the medial median sacral crest for attachment of muscles. On the anterior portion of the body, you have the sternum or the breastbone, and that's the flat bone right in the center of the chest wall. And it's divided into three sections, the manubrium, which looks like the knot of a men's tie, the body, which is the main portion, and then this little portion at the bottom called the xiphoid process, or some people refer to that as the Chuck Norris bone.
Because if you've ever seen martial arts, a defense technique is to come up with an uppercut in the center of the chest and it snaps off that xiphoid process with your heart sitting right underneath. So it's a it can penetrate into the heart and can be deadly. Also, with the sternum, you have costal cartilage here.
This is cartilage connected to the ribs. So that's how your ribs attach here to the sternum. So the ribs, their function is to support the thoracic cavity, but also to protect the heart and the lungs.
There are 12 pair of ribs. They have three distinct portions. You have a body and then a neck and then the head, and they're going to articulate with the vertebra. So you have a superior and inferior facet, and then an articular facet here that will articulate with this transverse process. Now, these are going to attach to the sternum via the costal cartilage.
The first seven ribs from superior to inferior, these are called true ribs, if you look here, because their costal cartilage connects directly to the sternum. The next ribs, eight through 10, are what we call false ribs because these their cartilage connects to the cartilage of the ones above, but doesn't connect directly to the sternum. And then you have 11 and 12, which are known as floating ribs, because they don't connect to the sternum with cartilage at all.