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.
On the anterior arch, there’s a tubercle for the transverse ligament. The transverse
ligament extends from one lateral mass to the other lateral mass on the atlas,
passing between the spinal cord and the dens, which is a part of the C2 vertebra.
Speaking of which, the C2 vertebra is also called the axis, because it
has a blunt tooth-like dens or odontoid process. The dens projects superiorly,
and articulates with the posterior surface of the anterior arch of the atlas,
and it’s held in place by the transverse ligament. Next, C2 also has two large, flat
bearing surfaces called the superior articular facets on which the atlas rotates. It also has
inferior articular processes, and transverse processes similar to the other cervical vertebra.
Now, C2 also has a large bifid spinous process that can be felt deep in the nuchal groove,
which is the superficial vertical groove at the back of the neck.
Now, the atlas and the axis join together and form the atlanto-axial joint which is a
complex joint made up of three synovial joints: one median joint and two lateral joints. The
lateral joints consist of the lateral masses of atlas and axis, while the median joint is between
the posterior surface of the anterior arch of atlas and the front of the odontoid process.
The primary movement in this joint is rotation,
or moving the head side to side known as the ‘no’ movement.
Finally, C7 is also called the vertebra prominens, because it has a long spinous process.
You can actually feel it if superficially palpate as you
run your finger and press along the midline of the back of your neck!
Let’s take a quick break and try to identify the features of a typical vertebra,
as well as identify the three atypical vertebrae based on their features.
Now, let’s see what the hyoid bone is all about. This one is a U-shaped,
mobile bone located in the anterior part of the neck at the level of C3 vertebra.
Specifically, it sits in the angle between the mandible and the thyroid cartilage.
Interestingly enough, the hyoid doesn’t articulate with any other bone. Instead, it’s suspended from
muscles connecting it to multiple structures including the mandible, styloid process,
and thyroid cartilage. The hyoid bone is connected to the styloid processes of the temporal bones
by the stylohyoid ligaments and is firmly bound to the thyroid cartilage. Functionally,
it serves as an attachment for anterior neck muscles and a prop to keep the airway open.
Now, the hyoid bone itself consists of a body and greater and lesser horns. The body of the hyoid is
located in the middle, it faces anteriorly and has an anterior convex surface which projects
anterosuperiorly and a posterior concave surface which projects posteroinferiorly. So far so good.
Now, each end of the body is united with a greater horn that projects posterosuperiorly and laterally
from the body. And near the junction between the body and the greater horn on either side, there’s
a lesser horn, which projects superoposteriorly toward the styloid process. The lesser horns
are connected with the body by fibrous tissue and sometimes to the greater horn by a synovial joint.
All right, as a quick recap. The skeleton of the neck is formed by the cervical region of the
vertebral column and the hyoid bone. The cervical column has seven vertebrae which are both typical
and atypical. A typical vertebra has a vertebral body, a vertebral arch and seven processes and
are represented by four of the cervical vertebrae: C3, C4, C5 and C6. An atypical vertebra has some
unique characteristics that help differentiate it from a typical vertebrae and the cervical column
has three of these vertebrae: C1 or atlas, C2 or axis and C7. C1 articulates with the two large
cranial protuberances of the occipital bone to form the atlanto-occipital joint, permitting
flexion and extension. C1 and C2 articulate to form the atlanto-axial joint, permitting rotation,
or moving the head side to side known as the ‘no’ movement. Finally, there is the hyoid bone,
having no bony articulations and serving as an attachment point for many muscles in the neck.