 This video will cover part 3 of the axial skeleton. As we go, we'll cover the following study objectives. Discuss the vertebral column and regional variation in its bony components and curvatures. Describe the components of the thoracic cage. Here we see the vertebral column, which consists of 26 bones, which are medium to small in size and have an irregular shape. It's located along the midline from the base of the skull to the pelvis and contains the vertebral cavity protecting the spinal cord. There are 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, 1 sacrum and 1 coccyx. The curvatures of the vertebral column are the cervical, thoracic, lumbar, and sacral curves. At birth, there are only curvatures present in the thoracic and sacral regions. These are known as the primary curves. Secondary curves develop with upright posture. These are the cervical and lumbar curvatures. Here we see abnormal curvatures of the vertebral column and abnormal lateral curvature is known as scoliosis and exaggerated thoracic curvature is known as kyphosis, commonly referred to as hunchback, and exaggerated lumbar curve is known as lordosis, commonly referred to as swayback. In this illustration we see the parts of a typical vertebra, typical vertebral bone has a body, this large region here, the body is found on the anterior and then on the posterior there's a spinous process that points to the posterior and there are two transverse processes that extend out laterally. Extending from the superior and inferior surfaces are articular processes and a facet is the articular surface where the joint is formed between superior and inferior articular processes. Here we see an inferior articular process that is forming a joint with the superior articular process of the next vertebrae below it and the facets are the surfaces where the articular processes fit together to form a joint. There are also intervertebral discs where the adjacent vertebral bodies articulate. The intervertebral disc contains a pad of fibrocartilage in order to prevent the vertebral bodies from contacting one another and to absorb the shock of our body weight that's placed on the body of the vertebrae. In the center of the vertebrae is the vertebral foramen which is surrounding the spinal cord so the vertebral cavity is the space inside of the vertebral foramen where the spinal cord is traveling, is protected. The vertebral arch extends from the body as pedicles extending to the posterior and then lamina extend around to join the spinous process. So here we can see lamina are coming together into the spinous process whereas the pedicle extends from the body over to the transverse process. The lamina extends from the transverse process over to the spinous process. In this illustration we can see the articulation of adjacent vertebrae where there's an intervertebral disc. The intervertebral disc shown in blue here consists of an outer ring of fibrocartilage called annulus fibrosis. The annulus fibrosis surrounds a jelly-like core of loose connective tissue called nucleus pulposus. Annulus fibrosis contains the nucleus pulposus and is a strong fibrous cartilage, a pad of fibrocartilage that can absorb the shock of the body. However, it is possible for the annulus fibrosis to rupture and nucleus pulposus to slip through annulus fibrosis and this is the condition known as a slip disc. We can also see here the intervertebral foramen. The intervertebral foramen is an opening between adjacent vertebrae and between the lamina of adjacent vertebrae where the spinal nerves travel out from the vertebral cavity. The spinal nerves traveling in and out of the spinal cord are traveling through the intervertebral foramen. Here we see the characteristics of a typical cervical vertebrae. There are seven cervical vertebrae which are numbered 1 through 7 starting with the most superior C1 to the most inferior C7. Cervical vertebrae typically have a split tip to their spinous process known as a bifid spinous process. The body of the cervical vertebrae is relatively small and the vertebral foramen is relatively large. There's also transverse foramen in the transverse process of a cervical vertebrae where the vertebral arteries and vertebral veins are traveling up and down from the brain. The first two cervical vertebrae are specially named as well as the seventh cervical vertebrae. C1 is atlas named after the Greek titan that was holding the heavens on his shoulders. Axis is C2 and we'll see that axis provides an axis of rotation for the atlas and the head superior to atlas to form a pivot joint allowing the head to rotate to allow the neck to rotate to the left and to the right whereas atlas will enable the head to flex and extend as if you were shaking your head to say yes. Axis allows pivoting as if you were to shake your head to say no. And C7 is known as vertebra prominence and C7 has the unique features of a longer spinous process and it's a bifid spinous process, the tip is not split and so C7 resembles the spinous process of a thoracic vertebrae more than the spinous process of the C1 through C6. Here we see atlas C1 from the superior view. Atlas is unique in that it does not have a body and instead of having a spinous process we just have this posterior arch. The axis on the right here we can see has a feature known as the dens or adontoid process. The dens provides an axis of rotation in order to allow movement of the head and atlas to rotate to the left and to the right. And so dens develops from what would have been the body of atlas the precursor to the body of atlas instead fuses to the body of axis forming dens the adontoid process that serves as the axis of rotation. Here we can see the ligaments that extend from the occipital bone from external occipital protuberance and the nucleolines down to the spinous processes of cervical and thoracic vertebrae. The elastic ligaments extending to the spinous processes of cervical vertebrae and attaching to the occipital bone along the nucleolines and external occipital protuberance that these elastic ligaments produce a force to help extend the neck to help hold the head upright. Here we see a illustration of the thoracic vertebrae. A unique feature of the thoracic vertebrae is that they have costal facets. The costal facets, superior and inferior costal facets are the surfaces that articulate with the ribs. And so a unique feature of the thoracic vertebrae is that they form articulations with the ribs and have costal facets. They also have long slender spinous processes. You can see they're pointing inferior and they're long and slender. So that's another distinguishing feature of the thoracic vertebrae. They have a medium sized body and the vertebral foramen is also intermediate in size. So in contrast we'll see the lumbar vertebrae have a large body with a small vertebral foramen and the cervical vertebrae have a small body with a relatively large vertebral foramen. Here we see an illustration of lumbar vertebrae. The characteristics of lumbar vertebrae include a massive, very large and oval shaped body and the spinous process is a blunt square shape that points straight posterior. So you can see here the lumbar vertebrae have their spinous process pointing straight posterior whereas most of the thoracic vertebrae have the spinous process pointing inferior and the vertebral foramen is relatively small. In the lumbar region the spinal cord is more narrow and as more spinal nerves attach to the spinal cord the diameter of the spinal cord increases towards the cervical region and for that reason the vertebral foramen has a relatively large diameter in the cervical region and a relatively small diameter in the lumbar region. Here we see the sacrum and coccyx. The sacrum forms from five sacral vertebrae and these sacral vertebrae fuse together after puberty to form one sacrum. The base of the sacrum is the superior wider region and the apex is the narrower inferior region. The sacral promontory is a ridge on the anterior rim of the base and is used as an internal landmark for pelvic exams. The sacral canal travels down through as a continuation of the vertebral foramen and contains a bundle of spinal nerves that are traveling down through and spinal nerves extend out through sacral foramina. So here we can see the posterior sacral foramina and the anterior sacral foramina where spinal nerves extend out. There is a ridge on the posterior of the sacrum known as the median sacral crest. So here we can see median sacral crest is essentially the fused spinous processes of the sacral vertebrae and then inferior to the apex of the sacrum is the coccyx, our tailbone, made of three to five small vertebrae which fuse together later in life. Here we see an image of a herniated intervertebral disc or a slipped disc where the nucleus pulposus, the gelatinous inner portion of the intervertebral disc ruptures through the fibrocartilage of annulus fibrosis and this slipped disc can compress a nerve in the intervertebral foramen. This can lead to excruciating pain and loss of function for the area, the muscles that are served by this nerve. Slip discs are more common in the lumbar region where there's greater force of our body weight pressing on the intervertebral disc and the disc can wear out over time. Here we see the bones of the thoracic cage, the sternum on the anterior along the midline has three major regions. The manubrium literally translates as the handle. The body and then the xiphoid process is the pointed tip. Xiphoid comes from the word for a small pointed sword and the entire sternum looks a little bit like a sword if you hold the manubrium or handle and then the xiphoid is the tip of the sword. On the manubrium here we see a curved surface on the superior known as the jugular notch and where the manubrium meets the body is the sternal angle. There are 24 ribs which articulate with the 12 thoracic vertebrae, 12 on the left and 12 on the right. The ribs start with the first thoracic vertebrae. The first through seventh are known as true ribs. The true ribs extend from T1 through T7 and have costal cartilage connecting over to the sternum. Here we can see the costal cartilage of the true ribs and then false ribs are the inferior ribs from 8 to 12. Notice that 8, 9 and 10 have costal cartilage that is shared with the costal cartilage of 7 ribs 11 and 12 have no costal cartilage and so ribs 11 and 12 are known as the floating ribs. Here we have an inferior view of a left rib. We can see the head of the rib. This is the region that articulates with the vertebral body of the thoracic vertebrae, the costal facets on the vertebral bodies articulate with the head of the rib. Then the tubercle of the rib is a small rough projection of bone that articulates with the costal facets on the transverse processes of thoracic vertebrae. The neck is the region between the tubercle and the head. Then there is a costal groove on the inferior surface. This is a groove that contains nerves and blood vessels. The intercostal nerves and blood vessels are traveling in this groove. The angle of the rib is the point of greatest curvature. Here we can see an illustration of the articulation between a rib and a thoracic vertebrae where the head of the rib articulates with the costal facets the superior and inferior costal facets on the body of a thoracic vertebrae surround the head of a rib and then on the transverse process of a thoracic vertebrae there is another costal facet and this is the facet that articulates with the tubercle of the rib. Here we can see the costal facet on the transverse process articulating with the tubercle of the rib.