Vertebrae or Vertebra

[DEFINITION]

• Any one of the 33 body segments of the spinal column. The spinal vertebrae are comprised of 7 cervical, 12 thoracic (dorsal), 5 lumbar, 5 sacral, and 4 coccygeal vertebrae. In adults, the five sacral vertebrae fuse to form a single bone, the sacrum, and the four rudimentary occygeal vertebrae fuse to form the coccyx.
• A typical vertebrae consists of a ventral bosy and a dorsal or neural arch. In the thoracic region the body bears on each side two costal pits for reception of the head of the rib. The arch which encloses the vertebral foramen is formed of two roots or pedicles and two lamina. The arch bears seven processes: a dorsal spinous process, two lateral transverse processes, and four articular processes(two superior and two inferior). A deep concavity, inferior vertebral notch, on the inferior border of the arch provides a passageway for a spinal nerve. The successive vertebral foramina surround the spinal cord.
• The bodies of successive vertebral articulate with one another and are separated by intervertebral disks, disks of fibrous cartilage enclosing a central mass, the nucleus pulposus. The inferior articular processes of the next succeeding vertebra in the caudal direction. Several ligaments(supraspinous, interspinous, anterior and posterior longitudinal, and the ligamenta flava) hold the vertebrae in position yet permit a limited degree of movement.