Vertebra

Vertebra is the name for each of the bones that make up the spine.  In humans there are 33 vertebrae in the foetal and childhood and in adulthood there are only 26.  Each is separated from the next smallest by an inter-vertebral disc, except the five vertebrae of the sacrum and coccyx, because of their union.

The vertebrae are aligned with each other by so-called vertebral bodies and their particular processes.  Between a vertebra and another there are groups of connective tissue that are called inter-vertebral discs.

With the exception of the first and second cervical vertebra, the so-called true or movable vertebrae (belonging to the upper three regions) present certain common traits that are best recognized by examining a vertebra in the middle of the thoracic region.

General structure

Except the first and second cervical vertebrae, which have a special configuration, the rest of the vertebrae show a similar structure: the body; vertebral arch; the spine where the muscles are inserted; two pedicles; two transverse processes and four articular processes.
Cervical vertebrae

They are generally small and delicate.  Their spines are small.  They can be differentiated by having a hole at the base of the transverse processes (hole for the vertebral artery).   They are numbered from top to bottom as C1 to C7.

The vertebrae allow the rotation of the neck.  Specifically, the atlas (C1) allows the head to move up and down, and the axis is responsible for the turn of the neck from top to the left and to the right.  Then there is the backbone of rixi (C3) which is the vertebral pattern. The C7 vertebra is known as “Prominent vertebra or Promontory.”  They also have a very wide canal, because it coincides with the beginning of the spinal cord.
Thoracic Vertebrae

Their spines are pointing downward almost vertically, and are smaller in relation to other regions.  They have in their side facets, facet joints connecting with the head of the ribs.  They have a small degree of rotation between them but to be articulated with the rib cage, there is a high degree of mobility.
Lumbar Vertebrae

Vertebrae are more robust because they need to support more weight.  They allow considerable flexion and extension, moderate lateral flexion and a small degree of rotation.  The inter-vertebral discs of the lumbar create what is called the lumbar lordosis (concave curvature) of the spine.  In addition, the process is quadrilateral and is nearly flat.
Embryogenesis

During the first four months of embryonic development, the sclerotome changes its position to surround the spinal cord and notochord.  The sclerotome is formed from the mesoderm and originates in the ventromedial part of the somites.  This column of tissue has a segmented appearance, with parts dense and other less dense areas.

As the sclerotome develops, it condenses more and begins to form what is called the vertebral body.  The development of appropriate forms of the vertebral bodies is regulated by type HOX genes.

The less dense area that separates the sclerotome during development, ends up becoming the inter-vertebral discs.  The notochord disappears (vertebral body), but persist in the region of the inter-vertebral discs as the nucleus pulposus.

The nucleus pulposus and annulus fibers conform inter-vertebral disk primary curves of the spine (thoracic and sacral) during fetal development.  The secondary curves develop after birth.  The cervical curvature is formed as a result of elevation of the head and the lumbar curve as a result of the natural process of walking.  There are several diseases associated with spinal development.

Scoliosis may be the result of an abnormal fusion of the vertebrae.   In Klippel-Feil syndrome, patients have fewer vertebrae than normal along with other birth defects.  A serious flaw in pregnancy may be incomplete closure of the vertebral arch that leads to spina bifida. There are different types of spina bifida that are a reflection of the greater or lesser severity.