Vertebrae Regional Characteristics

Study Notes

The 33 vertebrae in the vertebral column can be identified by their characteristic features, which are unique to each of the five regions: cervical, thoracic, lumbar, sacrum, and coccyx.
Cervical vertebrae have foramina in their transverse processes, and the C7 vertebra has the longest spinous process, which forms a prominence under the skin at the back of the neck.
The articular facets of thoracic vertebrae are nearly vertical, permitting rotation and lateral flexion of the vertebral column in this region.
Regional variations in the size and shape of the vertebral canal accommodate the varying thickness of the spinal cord.

Cervical vertebrae are the smallest of the 24 movable vertebrae and are located between the cranium and the thoracic vertebrae.
They bear less weight than the larger inferior vertebrae, and their smaller size reflects this.
The cervical IV discs are relatively thick compared to the size of the vertebral bodies they connect.
The cervical region has the greatest range and variety of movement of all the vertebral regions.

T1 has a complete costal facet on the superior edge of its body for the 1st rib and a demifacet on its inferior edge that contributes to the articular surface for the 2nd rib.
T9–T12 vertebrae have some features of lumbar vertebrae, such as tubercles similar to the accessory processes.
Mammillary processes also occur in this region.
Vertebra T12 is a transitional vertebra, with its superior half being thoracic in character and its inferior half being lumbar in character.

The spinous processes of cervical vertebrae can be observed and palpated, especially when the back is flexed and the scapulae are protracted.
The tip of the C7 spinous process is the most evident superficially and is often the only spinous process visible when the patient stands erect.
The spinous process of C2 can be felt deeply in the midline inferior to the external occipital protuberance.
C1 has no spinous process, and its small posterior tubercle is neither visible nor palpable.

Vertebrae begin to develop during the embryonic period as mesenchymal condensations around the notochord.
The mesenchymal bone models chondrify and cartilaginous vertebrae form.
Vertebrae begin to ossify toward the end of the embryonic period (8th week), with three primary ossification centers developing in each cartilaginous vertebra.
Ossification continues throughout the fetal period and infancy.

The IV disc is a cushionlike pad composed of an inner sphere, the nucleus pulposus, and an outer collar of about 12 concentric rings, the anulus fibrosus.
Each nucleus pulposus is gelatinous and acts like a rubber ball, enabling the spine to absorb compressive stress.
The discs are thickest in the lumbar and cervical regions of the vertebral column.
The IV disc permits movement between adjacent vertebrae, and their resilient deformability allows them to serve as shock absorbers.

The vertebral column in adults has four curvatures that occur in the cervical, thoracic, lumbar, and sacral regions.
The thoracic and sacral kyphoses are concave anteriorly, whereas the cervical and lumbar lordoses are concave posteriorly.
The primary curvatures develop during the fetal period and are retained throughout life.
The secondary curvatures result from extension from the flexed fetal position and are maintained primarily by differences in thickness between the anterior and posterior parts of the IV discs.
The curvatures of the vertebral column provide additional flexibility (shock-absorbing resilience), further augmenting that provided by the IV discs.