Video: Vertebral column
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Want to know the main difference between us and Lobby? Well, apart from the fact that he's green, made out of jelly, and pretty much lacks any resemblance to the human body – he doesn't have a vert... Read more
Want to know the main difference between us and Lobby? Well, apart from the fact that he's green, made out of jelly, and pretty much lacks any resemblance to the human body – he doesn't have a vertebral column, which is one of the reasons why he can morph, bend, and jiggle around the place. The vertebrae which make up the spine provide structural support allowing us to maintain an upright posture and even though they won't enable us to be a jelly monster, they do allow some flexible motion. Find out more about the features of the vertebral column in today's tutorial.
Before we kick off, here's a quick overview of what we'll look at today. We'll begin by looking at the vertebral column as a whole and discover the five regions it's divided into – the cervical, thoracic, lumbar, sacral, and coccygeal regions. Next up, we'll look at the general features of the vertebrae focusing on the main components and bony landmarks of a typical vertebra. We'll then explore the curvatures of the spine and the movements and function of the vertebral column as a whole. To wrap up, we'll then take a look at some clinical scenarios related to this part of the body.
So first up are the regions of the vertebral column. We'll start superiorly and work our way inferiorly.
As we already discovered, the vertebral column is composed of 33 to 35 vertebrae – 24 of which are interconnected by cartilaginous intervertebral discs. The vertebral column extends from the base of the skull to the tip of the coccyx and as we already saw is divided into five regions – the cervical, thoracic, lumbar, sacral, and coccygeal regions. The cervical to lumbar vertebrae are interconnected by intervertebral discs whereas the sacral and coccygeal vertebrae are fused. We'll take a closer look at each of these regions now.
There are seven cervical vertebrae, all of which are found in the neck region. Superiorly, the cervical spine articulates with the occipital bone of the skull to form the atlantooccipital joint and inferiorly with the first thoracic vertebra.
The longest segment of the vertebral column is the thoracic spine made up of twelve vertebrae. Superiorly, the thoracic spine articulates with the seventh cervical vertebra, and inferiorly, with the first lumbar vertebra. Each thoracic vertebra also articulates with the ribs of the thoracic wall.
The next section of the vertebral column is made up of the five lumbar vertebrae. The lumbar vertebrae are located inferior to the rib cage and superior to the pelvis and the sacrum. These vertebrae are the largest segments of the vertebral column as they are mainly responsible for bearing the weight of the upper body. Superiorly, the lumbar vertebrae articulate with the twelfth thoracic vertebra, and inferiorly, with the first sacral vertebra to form the lumbosacral joint.
The sacrum is an irregularly-shaped bone made up of a group of five fused vertebrae in the area of what is commonly known as the base of the spine. The sacrum is important because it forms a link between the spine and the iliac bones and also has an important part to play in hip stability. The sacrum articulates superiorly with the fifth lumbar vertebra forming the lumbosacral joint and inferiorly with the base of the coccyx to form the sacrococcygeal joint. It also articulates with the iliac bones of the pelvis to form the sacroiliac joints.
The most inferior part of the vertebral column is composed of three to five coccygeal vertebrae fused together to form the coccyx which is also known as the tailbone. The coccyx articulates with the apex of the sacrum superiorly forming the sacrococcygeal joint.
Now that we have a general understanding of the structure and regions of the vertebral column, let's take a closer look at the features of a typical vertebra.
No two vertebrae are identical. They vary in size and characteristics especially from one region to the next. However, most vertebrae have a basic structure and are therefore known as typical vertebrae. A typical vertebra consists of a vertebral body, vertebral arch, and seven processes. As the vertebrae of the sacrum and coccyx are fused, the general structure of a typical vertebra does not apply to them; however, this typical structure can be identified within the vertebrae of the cervical, thoracic, and lumbar regions.
Here we are looking at an isolated vertebra of the thoracic region; however, we're not going to focus on a specific vertebra but more just the features of a typical vertebra in general. Let's begin with the vertebral body.
The vertebral body is the weightbearing structure of the vertebral column. It therefore needs to be large and solid. The vertebral body faces anteriorly so if you look at the spinal column from an anterior view, the vertebral bodies are mostly what you'll see. The size of each vertebral body increases as the vertebral column descends, therefore, the vertebral body of a cervical vertebra will be much smaller than the vertebral body of a lumbar vertebra. Separating each vertebral body from adjacent vertebrae are the intervertebral discs. Unique to the vertebral bodies of thoracic vertebrae are the costal facets.
The thoracic vertebrae articulate with ribs 1 to 12 at the superior and inferior costal facets of the vertebral body and the costal facet of the transverse process. Typical thoracic vertebrae present with a total of six costal facets per vertebrae – two on the transverse processes and four demi-facets on each vertebral body.
The next feature of a typical vertebra is the vertebral arch. The vertebral arch is located posterior to the vertebral body and forms the posterolateral aspect of each vertebra. Each vertebral arch consists of two pedicles and laminae. The pedicles, laminae, and body of each vertebra collectively form a cavity known as the vertebral foramen. We'll explore this structure in more detail later on but first let's take a closer look at the bony landmarks of the vertebral arch.
The narrower ventral portion of the vertebral arch is known as the pedicles. The pedicles arise as short, rounded dorsal projections from the superior aspect of the vertebral body. The pedicles contain superior and inferior vertebral notches which form intervertebral foramina when articulating with adjacent vertebrae. The intervertebral foramina facilitate the passage of spinal nerves from the spinal cord.
The broader dorsal portion of the vertebral arch is known as the lamina. The laminae are broad bony plates that project posteromedially from the posterior ends of the pedicles. They form the posterolateral parts of the vertebral arch and the posterolateral walls of the vertebral foramen. The laminae construct the roof of the spinal canal and connects the spinous process to the transverse processes which we'll have a look at next.
Projecting from the vertebral arch are seven vertebral processes which include one spinous process, two transverse processes, and four articular processes. The vertebral processes serve as attachment points for ligaments and back muscles. They also take part in joint formation. The spinous process is a bony projection which arises from the posterior aspect of the junction of the laminae. Spinous processes vary in size, shape, and direction; however, they usually lie in the median plane and project posteriorly. They function as an attachment point for muscles and ligaments of the back.
The structure and length of each spinous process can differ according to vertebral regions. The spinous processes of the cervical spinal vertebrae are often shorter and smaller than the spinous processes of the thoracic and lumbar vertebrae and are often bifid. Although cervical vertebrae usually have shorter spinous processes, the most prominent spinous process can be seen at the seventh cervical vertebra. If you tuck your chin in and feel the posterior aspect of the base of the neck, you might feel a small bony prominence. This is your C7 spinous process.
Projecting laterally from the vertebral arch on either side at the pediculolaminar junctions are the two transverse processes. The transverse processes serve as an important attachment point for muscles and ligaments of the back and neck which facilitate rotation and lateral flexion. There is considerable regional variation in the length and structure of the transverse processes. For example, in the cervical region, the transverse processes are often shorter, bear anterior and posterior tubercles and a transverse foramen. They are usually located anterior to the articular processes, lateral to the pedicles, and in between the intervertebral foramina.
In the thoracic region, they are located posterior to the pedicles and the width of the transverse processes decreases as the thoracic vertebrae descend. The transverse processes of the upper three lumbar vertebrae are typically broad but have been identified to be narrower in the lower two lumbar vertebrae. Within the lumbar region, the transverse processes are located anterior to the articular processes but posterior to the intervertebral foramina.
Moving on to the final group of vertebral processes, we meet the four articular processes. The articular processes are projections of vertebrae which function to articulate with vertebrae above and below. The articular processes are divided into two superior and two inferior articular processes. The superior articular processes, as their name suggests, are located on the superior aspect of the vertebral arch. They are the two upward projecting processes at the junction of the laminae and pedicles. Located on each superior articular process is a smooth, flattened surface known as the superior articular facet.
The superior articular facets connect with the inferior articular facets of the vertebra above forming a facet or zygapophyseal joint. The inferior articular processes are two inferior projecting processes located on the inferior aspect of each vertebral arch. They possess inferior articular facets which articulate with the superior articular facets of the vertebra below forming the aforementioned zygapophyseal joints.
The final feature of a typical vertebra is the central opening which is known as the vertebral foramen. The boundaries of the vertebral foramen are formed by the posterior aspect of the body of the vertebrae anteriorly and by the vertebral arch posterolaterally. A continuous series of vertebral foramina extending from the first cervical vertebra to the fifth lumbar vertebra collectively forms the vertebral canal which houses the spinal cord. The vertebral foramina gradually decrease in size as the vertebral column descends, therefore, the vertebral foramina of the cervical region are larger than the vertebral foramina of the lumbar region.
The shape of the vertebral foramen may also differ according to vertebral regions. The cervical and lumbar vertebrae have triangular-shaped vertebral foramina whereas the thoracic vertebrae have more round or oval-shaped vertebral foramina.
Now that we've explored the structure and typical features of the vertebrae, let's take a look at the curvatures of the spine.
From this anterior view, the vertebral column looks pretty straight; however, if we change our view to a lateral perspective, we can see that there are a few twists and turns along the way. The four curvatures of the spine function to provide flexible support for the body and are formed by the cervical, thoracic, lumbar, and sacral regions of the vertebral column. The spinal curvatures can be divided into two primary and two secondary curvatures.
The thoracic and sacral curvatures are termed the primary curvatures as they appear during embryonic development. These curvatures are concave anteriorly or convex dorsally as a result of the flexed fetal position and are referred to as kyphosis. Thoracic kyphosis extends between the second and the eleventh and twelfth thoracic vertebrae. This curve is caused by a result of differences in height between the anterior and posterior components of the vertebrae. Thoracic kyphosis has a normal range of approximately 20 to 50 degrees.
Anterior concavity of the sacral or pelvic region is known as sacral kyphosis or pelvic curve. The pelvic curve involves the sacral and coccygeal vertebrae and extends from the lumbosacral junction to the apex of the coccyx. The degree of sacral curvature of the female vertebra is usually reduced resulting in decreased protrusion of the coccyx into the pelvic outlet maintaining the patency of the birth canal.
The secondary curvatures appear during the late fetal period as a result of extension from the flexed fetal position and did not become obvious until infancy. The secondary curvatures consist of the cervical and lumbar lordosis. Lordosis refers to the posterior concavity of the spine which is visible from its lateral view. Secondary curvatures are not permanent curvatures and are maintained during child and adulthood due to the differences in thickness between the anterior and posterior parts of the intervertebral discs.
As we begin to age, our secondary curvatures may disappear as the vertebral column takes on more of a C-shaped curve. This is a result of intervertebral disc degeneration as part of the natural progression of aging. Cervical lordosis appears late in fetal life and becomes more pronounced between 6 to 12 weeks after birth as the infant begins to hold its head up. The posterior concavity of the cervical curvature is relatively shallow when compared with the degree in curvature of lumbar lordosis. It begins in the dens axis and extends to the level of the second thoracic vertebra.
Lumbar lordosis appears when a child begins to sit up at around six months. It becomes increasingly marked as a child begins to stand and walk and is fully developed at around two years of age once the adult pattern of walking has been established. The lumbar curvature begins at T12 and terminates at the lumbosacral joint. It functions to keep the trunk erect when standing. Changes in pelvic tilt are accompanied with changes in lumbar curvature in an attempt to keep the trunk upright. Wearing high heels moves the pelvis forward thus increasing the degree of lumbar lordosis. The same happens during pregnancy as the center of gravity changes resulting in increased lumbar lordosis in an effort to stabilize the trunk.
Now that we have an understanding of the curvature of the spine, let's explore the functions and movements of the vertebral column as a whole.
The range of movement of the vertebral column varies according to the vertebral region and the individual. The mobility of the vertebral column results primarily from the compressibility and elasticity of the intervertebral discs. The vertebral column can produce movements of flexion, extension, lateral flexion, and rotation. These movements are mainly facilitated by the muscles of the back; however, they are also assisted by gravity and the action of the anterolateral abdominal muscles.
The normal curvatures of the vertebral column also contribute to its flexibility as they impart resilience to axial compressive forces which are absorbed by the giving way and recovery of the various curves. The cervical and lumbar regions of the vertebral column allow for the greatest degree of movement. Structures which stabilize and resist movement of the vertebral column include the thickness, elasticity, and compressibility of the intervertebral discs; the shape and orientation of the facet joints; the tension of the articular capsules of the zygapophyseal joints; and finally, the resistance of the back muscles and ligaments. As well as providing flexible structure to the trunk, the vertebral column also functions to protect and contain the spinal cord which traverses the length of the vertebral column within the vertebral canal.
Phew! That's a lot of information on the vertebral column. Let's work on consolidating that knowledge by applying it to a clinical scenario.
As we have seen, the vertebral column is not a straight structure but possesses four curves which function to facilitate flexible support and movement. Abnormal curvatures of the spine may also occur and often result from developmental anomalies or as a result of pathological processes. Hyperkyphosis, colloquially known as humpback or hunchback, is characterized by an abnormal increase in the thoracic curvature resulting in the vertebral column to curve posteriorly. This abnormality can result from erosion of the anterior part of one or more vertebrae as a result of osteoporosis, muscular weakening. and aging. A kyphosis angle greater than 50 degrees is indicative of hyperkyphosis.
Hyperlordosis, colloquially known as hollowback or swayback, is characterized by an anterior rotation of the pelvis whereby the upper sacrum tilts anteroinferiorly at the hip joints. This movement produces an abnormal increase in lumbar curvature resulting in the vertebral column to curve more anteriorly. Hyperlordosis is often associated with weakened trunk musculature especially the anterolateral abdominal muscles and is frequently seen to occur during pregnancy or as a result of obesity. A lordosis angle greater than 40 degrees is indicative of hyperlordosis.
Scoliosis is characterized by an abnormal lateral curvature that is accompanied by rotation of the vertebrae. The spinous processes turn toward the cavity of the abnormal curvature and when the individual bends over, the ribs rotate posteriorly on the side of increased convexity. Asymmetrical weakness of the intrinsic back muscle, failure of half of vertebra to develop, and a difference in the length of the lower limbs are causes of scoliosis.
Treatments for abnormal back curvature are dependent on the original cause. They are often treated through physical therapy, and in severe cases, surgical fusion and bracing. In cases where hyperlordosis is a result of obesity, weight loss and exercise are recommended.
We've made it to the end of this tutorial. But before you rush off, let's take some time to go over what we learnt today.
We began today's tutorial with a general overview of the regions of the vertebral column. Here we explored the general structure of the cervical, thoracic, lumbar, sacral, and coccygeal regions of the spine. Moving on, we explored the structural features of a typical vertebra which include the vertebral body, vertebral arch, and the vertebral foramen. We also identified components of the vertebral arch which include the pedicle, laminae, and seven processes.
The seven processes of the vertebral arch include the spinous process, the two transverse processes, the two superior articular processes, and the two inferior articular processes. We then examined the vertebral column as a whole and appreciated its curvatures. We explored the primary and secondary curvatures of the vertebral column. The primary curvatures encompass thoracic and sacral kyphosis which appear during embryonic development. The secondary curvatures include the cervical and lumbar lordosis which begin forming during the later stages of fetal development.
Next, we explore the movements and functions of the vertebral column. Movements of the vertebral column include flexion, extension, lateral flexion, and rotation. These movements are facilitated by the muscles and ligaments of the back and the anterolateral abdominal wall muscles. Besides facilitating movement, the vertebral column also functions to house and protect the spinal cord.
To finish today's tutorial, we examined the effects of abnormal curvatures of the spine. We explored the causes, diagnosis, and treatment of hyperkyphosis, hyperlordosis, and scoliosis.
And that's all for today. I hope you enjoyed learning about the vertebral column, and happy studying!