Bones of the neck

Transcript

The neck is the anatomical region between the base of the cranium superiorly and the clavicles inferiorly and it joins the head to the trunk and limbs, serving as a major conduit for structures passing between them.

The skeleton of the neck is formed by the cervical vertebrae, the hyoid bone, and the manubrium of the sternum which are part of the axial skeleton, as well as the clavicles which are part of the appendicular skeleton.

.Alright, so let’s start with the cervical vertebrae, of which there are 7.

These are the smallest vertebrae, and they form the cervical region of the vertebral column, enclosing the cervical spinal cord and meninges.

Cervical vertebrae can be typical or atypical, and when it comes to the cervical column, the typical vertebrae are C3, C4, C5 and C6, while the atypical vertebrae are C1, C2 and C7.

Ok so, all typical vertebrae have a vertebral body, a vertebral arch and seven individual processes.

The vertebral body is situated anteriorly, and it’s small and longer from side to side than anteroposteriorly.

It has a concave superior surface and a convex inferior surface.

These surfaces are the vertebral endplates, which help form the intervertebral joints together with the intervertebral discs and the adjacent vertebra.

On the superior surface, there’s an elevated superolateral margin called the uncus of the body, or the uncinate process.

Next, there’s the vertebral arch, which is located posterior to the vertebral body and is formed by two pedicles and two laminae.

The pedicles are short, thick processes that project posteriorly from the vertebral body to meet the laminae, which are two broad, flat plates of bone, that unite in the midline and complete the vertebral arch.

The vertebral arch and the posterior surface of the vertebral body form the walls of the vertebral foramen through which the spinal cord and its meninges pass.

The vertebral foramen is rather large and, in the cervical region, triangular.

Next up, superior and inferior to the pedicles, there are shallow depressions called vertebral notches.

When the vertebrae articulate, these notches align with those on the neighboring vertebrae and form the openings of the intervertebral foramina through which the spinal nerves emerge from the vertebral column.

Finally, each typical vertebrae has seven processes that arise from the vertebral arch: a spinous process, two transverse processes and four articular processes.

So, the spinous process is located in the middle and projects posteriorly and usually inferiorly, typically overlapping the vertebra below.

Interestingly enough, even though spinous processes are typically unified, meaning they end with a single tip, C3-C6 spinous processes can also be bifid, typically in individuals of European heritage.

Next, there are the two transverse processes, which project laterally and end as two projections called the anterior and posterior tubercle, which serve as muscle attachment points.

The transverse processes of C1 - C6 also have a hole called the foramen transversarium, which serves for the passage of the vertebral arteries and veins.

The foramen transversarium of C7 only houses small accessory veins, and it can be absent.

Finally, the four articular processes, two superior and two inferior, arise from the junctions of the pedicles and laminae, and each has an articular surface or facet.

The superior facets are oriented superoposteriorly and the inferior facets are directed inferoanteriorly.

The superior and inferior articular processes articulate with the corresponding processes of the neighboring vertebrae to form the zygapophysial joints.

These joints determine the types of movement permitted and restricted between the neighboring vertebrae of each region and also they keep the vertebrae aligned, preventing one vertebra from translating, or slipping, anteriorly on the vertebra below.

Now let’s switch gears and look at the atypical vertebrae, called so because they have different characteristics from the other vertebrae.

First, vertebra C1, also called the atlas, is a ring shaped bone that doesn’t have a body or a spinous process.

So, instead of a body, it has paired lateral masses that serve as a body and sustain the weight of the globe-like cranium just like Atlas of Greek mythology, who bore the weight of the world on his shoulders.

The transverse processes of the atlas arise from the lateral masses, so these processes are placed more laterally than those of the inferior vertebrae.

This makes the atlas the widest of the cervical vertebrae.

Now, the lateral masses have two superior, concave, kidney-shaped articular surfaces.

These surfaces articulate with two large cranial protuberances on either side of the foramen magnum on the occipital bone, to form the atlanto-occipital joint.

The movements permitted in this joint are flexion and extension - think about head banging at a rock concert - and a small amount of lateral flexion and rotation, like when you look over your shoulder.

The anterior and posterior arches extend between the lateral masses and form a complete ring.

The anterior arch has an anterior tubercle and a facet for the dens, and the posterior arch has a posterior tubercle and a groove for the vertebral artery.