Vertebral Column

Vertebral Column

General Characteristics

• The vertebral column consists of 33 vertebrae (7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 fused coccygeal vertebrae). It protects the spinal cord, supports the weight of the head and the trunk, and allows the movement of the rib cage for respiration by articulating with the ribs.
• The primary curvatures are located in the thoracic and sacral regions and develop during embryonic and fetal periods, whereas the secondary curvatures are located in the cervical and lumbar regions and develop after birth and during infancy.

Typical Vertebra

• Consists of a body and a vertebral arch with several processes for muscular and articular attachments.

1. Body

• Is a short cylinder, supports weight , and is separated and also bound together by the intervertebral disks , forming the cartilaginous joints.
• Has costal facets or processes of the thoracic vertebrae anterior to the pedicles, which articulate with the heads of the corresponding and subjacent (just below) ribs.

2. Vertebral (neural) arch

• Consists of paired pedicles laterally and paired laminae posteriorly.
• Forms the vertebral foramen with the vertebral body and protects the spinal cord and associated structures.

3. Processes associated with the vertebral arch

Spinous process

• Projects posteriorly from the junction of two laminae of the vertebral arch.
• Is bifid in the cervical region, spine-like in the thoracic region, and oblong in the lumbar region.

Transverse processes

• Project laterally on each side from the junction of the pedicle and the lamina; articulate with the tubercles of ribs 1 to 10 in the thoracic region.
• Have transverse foramina in the cervical region.

Articular processes (facets)

• Are two superior and two inferior projections from the junction of the laminae and pedicles.
• Articulate with other articular processes of the arch above or below, forming plane synovial joints.

Mamillary processes

• Are tubercles on the superior articular processes of the lumbar vertebrae.

Accessory processes

• Project backward from the base of the transverse process and lateral and inferior to the mamillary process of a lumbar vertebra.

Foramina associated with the vertebral arch

Vertebral foramina

• Are formed by the vertebral bodies and vertebral arches (pedicles and laminae).
• Collectively form the vertebral canal and transmit the spinal cord with its meningeal coverings, nerve roots, and associated vessels.

Intervertebral foramina

• Are located between the inferior and superior surfaces of the pedicles of adjacent vertebrae.
• Transmit the spinal nerves and accompanying vessels as they exit the vertebral canal.

Transverse foramina

• Are present in transverse processes of the cervical vertebrae.
• Transmit the vertebral artery (except for C7), vertebral veins , and autonomic nerves.

Intervertebral Disks

• Form the secondary cartilaginous joints between the bodies of two vertebrae from the axis to the sacrum (there is no disk between the atlas and axis ).
• Consist of a central mucoid substance (nucleus pulposus ) with a surrounding fibrocartilaginous lamina (annulus fibrosus ).
• Comprise one fourth (25%) of the length of the vertebral column.
• Allow movements between the vertebrae and serve as a shock absorber.
• Are avascular except for their peripheries, which are supplied from adjacent blood vessels.

Nucleus pulposus

• Is a remnant of the embryonic notochord and is situated in the central portion of the intervertebral disk.
• Consists of reticular and collagenous fibers embedded in mucoid material .
• May herniate or protrude through the annulus fibrosus, thereby impinging on the roots of the spinal nerve.
• Acts as a shock-absorbing mechanism by equalizing pressure.

Annulus fibrosus

• Consists of concentric layers of fibrous tissue and fibrocartilage.
• Binds the vertebral column together, retains the nucleus pulposus , and permits a limited amount of movement.
• Acts as a shock absorber.

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