Typical vertebra
A typical vertebra consists of a vertebral body and a vertebral arch. The vertebral body is anterior and is the major weight bearing component of the bone. It increases in size from vertebra CII to vertebra LV.
Fibrocartilaginous intervertebral discs separate the vertebral bodies of adjacent
vertebrae. The vertebral arch is firmly anchored to the posterior surface of the vertebral body by two pedicles, which form the lateral pillars of the vertebral arch. The roof of the vertebral arch is formed by right and left laminae, which fuse at the midline.
The vertebral arches of the vertebrae are
aligned to form the lateral and posterior walls of the vertebral canal, which extends from the first cervical vertebra (CI) to the last sacral vertebra (vertebra SV). This bony canal contains the spinal cord and its protective membranes.
A spinous process projects posteriorly and generally inferiorly from the roof of the vertebral arch.On each side of the vertebral arch, a transverse process extends laterally from the region where a lamina meets a pedicle.
From the same region, a superior articular process and an inferior articular process articulate with similar processes on adjacent vertebrae.
Vertebral canal
The spinal cord lies within a bony canal formed by adjacent vertebrae and soft tissue elements (the vertebral canal):
• The anterior wall is formed by the vertebral bodies of the vertebrae, intervertebral discs, and associated ligaments.
• The lateral walls and roof are formed by the vertebral arches and ligaments.
Within the vertebral canal, the spinal cord is surrounded by a series of three connective tissue membranes (the meninges).
Intervertebral foramina
Each spinal nerve exits the vertebral canal laterally through an intervertebral foramen. The foramen is formed between adjacent
vertebral arches and is closely related to intervertebral joints:
• The superior and inferior margins are formed by notches in adjacent pedicles.
• The posterior margin is formed by the articular process of the vertebral arches and the associated joint.
• The anterior border is formed by the intervertebral disc between the vertebral bodies of the adjacent vertebrae.
Vertebrae
There are approximately 33 vertebrae, which are subdivided into five groups based on morphology and location:
The seven cervical vertebrae between the thorax and skull are characterized mainly by their small size and the presence of a foramen in each transverse process.
The 12 thoracic vertebrae are characterized by their articulated ribs; although all vertebrae have rib elements, these elements are small and are incorporated into the transverse processes in regions other than the thorax; but in the thorax, the ribs are separate bones and articulate via synovial joints with the vertebral bodies and transverse processes of the associated vertebrae.
• Inferior to the thoracic vertebrae are five lumbar vertebrae,which form the skeletal support for the posterior abdominal wall and are characterized by their large size.
Next are five sacral vertebrae fused into one single bone called the sacrum, which articulates on each side with a pelvic bone and is a component of the pelvic wall.
• Inferior to the sacrum is a variable number, usually four, of coccygeal vertebrae, which fuse into a single small triangular bone called the coccyx.
Typical vertebra
A typical vertebra consists of a vertebral body and a posterior vertebral arch. Extending from the vertebral arch are a number of processes for muscle attachment and articulation with adjacent bone.
The vertebral body is the weight-bearing part of the vertebra and is linked to adjacent vertebral bodies by intervertebral discs and ligaments. The size of vertebral bodies increases inferiorly asthe amount of weight supported increases.
The vertebral arch forms the lateral and posterior parts of the vertebral foramen. The vertebral foramina of all the vertebrae together form the vertebral canal, which contains and protects the spinal cord. Superiorly, the vertebral canal is continuous, through the foramen magnum of the skull, with the cranial cavity of the head.
The vertebral arch of each vertebra consists of pedicles and laminae:
• The two pedicles are bony pillars that attach the vertebral arch to the vertebral body.
• The two laminae are flat sheets of bone that extend from each pedicle to meet in the midline and form the roof of the vertebral arch. A spinous process projects posteriorly and inferiorly from the junction of the two laminae and is a site for muscle and ligament attachment.
A transverse process extends postero laterally from the junction of the pedicle and lamina on each side and is a site for articulation with ribs in the thoracic region. Also projecting from the region where the pedicles join the laminae are superior and inferior articular processes, which articulate with the inferior and superior articular processes, respectively, of adjacent vertebrae.
Between the vertebral body and the origin of the articular processes, each pedicle is notched on its superior and inferior surfaces. These superior and inferior vertebral notches participate in forming intervertebral foramina.
Thoracic vertebrae
The twelve thoracic vertebrae are all characterized by their articulation with ribs. A typical thoracic vertebra has two partial
facets (superior and inferior costal facets) on each side of the vertebral body for articulation with the head of its own rib and the head of the rib below.
The superior costal facet is much larger than
the inferior costal facet.
Each transverse process also has a facet (transverse costal facet) for articulation with the tubercle of its own rib. The vertebral body of the vertebra is somewhat heart shaped when viewed from above, and the vertebral foramen is circular.
