Back & Spinal Cord LO 4

4. Describe the morphology of a typical vertebrae. Understand the distinguishing features of cervical, thoracic, and lumbar vertebrae. Understand the morphology of the sacrum.

3D Vertebrae

Cervical vertebrae Thoracic and Lumbar vertebrae Sacrum

Most vertebrae consist of two major parts: a body and a vertebral arch.

Body: a somewhat substantial, cylindrical structure that is the anterior-most portion of the vertebra.

Vertebral arch: comprised of two regions: pedicles, which attach to the posterior aspect of the body, and laminae, which extend postero-medially from the pedicles to meet at the posterior midline.

Extending from the arch are three processes:

  • Spinous process: projects posteriorly along the midline, and its inferior slope varies regionally
  • Transverse processes: extend posterolaterally, but this varies regionally
  • Superior and inferior articular processes: variably associated with pedicles and laminae
    • The inferior articular processes are typically associated with laminae
    • The superior articular processes are typically associated with pedicles
    • Inferior articular processes of vertebrae articulate with superior articular processes of successive (inferior) vertebrae. These are known as facet joints.

The space between the superior articular process and the body is the superior vertebral notch, whereas the space between the inferior articular process and the body is the inferior vertebral notch. A pair of superior and inferior vertebral notches together form an intervertebral foramen, which is a lateral opening from the vertebral canal through which a spinal nerve is transmitted.

The vertebral arch and body surround a space, the vertebral foramen, which transmits spinal meninges, the spinal cord, spinal nerves, and associated structures.

Comparing vertebrae types

Special vertebrae

C1 (Atlas) - The first cervical vertebrae, C1 (Atlas), forms that atlanto-occipital joint with the occipital condyles of the occipital bone of the skull. The atlas is unique among vertebrae in that it lacks a body.

C2 (Axis) - The second cervical vertebra, C2 (Axis), forms the atlanto-axial joint with C1. The dens is unique to the axis, and provides a pivot, about which the atlas may partially rotate.

Sacrum - In adults, the sacrum is composed of five fused vertebrae (S1-S5) of decreasing size. This bone articulates with the hip (coxal) bones at the sacro-iliac (S1) joints (laterally), the 5th lumbar vertebra (superiorly), and the coccyx (inferiorly).

Coccyx - In adults, the coccyx is composed of four, fused, and rudimentary vertebrae (Co1-Co4) of decreasing size. This bone is colloquially referred to as the tailbone.