Vertebrae have a common basic shape that changes in the different
segments of the spinal column to adapt to their various static needs.
Every vertebra with the exception of the first cervical (atlas, C1) vertebra has: Parts:
- Vertebral body (corpus vertebrae), which is the anterior expanded part of the vertebra.
- vertebral arch(arcus vertebrae),located posteriorly to the body.It is bounded by the lamina arcus vertebrae and the pediculus arcus vertebrae.
- Vertebral foramen,foramen vertebrale.The vertebral body and arch enclose the vertebral foramen. All the vertebral foramina together form the vertebral canal, which houses the spinal cord. Corresponding to the increasing load, the size of the vertebrae increases from above down.
- Pedicle, Pediculus arcus vertebrae,the portion of the vertebral arch situated anteriorly between the body and transverse process as well as between the superior and inferior vertebral notches.
- Lamina, Lamina arcus vertebrae (vertebralis),the portion of the vertebral arch situated posteriorly between the transverse process and the spinous process.
There are seven(7) processes extending from the vertebral arch,four(4) of which are articular processes,processus articularis, two(2) transverse,processus transversus and one(1) spinous,processus spinosus.
The body and transverse processes of the thoracic vertebrae bear joint facets for the ribs. Every vertebral arch at its origin from the vertebral body is marked above and below by a notch (incisura vertebralis, inferior and superior vertebral notch). The notches of two adjoining vertebrae form the intervertebral foramen,which transmits the spinal nerves.
There are 7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4-5 coccygeal vertebrae. Each of these vertebral groups corresponds to a region of the vertebral column.Vertebral column contains 33-34 vertebrae in total.CERVICAL VERTEBRAE
The seven cervical vertebrae form a flexible framework for the
neck and support the head. The bone tissue of cervical vertebrae is more dense than that found in the other vertebral regions and, except for those in the coccygeal region, the cervical vertebrae are smallest. Cervical vertebrae have features which make them unique from other vertebrae.These features are :
- Large vertebral foramen. Because of this feature, the spinal cord is safest in the cervical vertebrae.
- the presence of a transverse foramen,foramen transversarium in each transverse process.The vertebral arteries and veins pass through this opening as they contribute to the blood flow associated with the brain.
- Cervical vertebrae C2–C6 generally have a bifid, or notched, spinous process. The bifid spinous processes increase the surface area for attachment of the strong nuchal ligament that attaches to the back of the skull.
- The first cervical vertebra has no spinous process.
- The process of C7 is not bifid and is larger than those of the other cervical vertebrae.It can easily be palpated. Therefore, it is sometimes called the vertebra prominens.
The axis (C2) is the second cervical vertebra. On the superior surface of its body, the axis bears a thick vertical process, the dens.The dens carries the anterior and posterior articular surfaces,and its apex.The dens corresponds to the body of the axis during during the developmental process.
clinical application:Muscle, bone, or ligament injury in this portion of the spinal column is relatively common in individuals involved in automobile accidents and sports injuries. Joint dislocation occurs commonly between the fourth and fifth or fifth and sixth cervical vertebrae, where neck movement is greatest. Bilateral dislocations are particularly dangerous because of the probability of spinal cord injury. Compression fractures of the first three cervical vertebrae are common and follow abrupt forced flexion of the neck. Fractures of this type may be extremely painful because of pinched spinal nerves.
Twelve thoracic vertebrae articulate with the ribs to form the
posterior anchor of the rib cage. Thoracic vertebrae are larger
than cervical vertebrae and increase in size from superior (T1) to
inferior (T12). Unique features of thoracic vertebrae are:
- Each thoracic vertebra has a long spinous process,which slops obliquely downward. Facets (fovea) for articulation with the ribs.
- Round vertebral foramen.
- roughly heart shaped body(corpus).
THE LUMBAR VERTEBRAE
The five lumbar vertebrae, vertebrae lumbales(L1-L5), form the lumbar region of the vertebral column. They are characterized by the following structural features:
- Body is large and bean-shaped.
- Spinous processes are flattened and oriented in the sagittal direction.
- Long transverse processes.
- The external border of the superior articular process has a mamillary process.
A laminectomy is the surgical removal of the spinous processes and their supporting vertebral laminae in a particular region of the vertebral column. A laminectomy may be performed to relieve pressure on the spinal cord or nerve root caused by a blood clot, a tumor, or a herniated (ruptured) disc. It may also be performed
on a cadaver to expose the spinal cord and its surrounding meninges.
THE SACRAL VERTEBRAE
The wedge-shaped sacrum provides a strong foundation for the pelvic girdle. It consists of four or five sacral vertebrae that become fused after age 26. The sacrum has an extensive auricular
surface on each lateral side for the formation of a slightly
movable sacroiliac (sak''ro-il'e-ak) joint with the ilium of the
hip. A median sacral crest is formed along the dorsal surface
by the fusion of the spinous processes. Posterior sacral foramina
on either side of the crest allow for the passage of nerves from
the spinal cord. The sacral canal is the tubular cavity within the
sacrum that is continuous with the vertebral canal. Paired superior
articular processes, which articulate with the fifth lumbar
vertebra, arise from the roughened sacral tuberosity along the
The smooth pelvic surface of the sacrum forms the posterior surface of the pelvic cavity. It has four transverse lines denoting
the fusion of the vertebral bodies. At the ends of these
lines are the paired pelvic foramina (anterior sacral foramina).
The superior border of the anterior surface of the sacrum, called
the sacral promontory, is an important obstetric
landmark for pelvic measurements.