The Cervical Spine

HWS und KopfgelenkThe cervical spine is the most flexible, but also the weakest part of the entire spinal column. It is divided in

   the “classic” cervical spine with five parts (C3-C7)


   the head joint area consisting of the Atlas (C1),
     the Axis (C2) and the moving segment C2/3

 

 

The head joint area

The head joint area is composed of the upper and lower head joint. The upper joint (Articulatio

Atlas
Taken from: Huch/Bauer: Mensch Körper Krankheit, 4.Aufl., 2003 Urban + Fischer Verlag, München, Jena

atlantooccipipitalis) is made up of the first cervical vertebra, the atlas (C1) and the articular surfaces of the occipital bone. The atlas is the only vertebra without a body. On the other hand this vertebra shows so-called outgrowths (Massa lateralis) on the right and left side which can be seen in the picture on the right with the blue kidney-shaped areas.
These outgrowths are connected via the front and rear atlas arch. The top of the outgrowths are formed by two sockets that are brought into contact with the so-called “condyles” of the occipital bone. The articular surfaces do not match exactly, which gives us the possibility to perform nodding (max. 30 degrees) and lateral declines (less than 20 degrees). You can say that the atlas “carries” the head, as the giant Atlas from Greek mythology carried the firmament on his shoulders. He also gave the vertebra its name. The atlas has to support the weight of the head with up to 7 kilograms.

Axis und das Querband des Dens
Taken from: Huch/Bauer: Mensch Körper Krankheit, 4.Aufl., 2003 Urban + Fischer Verlag, München, Jena

DThe axis is the second vertebra, also called C2, and it forms the lower head joint (Articulatio atlantoaxialis). The Axis is specialised on rotational movements. Thereby the round sockets at the bottom of the atlas get into contact with the corresponding articular surfaces of the axis. The axis already has a vertebral body and an arch, as well as strong transverse and spinal processes. The most outstanding characteristic of the axis is its dens axis. The dens is a strong outgrowth to the top and reaches up to the atlas. At its front side it is covered with cartilage and shows a flat socket on the inner side the atlas.. The rear side, also covered with cartilage, slides on a stable transverse ligament (Ligamenta transversa) which is tightened between the two outgrowths of the atlas (see above picture). That way a hollow space (similar to a fissure) is created between the front atlas arch and the transverse ligament. In this space the dens can move and perform rotations of 15° to 25° to the left or right. Minor stretching and nodding movements are also possible because once again the lateral angular surfaces do not match exactly.
Die Bänder des KopfgelenksThe
head joint is very flexible since it is rather “loose”. Yet to prevent uncontrolled stretching, bending and turning movements from injuring the spinal cord, several ligaments inhibit the movement types in the head joint. The Membrana atlantooccipitalis anterior reaches from between the front atlas arch to the occipital bone. This ligament prevents excessive stretching in the upper head joint. There are three other important ligaments which can be seen in the adjacent illustration. These run in a V-shape from the dens to the front and lateral margin of the foramen occipitale magnum. The lateral ligaments are called Ligamenta alaria, the ligament in the middle is called Ligamenta cruciforme. These ligaments prohibit inordinate turning and tilting movements in the lower head joint. A “complete” image of the head joint as a summary can be found here.

 

The classical Cervical Spine

The classical cervical spine consists of five vertebrae C3 to C7

Bild eines Halswirbels

Halswirbel
taken from: Huch/Bauer: Mensch Körper Krankheit, 4.Aufl., 2003 Urban + Fischer Verlag, München, Jena

Halswirbelsäule The vertebrae do largely have the typical basic vertebral form, but they can be recognized by the Foramina transversaria as cervical vertebrae (this is a kind of canal for arteries). The cervical vertebrae are smaller compared to the ones of the remaining spinal column, increasing their size from cranial (top) to caudal (bottom). They are also diagonally wider than from the front to the rear.
The upper front surface of the vertebra is formed like a scoop. The margins of this area are accumulated, which is called Uncus corporis, the bottom however is bevelled and crenated. From time to time there are small outgrowths of bones coming from the Uncus corporis which can exercise pressure on the respective spinal nerves. The cervical holes are rather large because they absorb the cervical intumescence of the spinal cord (Intumenscentia cervicalis). With its upper process, also called Facies articularis superior, each cervical vertebra is in contact with the lower angular process of the vertebra above. That way the vertebral canal of the cervical spine is formed, which is as well known as Foramina intervertebralia.

The 7th cervical vertebra (Vertebra prominens) stands a bit apart from the other cervical vertebrae. Its very long spinal process ends in a distinct hunch. This hunch can be palpated quite easily at the lower end of the neck furrow. The 7th cervical vertebra sometimes lacks the Foramen transversarium on one or both sides.

The cervical spine accommodates as well part of the spinal cord, namely 8 spinal cord segments (cervical segments) that supply especially the respiratory musculature and the upper extremities.. Arterienverlauf in der HWS und im KopfBut not only nerve cords run through the cervical spine, there are also arteries using it as a “canal”. The most important arteries here are the two Arteria vertebralis. Both arteries emanate from the Arteria subclavia (Arteria is the Latin word for artery) and pass on the left and right of the cervical spine through the Foramina transversi (plural form of Foramina transversaria) of the 6th to the 2nd cervical vertebrae. After the passage through the 2nd vertebra each artery makes a dorsal bend (to the rear) and runs on the rear atlas arch, this is the atlas loop of the artery. Then the arteries enter the cranial cavity and then continue forward again (cranial). Both Arteria vertebralis merge into the Arteria basilaris.
These arteries supply the cerebellum, parts of the mesencephalon and of the brain stem, furthermore hearing and equilibrium organs and rear components of the cerebrum as well as cervical spinal nerves and ganglia (nerve roots). It has to be noticed that the artery has very little expansibility.

I hope I was able to explain you a bit the sophisticated and complicated structure of the cervical spine. In my opinion, these explanations are important in order to understand the consequences that injuries of the cervical spine can implicate. Unfortunately injuries of the cervical spine do often occur in our engineered world, just think of the whiplash injury.

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