There are a total of 7 cervical vertebrae, and with the hyoid bone, they form the skeleton of the neck extending from the base of the skull superiorly, inferiorly till the 1st thoracic vertebra. The spinal nerves emerge above the corresponding vertebrae – for example, C3 spinal nerve comes off above the C3 vertebra.
The typical cervical vertebrae are C3, C4, C5 and C6.
The atypical cervical vertebrae are C1 – Atlas, C2 – Axis and C7 – vertebra prominens.
It should be noted that all vertebrae except C1 and C2 consist of two broad portions:
- Body: Large, central mass of bone.
- Vertebral Arch: Visible in every diagram, consists of a pedicle which connects the body to the articular processes, and a lamina that connects the articular processes to the spinous process. Don’t worry, this will be explained below.
Features of a Typical Cervical Vertebra:
- Small, Wide Body – Looking very carefully at the shape of the body, you can notice that some edges of the body are raised. Typically, the superior surface of the typical cervical vertebrae are raised or elevated greatly at the posterior rim, marginally at the lateral rim, and depressed at the anterior rim. This phenomenon results in the superior surface being called an uncus. What does this resemble? Think of a chair. Conveniently, the inferior surface of the cervical vertebrae have a “bevelled” surface, or a surface that complements or fits into the superior surface of the vertebra below it. This allows a special type of joint called a uncovertebral joint, that really just resembles chairs stacking one on top another. Just look at this diagram, you’ll see what I mean.
- Large, triangular vertebral foramen – Nerves supplying the arm come from the cervical enlargement of the spinal cord. Since the spinal cord is so large here, the vertebral foramen must also be large to accommodate it.
- Tranverse Process with Foramen Transversarium – The foramen transversarium, labeled as a large hole or passageway through the transverse process of the vertebra, is the most characteristic feature of the cervical vertebrae. Its function is to allow the passage of the vertebral artery, accompanying vertebral veins and branch of inferior cervical ganglia, specifically though the foramina transversaria of C6 to C1. Hence, the name vertebral artery is given to this very important artery, as it runs within the vertebra itself. It should be noted however, that the C7 foramen transversarium is very small, and may be absent occasionally, and serves only to carry small accessory veins.
- Transverse Process with Anterior and Posterior Tubercle – Labelled in most diagrams on this post, the anterior and posterior tubercle arise due to the embryology of the cervical vertebra. The transverse process in fact, is derived from 2 parts embryologically: a posterior transverse element (part of the neural arch), and an anterior costal element, labelled in the diagram below. The costal element is unique, as within the thoracic vertebrae, it projects anteriorly to form the ribs. In the cervical vertebrae, you can also imagine the costal element in an attempt to protrude anteriorly to form ribs, but is not able to complete its attempt. Hence there is an anteriorly projecting anterior tubercle, and a posteriorly projecting posterior tubercle, both which serve for attachment of muscles. The portion connecting the anterior tubercle and posterior tubercle to the pedicle of the vertebra is the anterior and posterior root. Both anterior and posterior tubercle are also connected to each other by a costotransverse bar, labelled in the diagram above. The costotransverse bar forms a groove for the passage of the anterior rami of the cervical spinal nerve as it exits the vertebra. You can therefore think of the transverse process as 2 roots extending out from the lamina, connected to each other at the tips by the costotransverse bar, forming an open circle through which the vertebral artery and accompanying veins pass. It should be noted that the anterior tubercle of C6 is especially large and is called the carotid tubercle because the common carotid artery can be palpated against this tubercle, and it separates the common carotid from the vertebral artery.
- Spinous Processes That are Short and Bifid – Visible in all the diagrams as a large, projecting portion of the vertebrae, the spinous processes are formed by the fusion of the two laminae along the midline. Typically, the spinous process extends inferiorly to protect the cervical vertebra below it. However, in the vertebrae C3-C5, the spinous process is very short. It should be noted however, that the spinous processes become larger from C3 – C7, and the spinous process of C6 is actually classified as a long spinous process (it is thus an exception to the generalization that the spinous process is short for the typical cervical vertebrae. The spinous process of C7 is even longer, and is usually the longest in the body – hence called the vertebra prominens, since it is so prominent. The spinous process is also classified as bifid, meaning it has two inferiorly projecting endings. All the typical cervical vertebrae (C3-C6) are bifid. C7 is again, an exception, and is in fact, not bifid.
- Articular Processes – All vertebrae possess a superior and an inferior articular processes, that articulate to form a type of plane synovial joint called a zygapophyseal (facet) joint, that keeps the vertebrae together. It is very important to understand that the type of movement allowed by the vertebra depends on the shape of these articular processes, and the resulting zygapophyseal joint. For example, the most allowed movement in the cervical vertebrae is flexion and extension. Thus, the articular processes must face in a sagittal plane (i.e. must face anteriorly and posteriorly with respect to each other). Refer to the diagram of the facet joint above. As you can see, it will be impossible to carry out a different type of motion, such as rotation, as the direction the facets face do not allow that motion. In cervical vertebrae, the superior articular process faces posterosuperiorly (backwards and slightly upwards) to articulate with the anteroinferiorly facing inferior articular process of the different vertebra above it. Both superior and inferior articular process of the same vertebra are fused to the junction between the pedicle and lamina along an articular pillar, called the pars interarticularis.
So what makes C7 so different?
C7 is atypical due to the following features:
- Small/absent foramen transversarium, that carries accessory veins rather than the vertebral artery.
- Very long spinous process that is not bifid.
- Anterior tubercle and root of C7 is especially small, and provides attachment for the suprapleural membrane.
The cervical vertebrae are also used as important landmarks along the neck:
- At the level of C3: mandible and hyoid bone
- At the level of C4: common carotid artery bifurcates, superior border of thyroid cartilage
- At the level of C4-C5: Thyroid cartilage
- At the level of C6-C7: Cricoid cartilage
Movements of the Cervical Vertebra
The movement of the cervical vertebra has a specific range and type.
The Range is determined by the intervertebral disc and the Type is determined by the zygapophyseal joint between the cervical vertebrae.
The cervical vertebrae all have an intervertebral disc between them. This intervertebral disc is thin in comparison to other IV discs, however when compared to the body, which is exceptionally thin since cervical vertebrae are not weight bearing bones, the IV disc is very thick. This relative thickness of the IV disc determines the range of movement, and since the relative thickness is high, the cervical vertebrae are high.
Second, we must consider the shape of the articular facets of the zygapophyseal joints. Because the joints face anteriorly and posteriorly, as explained above and in the diagram above, it means the best supported movement is extension and flexion, and the least supported movement is rotation.
If you guys are confused by the zygapophyseal joints, check this youtube video:
And here’s a nice animation for you guys to experiment with on cervical vertebrae as well!