Anatomy and Physiology 1, Chapter 7, The Axial Skeleton. So in this chapter, we are talking about the axial skeleton in particular. So we're mainly going to focus on the bones that make it up, and then some highlights about those particular bones. What we are not doing in this chapter is going over the features of all the individual axial bones.
That is something that you will be doing during lab time in your anatomy course or my anatomy course if you're taking me. We'll be learning the bones of the axial skeleton as one of our first labs. So this is not going to be that, but will be an introduction to what makes it up and the important points that separate it from the appendicular skeleton.
So the axial skeleton is made up of the bones of the head and your trunk and forms the longitudinal axis of your body. So I like to think of it as your core or your axis, which makes sense. that its name is axial. The appendicular skeleton, which we will talk about in chapter 8, the one coming right after this one, is going to include the bones that support the limbs and then the limbs themselves. So that's what would hang off of the axial skeleton.
So here's a great picture of the skeleton in general. But the axial skeleton is colored in yellow here. So you can see that it does include the skull, the neck, and your trunk. So that would be ribs and vertebrae on down to the tailbone.
And you can see what is not highlighted in yellow is what would be considered the appendicular skeleton, which is your appendages or your limbs. Okay, so here's the axial skeleton removed from the rest of the skeleton. And again, reviewing, we have the skull, vertebral column, sacrum, and coccyx, as well as the ribs.
And we'll also include a bone called the hyoid, which is under the jaw here. We're not able to see it very well. and the ear bones which would be within the skull. So the axial skeleton has 80 bones total and they are going to include the bones of the skull, the bones associated with the skull which again are the auditory ossicles or ear bones, there are six of those, and the hyoid bone, the thoracic cage, which includes your sternum or breast bone and your ribs, the vertebral column, which includes the vertebrae, sacrum, and coccyx. And the functions of your axial skeleton is to support and protect the organs in your body cavities.
They're also going to be great points of attachment for muscles that are going to help to stabilize your head, neck, and trunk. They help you to breathe because we've got some connected to the ribcage. And they're going to stabilize parts of the other part of the skeleton called the appendicular.
So let's start with the skull. The skull has 22 bones and some of those make up the cranial cavity, which would be the top part of the skull that contains the brain. And there are facial bones that will protect and support entrances to your digestive and respiratory tract. So looking at this picture here, this would be the cranial bones that are found supporting and protecting the brain.
So again, when you work on your first lab, typically in anatomy one, you will be learning the bones and features of the skull. And here are the facial bones and these bones will help protect the openings to the digestive and respiratory systems. So near the skull or associated with it we have the hyoid bone which is this.
It's found in your throat area, neck, and then the three ear bones known as the auditory ossicles. You've got three on each side of your head so a total of six. and they are very, very small. So as this picture shows, they would easily fit on the surface of a dime. So we move down from the skull to the vertebral column, also known as the spine, and its job is to protect the spinal cord which runs through it.
And as you look at vertebrae during your first lab as well, you'll notice that there is an opening through the vertebrae called a foramen and those foramen vertebral foramen will allow the spinal cord to move through and they surround it so that gives them a great protection protection. They're also going to support the head and the body and there are 26 total bones that are considered part of the vertebral column. We have 24 vertebrae, the sacrum and the coccyx or tailbone. So in this figure we can see all of those bones.
We have the vertebrae. together which makes the vertebral column or spine and then we have the sacrum and the coccyx or tailbone. So we're going to look at some curves and also some regions of the vertebrae as well. Let's start with the curves.
We have the spinal curves which include cervical, thoracic, lumbar, and sacral. So let's start with the thoracic and sacral. So these two curves here. The thoracic and sacral curves are called primary curves, or accommodation curves, and they're primary, which means first, because they appear during your fetal development, so before you are ever born. you develop these curves and their job is to accommodate your internal organs.
So if we go back to look at the thoracic and sacral curves in our figure, so thoracic would be these here, the ones that have a T beside them. The thoracic curve again is primary and it gives room for your thoracic organs. So it curves outward there to give room.
for your thoracic organs, so things like the lungs and heart. The sacral curve, also primary, which would be down here within your pelvis, is going to provide room for various abdominopelvic organs. So you are born with both of these curves in place. The cervical and lumbar curves are called secondary or compensation curves. So these appear later, which is why we call them secondary.
They appear after birth and they will shift your body weight so that you can stand upright. So let's take a look at those cervical and lumbar. So starting with the cervical, these are the cervical vertebrae with a C beside them.
And this is going to develop. as the baby learns to balance the weight of his or her neck on the vertebrae. And then we have the lumbar curve, which is also secondary.
It's going to balance the weight of the trunk over the lower limbs. So this curve is what's going to help you to be able to stand. And so lumbar, these vertebrae are designated by L's.
So in the neck there are seven cervical vertebrae, upper back 12 thoracic vertebrae. These vertebrae are going to join or articulate with one or more pairs of ribs. Lower back has five lumbar vertebrae. So let's look at that again. And this is another thing you'll be looking at in your first lab.
So cervical or C's, there are seven. thoracic or T's there are 12 and then L's or lumbars there are 5 followed by the sacrum and coccyx. Now one way that I've heard, which is a great way to remember this, is we have breakfast at 7, 7 cervical vertebrae, we have lunch at 12, 12 thoracic vertebrae, and we have dinner at 5, lumbar 5 vertebrae.
Okay, so the sacrum, which is underneath the lumbar vertebrae, these are curved more in men than in women. The sacrum is going to protect your reproductive, urinary, and digestive organs and will attach the axial skeleton to the pelvic girdle. So the pelvic girdle is what's going to help us to make a pelvis. because right now we're just talking about the sacrum.
So we'll talk about that a little bit more in the appendicular chapter. But it's going to attach us to the rest of the pelvis and also allow broad muscles to attach that help to move our thigh. So here is the sacrum. This is from the back or posterior view. And you can see underneath it, this is the coccyx or tailbone.
So going back up to the chest, the thoracic cage, also known as the rib cage, the skeleton of the chest is made up of thoracic vertebrae, ribs, costal cartilage, and the sternum or breastplate. So taking a look at that, so our T or thoracic vertebrae are running down like so. Some of them are obscured by the sternum.
We see the sternum or breastbone right up front. And then coming off of it, of course, are the ribs. Now these darkened areas here, this represents costal cartilage.
And this cartilage helps to give a little flexibility to the rib cage, especially as we are inhaling and exhaling. Here's the same rib cage from the back, so you're able to see thoracic all the way down and how the ribs originate off of those thoracic vertebrae. So the function of your thoracic cage is to protect your thoracic cavity organs, and so this is going to include thymus, heart, and lungs. It also allows for muscle attachment involved in breathing. keeping the position of the vertebral column and moving pectoral girdles.
Now we haven't talked about pectoral girdles yet, but we will shortly when we get to chapter 8. But the pectoral girdles are your shoulder girdles or the bones that attach your arms to the rest of your body or to your core. So we'll go over those. So the ribs and the sternum together form the rib cage. The ribs, there are 12 pairs of long curved flat bones, which we call the ribs, extending from the thoracic vertebrae. Okay, so that is going to finish up what belongs to the axial skeleton technically, and that will bring us straight towards chapter 8 where we will classify the rest of the skeleton, which is the appendicular.