The Vertebrae

Main Anatomy Index | The vertebral column

The Vertebrae

• The vertebral column forms the skeleton of the back and the main part of the axial skeleton.
• It consists of 33 bones called vertebrae which articulate with each other an anterior and posterior intervertebral joints. The vertebrae are arranged into five regions, but only 24 of them are (7 cervical, 12 thoracic and 5 lumbar) are movable. In adults, the five sacral vertebrae are fused to form the sacrum and the four coccygeal vertebrae are fused to form the coccyx.
• The movable vertebrae are also connected to each other by paired, posterior zygapophyseal joints (facet joints) between the articular processes, and strong anterior and posterior longitudinal ligaments.

Normal Curvature of the Vertebral Column (pp. 323, 326)

• Four curvatures are normally visible in the adult.
• The thoracic and sacral curvatures are concave anteriorly while the cervical and lumbar curvatures are concave posteriorly.

• The thoracic and scaral curvatures are called primary curvatures because they develop during the fetal period.
• The cervical and lumbar curvatures are called secondary curvatures as they are not very obvious until after birth.
• The centre of gravity of the body is located just anterior to the sacral promontory.

Back to top

The Vertebrae

Typical Adult Vertebrae (pp. 327, 329, 331)

• A "typical" vertebrae is composed of two parts, a body and a vertebral arch. Each part has a specific function. Typical vertebrae vary in size and other characteristics from one region to another, and to a lesser degree within each region.

Parts of a Typical Vertebrae

The body is anterior and the vertebral arch is posterior.

The Body (p. 329)

• This is the large, heavy, anterior part which has the form of a short cylinder. It resembles a short long bone.
• Its function, like long bones, is to support weight.
• The bodies of the vertebrae, especially T4 inferiorly, becomes progressively larger in order to bear progressively greater weight.
• Their superior and inferior surfaces are rough and flat, except for the smooth bony rims at their circumferences.
• A nutrient foramen pierces the anterior suface of the body and there is a large foramen on the posteior surface for the exit of the basivertebral vein.

The Vertebral Arch (p. 329)

• The part encloses the vertebral foramen.
• The vertebral arch (neural arch), which is attached on each side of the body, protects the neural tissues from injury.
• The arch if formed by two pedicles (L. little feet) which projects posteriorly to meet two laminae (L. thin plates). The laminae meet posteriorly to form the spinous process.
• Four articular processes and two transverse processes also arise from the vertebral arch.

• The space enclosed the the body and the arch is the vertebral foramen.
• The succession of the vertebral foramina in the articulated vertebral column forms the vertebral canal, which contains the spinal cord and its protective membranes (G. meninges), nerve roots and blood vessels.

• The pedicles of the vertebral arch are short stout processes which are attached to the superior part of the body on each side. These project posteriorly to meet the broad and flat laminae.
• Vertebral notches are formed by indentations of the pedicles. The small notch superior to the pedicle, the superior vertebral notch, varies in size at different levels fo the vertebral column. The inferior vertebral notch is larger. When the two vertebral articulate, the vertebral notches are adjacent to each other and form an almost complete oval bony ring, the intervertebral foramen.

• The laminae of the vertebral arch are broad flat plates of bone that extend posteromedially and slightly inferiorly from the pedicles. They overlap the laminae of the vertebrae below.
• The two laminae form the roof of the vertebral foramen where they unite in the median plane. The spinous process arises from their place of union.
• The laminae are rough on their superior and inferior borders where the ligamentum flava attach.
• The spinal roots, dorsal and ventral, in addition to the spinal cord and meninges, are in the vertebral canal. The spinal ganglia (dorsal root ganglia) are in the intervertebral foramina. The nerve roots join each other at the external border of the intervertebral foramen to form a spinal nerve.

Seven Vertebral Processes (pp. 329, 331)

• There are level-like (the spinous and tranverse processes) and four are articular (the articular processes).

• The spinous process of typical vertebrae project posteroinferiorly, usually in the medial plane, from the place of union of the laminae. They overlap the vertebrae below.
• These processes provide attachments for the interspinous and supraspinous ligaments and many muscles.

• The transverse processes project posterolaterally and slightly superiorly from the junctions of the pedicles and laminae.
• These processes act as levers and provide attachments for the deep back muscles, helping them to increase their leverage on the vertebral column.

• The articular processes (zygapophyses) also arise from the junctions of the pedicles and laminae.
• The superior articular processes project superior and the inferior processes inferiorly. Each process has an articular facet.
• The articulation between the superior and inferior articular facets at the zygopophyseal (facet) joints helps to prevent anterior movement of the superior vertebra on an inferior one, especially in the thoracic and lumbar regions.
• The articular facets allow some flexion and extension as well as varying degrees of lateral flexion and rotation.

Back to top

Regional Characteristics of Vertebrae

The Cervical Vertebrae (p. 331)

• These vertebrae are the smallest of the movable ones and form the bony skeleton of the neck.
• Their distinctive feature is the oval foramen transversarium or foramen of the transverse process. These foramina are smaller in C7 than those of the other cervical vertebrae; occasionally they are absent.
• The vertebral arteries pass through the foramen transversarium except those which transmit only small accessory vertebral veins.

• The vertebral foramen is large in the cervical vertebrae as it houses the cervical enlargement for the spinal cord.
• Cervical vertebrae have the typical vertebral structure, except for C1 and C2.
• The spinous processes of C3 to 6 vertebrae are short and bifid (L. bifidus, divided into two parts).
• The spinous process of C7 (vertebrae prominens) is very long.
• Another characteristic of cervical vertebrae is the almost equal size of their vertebral notches.

• C1 and C2 are atypical vertebrae.
• C1, a ring-shaped bone, is called the atlas. It was named after Atlas, the Titan who is depicted as supporting the Earth on his shoulders (C1 supports the skull).
• The kidney-shaped, concave superior articular facets of C1 receive the occipital condyles.
• The atlas has not spinous process or body; it consists of anterior and posterior arches, each of which has a tubercle and a lateral mass.
• There is a tubercle each on the medial surfaces of the superior articular processes for the transverse ligament, which holds in place the dens of the axis.
• There is also a groove that runs from the foramen transversarium to posterior to the anterior articular processes. This groove is for the vertebral artery as it winds around and enters the skull through the foramen magnum.

• C2 is the strongest of the cervical vertebrae and is called the axis because C1 carrying the skull rotates on it.
• C2 has two large flat bearing surfaces, the superior articular facets, upon which the atlas rotates.
• Its distinguishing feature, however, is the blunt tooth-like dens (G. tooth) is held in position by the transverse ligament of the atlas, which prevents horizontal displacement of the atlas.
• C2 has a large bifid spinous process, which is the first one that can be felt in the posterior groove of the neck (sometimes referred to as the nuchal furrow).

• The reason that C1 and C2 vertebrae are so atypical is because part of the body of C1 is incorporated into the body of C2
• The part of the body that remains with C1 is represented by the anterior arch.
• The part of the body of C1 that is added to C2 forms the dens.
• It rises perpendicularly from the superior surface of its body. It is the pivot around which C1 (carrying the head) rotates.

The Thoracic Vertebrae (pp. 331-2)

• The characteristic feature of these bones are their costal facets for articulation with the ribs. There is one or more facets on each side for the body for articulation with the head of a rib, and one on each transverse process of the superior 10 vertebrae for the tubercle of the rib.
• Their spinous processes are long and slender and the middle ones are directely inferiorly over the vertebral arches of the vertebrae inferior to them.

• The middle four thoracic vertebrae are typical.
• The outline of their bodies from above is heart-shaped and their vertebral foramen are circular.
• Sometimes an impression is visible on the left sides of the bodies of these vertebrae. This is produced by the descending thoracic aorta.
• The articular facets are arranged such that they are the posterior part of an arc, with the centre of the circle near the centre of the body of the vertebrae.

• T1 to T4 vertebrae have some feature of cervical vertebrae.
• T1 is atypical in that it has a long, almost horizontal spinous process which may be nearly as prominent as that of the vertebrae prominens.
• T1 also has a complete costal facet on the superior edge of its body for the first rib and a demifacet on its inferior edge which contributes to the articular surface for the second rib.

• T9 to T12 vertebrae are also atypical in that they have tubercles similar to the lumbar vertebra.

Lumbar Vertebrae (p. 332)

• These bones are in the "small of the back" and their spinous processes are visible when the vertebral column is flexed.
• They are distinguished by their massive bodies, sturdy laminae, and the shickness of the lower trunk in the median plane.
• Their bodies viewed superiorly are kidney-shaped (reniform), and their vertebral foramina vary from oval to triangular.

• The largest of all the movable vertebrae, L5, is characterised by its stout transverse process.
• It is large responsible for the lumbosacral angle between the lumbar region and sacrum. The body weight is transmitted from the massivle L5 vertebra to the base of the sacrum.

The Sacrum and Coccyx

Click here to go to The Sacrum

Back to top