Cervical vertebrae

Variation among species

In many vertebrate species, cervical vertebrae are variable in number; however, almost all mammals have seven (including those with very short necks relative to body size, such as elephants or whales, and those with very long necks, such as giraffes). The few exceptions include the manatee and the sloths, of which the two-toed sloth has six cervical vertebrae and the three-toed sloth has up to nine cervical vertebrae .

In many species, though not in mammals, the cervical vertebrae bear ribs. In many other groups, such as lizards and saurischian dinosaurs, the cervical ribs are large; in birds they are small and completely fused to the vertebrae. The transverse processes of mammals are homologous to the cervical ribs of other amniotes.

Thoracic vertebrae in all species are defined as those vertebrae which also carry a pair of ribs, and lie caudal to the cervical vertebrae.

In humans, cervical vertebrae are the smallest of the true vertebrae, and can be readily distinguished from those of the thoracic or lumbar regions by the presence of a foramen (hole) in each transverse process, through which passes the vertebral artery.

The remainder of this article focuses upon human anatomy.

General characteristics (C3-C6)

* The body of these four vertebrae is small, and broader from side to side than from front to back.

* The pedicles are directed laterally and backward, and are attached to the body midway between its upper and lower borders, so that the superior vertebral notch is as deep as the inferior, but it is, at the same time, narrower.

* The laminae are narrow, and thinner above than below; the vertebral foramen is large, and of a triangular form.

* The spinous process is short and bifid, the two divisions being often of unequal size.

* The superior and inferior articular processes of cervical vertebrae have fused on either or both sides to form articular pillars, columns of bone which project laterally from the junction of the pedicle and lamina.

* The articular facets are flat and of an oval form:

* The transverse processes are each pierced by the foramen transversarium, which, in the upper six vertebrae, gives passage to the vertebral artery and vein, as well as a plexus of sympathetic nerves. Each process consists of an anterior and a posterior part. These two parts are joined, outside the foramen, by a bar of bone which exhibits a deep sulcus on its upper surface for the passage of the corresponding spinal nerve.

Special cervical vertebrae (C1, C2, and C7)

* C2 or axis: It forms the pivot upon which C1 rotates. The most distinctive characteristic of this bone is the strong odontoid process (dens) which rises perpendicularly from the upper surface of the body. The body is deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and front part of the third vertebra.

* C7 or vertebra prominens: The most distinctive characteristic of this vertebra is the existence of a long and prominent spinous process, hence the name vertebra prominens. In some subjects, the seventh cervical vertebra is associated with an abnormal pair of ribs, known as cervical ribs. These ribs are usually small, but may occasionally compress blood vessels (such as the subclavian artery) or nerves in the brachial plexus, causing ischemic muscle pain, numbness, tingling, and weakness in the upper limb.

Movements of the cervical spine

The movement of shaking or rotating the head left and right happens almost entirely at the joint between the atlas and the axis, the atlanto-axial joint. A small amount of rotation of the vertebral column itself contributes to the movement.

Landmarks

Teeth (when mouth remains closed) correspond to C2.

Mandible and Hyoid bone correspond to C3.

The thyroid cartilage is from C4 to C5.

The cricoid cartilage is from C6 to C7.

Clinical significance

If it does occur, however, it may cause death or profound disability, including paralysis of the arms, legs, and diaphragm, which leads to respiratory failure.

Common patterns of injury include the odontoid fracture and the hangman's fracture, both of which are often treated with immobilization in a cervical collar or Halo brace.

A common EMS practice is to immobilize a patient's cervical spine to prevent further damage during transport to Medical Aid. This practice has come under review recently as incidence rates of unstable spinal trauma can be as low as 2% in immobilized patients. Canadian studies have developed the Canadian C-Spine Rule (CCR) for physicians to decide who should receive radiological imaging. [Citation needed]

Additional images

References

External links

Category:Bones of the torso Category:Vertebral column