The cervical vertebral column is the one most capable of movement. The first cervical vertebrae (atlas) and the second cervical vertebrae (axis) deviate significantly from the basic form of the cervical vertebrae. For instance, the atlas does not have the body of the vertebrae or spine of the vertebrae. Instead of that, it has two arches with joint surfaces for the axis and the occipital bone (os occipitale).
The second cervical vertebra has a tooth-like process (dens axis), which connects the front surface of the joint of the atlas and axis. The cervical vertebrae 3-6 are very similar to one another.
The body of the vertebrae (Corpus vertebrae) continues in the rear in the vertebral arch (arcus vertebrae). It divides up into a front section (pediculus arcus vertebrae) and a rear section (lamina arcus vertebrae). An articular process directed upwards and downwards (processus articulares superiores et inferiores) at the transition of these two parts vaults upward and downward.
The vertebral arch ends in a spine of the vertebrae (processus spinosus), which is divided into two at the third to sixth cervical vertebra. There is the vertebral foramen (foramen vertebrale) between the vertebral arch and the bodies of the vertebrae. It is relatively large at the cervical vertebrae. There is a transverse process on each side (processus transversus) that forms the jointed connection to the ribs.
The seventh cervical vertebra differs from those mentioned above, because it has a particularly long spine of the vertebrae that makes the skin protrude significantly (vertebra prominens). It can also be easily seen and felt.
The cervical vertebral column can be inclined approximately 90 degrees backwards, 40 degrees forwards and 35 degrees to the side. The head is rotated primarily through the atlanto-occipital joint.
We differentiate between and upper and a lower head joint. The first cervical vertebra (atlas) and the second cervical vertebra (axis) are connected to them. In contrast to the other vertebrae, they do not bear a great load. However, they ensure that the head has a wide radius of movement in relation to the vertebral column (columna vertebralis).
The first cervical vertebra and the occipital bone (os occipitale) are connected to the upper head joint (articulatio atlantooccipitalis). These two correspond to the ellipsoid joint in their form. Their joint surfaces are the fascies articulares superiores, meaning the swelling of the first cervical vertebra (massa lateralis) and the two-part joint surfaces of the occipital bone (condylii occipitales). They do not fit one another exactly and allow lateral movement (up to 20 degrees) and nodding movements (up to 30 degree). The cervical vertebral column and parts of the thoracic spine are also moved with larger head movements.
The lower head joint (articulatio atlantoaxialis) is a rotary joint. It consists of the lateral (articulatio atlantoaxialis lateralis), and the middle joint (articulatio atlantoaxialis mediana) between the first cervical vertebra (atlas) and the second cervical vertebra (axis). The joint surfaces of the lateral joints are the inner swellings of the first cervical vertebra (facies articulares inferiores atlantis) and the cartilaginous spines of a vertebra of the second cervical vertebra that are directed upwards (processus articulares superiores axis). In this process, the second cervical vertebra pushes a bony process (dens axis) into a recess of the first cervical vertebras. The joint surfaces of the lateral joints are the facies articularis anterior dentis (at the dental process of the second cervical vertebra) and a concave joint surface of the first cervical vertebra (fovea dentis) on the rear surface of the front first cervical vertebra.
It is possible to stretch approximately 26 degrees in both sides from the lower head joint. Beyond this, this allows light nodding and stretching movements because the joint surfaces do not fit exactly.
Both of the head joints are secured by ligaments to prevent potentially uncontrolled rotary, stretching or bending movements that could be dangerous to the spinal cord. Among them are tracts of connective tissue over large surfaces such as the membranae atlantooccipitalesi anterior (between the front first cervical vertebra and the occipital bone (os occipitale)) and membranae atlantooccipitalesi posterior (between the first cervical vertebra and the head).
The odontoid ligaments (ligamenta alaria) connect the head
with the first cervical vertebra and keep the head from being
extended. The ligamentum apicis dentis is a ligament between the
tip of the tooth of the second cervical vertebra and the front
hole of the large occipital foramen. An important ligament of
connective tissue is also the ligamentum transversum atlantis.
It stretches between the right and left lateral swelling (massa
lateralis) of the first cervical vertebra within the lower head
joint. There are also other ligaments that prevent excessive
rotation, tipping or stretching.
The interaction of the atlas and axis.
The first cervical vertebra differs very basically from the others, because it does not have a body (corpus vertebrae) or the spine of the vertebrae (processus spinosus). In compensation, it has a front arch (arcus anterior) and a rear arch (arcus posterior). They combine to be a lateral swelling (massa lateralis) that bears the joint surface for the articular process of the occiputs (condylus occipitalis).
The vertebral foramen (foramen vertebrale) is in-between and is large at this vertebra. The transverse processes (processus transversi), which are interrupted by holes, the foramina transversaria, emanate from the massae. Finally, there is a little protuberance on the front and rear arch (tuberculum anterius et posterius).
Click on the image for a 3D view of the Atlas.
The second cervical vertebra, also called the "epistropheus",
differs from the third to sixth cervical vertebrae
through the cone (tooth), which projects from its
vertebral body (dens axis).
This "tooth" ends with a rounded-off tip (apex dentis). Instead of articular processes (processus articulares superiores et inferiores), there are joint surfaces (facies articularis anterior et posterior) on its front and also on its rear surface. The rear one is somewhat smaller. The position of the dens axis to the body of the second cervical vertebra depends upon the curvature of the cervical vertebral column. It may be directed somewhat towards the back.
The transverse processes (processus transversi) are not formed very prominently. They contain one hole each for the vertebral artery, the foramen transversarium. Even if the lateral joint surfaces seem to be smooth, they still have small deposits of cartilage that are important for the joints between the first and the second cervical vertebra.
The spine of the axis (processus spinosus) has a powerful construction. Sometimes it has a double tip. It is formed out of the two vertebral arches coming together (arcus vertebrae). They jointly surround the vertebral foramen (foramen vertebrale) with the body of the vertebrae (corpus vertebrae).
Click on the image for a 3D view of the Axis.
