Dalley, 10th Edition

77

Vertebrae

Structure and Function of Vertebrae Vertebrae vary in size and other characteristics from one re gion of the vertebral column to another and to a lesser de gree within each region; however, their basic structure is the same. A typical vertebra (Fig. 2.3) consists of a vertebral body, a vertebral arch, and seven processes. 1 The vertebral body is the more massive, roughly cylin drical, anterior part of the bone that gives strength to the column and supports body weight. The size of the bodies increases as the column descends, most markedly from T4 inferiorly, as each bears progressively greater body weight. The vertebral body consists of vascular, trabecular (spongy, cancellous) bone enclosed by a thin external layer of compact bone (Fig. 2.4). The trabecular bone is a mesh work of mostly tall vertical trabeculae intersecting with short,

Parts:

Muscle attachment and movement Functions:

Spinous process (x1) Transverse processes (x2)

2

Articular processes (x4)

Restriction of movement Protection of spinal cord Support of body weight

Vertebral arch Vertebral body

Superior view

horizontal trabeculae. The spaces between the trabeculae are occupied by red bone marrow that is among the most actively hematopoietic (blood-forming) tissues of the mature individual. One or more large foramina in the posterior sur face of the vertebral body accommodate basivertebral veins that drain the marrow (see Fig. 2.29). color), a vertebral arch ( red ), and seven processes: three for muscle attachment and leverage ( blue ) and four that participate in synovial joints with adjacent vertebrae ( yellow ). FIGURE 2.3. Functional components of a typical vertebra, represented by 2nd lumbar vertebra. Components include the vertebral body (bone

1 In contemporary usage, the terms vertebral body and centrum and the terms vertebral arch and neural arch are often erroneously used as syn onyms. Technically, however, in each case, the former is a gross anatomy term applied to parts of the adult vertebrae, and the latter is an embryology term referring to parts of a developing vertebra ossifying from primary cen ters. The vertebral body includes the centrum and part of the neural arch; the vertebral arch is thus less extensive than the neural arch, and the centrum is less extensive than the vertebral body (O’Rahilly, 1986; Standring, 2021).

Vertebral canal

Posterior aspect of epiphysial rim

Pedicle

Compact bone Trabecular (spongy) bone Canal for basivertebral vein

Supraspinous ligament

Lamina

Inferior vertebral "end plate"

Spinous process

NP

AF

AF

Zygapophysial joint

Superior vertebral "end plate"

Interspinous ligament

Trabeculae

Anterior longitudinal ligament Posterior longitudinal ligament Intervertebral foramen

Ligamentum flavum

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Joint capsule of zygapophysial joint

AF

AF

AF Anulus fibrosus NP Nucleus pulposus Intervertebral (IV) disc

NP

Vertebral arches

Vertebral bodies

Medial view of left halves of two adjacent hemisected vertebrae and associated IV discs

FIGURE 2.4. Internal aspects of vertebral bodies and vertebral canal. The bodies consist largely of trabecular (spongy) bone—with tall, vertical supporting trabeculae linked by short horizontal trabeculae—covered by a relatively thin layer of compact bone. Hyaline cartilage “end plates” cover the superior and inferior surfaces of the bodies, surrounded by smooth bony epiphysial rims. The posterior longitudinal ligament, covering the posterior aspect of the bodies and linking the IV discs, forms the anterior wall of the vertebral canal. Lateral and posterior walls of the vertebral canal are formed by vertebral arches (pedicles and laminae) alternating with IV foramina and ligamenta ava.