Spine (Vertebral Column)

What is Vertebral Column

The vertebral column, commonly known as the spine or backbone, is a flexible hollow structure through which the spinal cord runs. It comprises 33 individual small bones called vertebrae, which remain separated by cartilaginous intervertebral discs. The vertebral column forms the axial skeleton, along with skull bones, ribs, and sternum.
These 33 irregular vertebrae are categorized into the following 5 groups:

  1. Cervical vertebrae (7)
  2. Thoracic vertebrae (12)
  3. Lumbar vertebrae (5)
  4. Sacrum (5 fused)
  5. Coccyx (3-4 fused)

Vertebral Column

Where is the Vertebral Column Located

It starts just below the occipital bone and extends up to the tip of the coccyx (tailbone).

Vertebral Column X Ray

Functions

  • The vertebral column encloses the cerebrospinal fluid (CSF), spinal cord, and nerve roots. Thus, it protects the spinal cord from any mechanical injury. Besides, it also protects various vital internal organs, such as the heart and lungs.
  • Several muscles, tendons, and ligaments, which are essential for body movement, attach here.
  • Being the body’s central axis, it bears the whole body weight. It also supports the head, shoulder, and chest. Along with this, it also balances the body by distributing the upper body’s weight to the lower extremities.
  • The joints between the vertebrae, the intervertebral discs, allow the spine to twist and bend. As a result, the spine can flex (bend forward), extend (bend backward), bend sideways, and rotate to some extent.

Anatomy of Vertebral Column

Though the anatomy of all 33 vertebrae differs, each also shares a typical structure. All of them have a vertebral body and vertebral arch.

Vertebral Body

It is the large, cylindrical, weight-bearing component that forms the anterior part of all vertebrae. Its superior and inferior regions are covered by hyaline cartilage. A fibrocartilaginous intervertebral disc separates the adjacent vertebral bodies from each other. As we move down the vertebral column, the size of the vertebral body of each vertebrae increases to support the body’s weight in a better way. 

Vertebral Arch

It forms the lateral and posterior parts of each vertebra. The vertebral arch and vertebral body join to create an enclosed space called the vertebral foramen. These hole-like structures of all the adjacent vertebrae assemble one after the other to form the continuous hollow space of the backbone, the vertebral canal. The spinal cord runs through this canal.

The vertebral arches feature several bony projections, where the muscles and ligaments get attached. They are:

  1. Spinous processes: Every vertebra possesses a spinous process, positioned on the posterior side of the vertebral arch, pointing inferiorly.
  2. Transverse processes: Each vertebra features two transverse processes, extending from the lateral and posterior sides of the vertebrae.
  3. Pedicles: The vertebral body and transverse processes join through this.
  4. Lamina: The transverse and spinous processes of the vertebrae meets here.
  5. Articular processes: Located at the junction between the laminae and pedicles, these processes help form articulations between vertebrae. These processes also contain articular facets at the ends.

Now, let us briefly discuss the 5 groups of vertebrae that make up the spine.

1. Cervical vertebrae

There are 7 cervical vertebrae named C1-C7, having thin intervertebral discs. The first two, C1 (atlas) and C2 (axis), have unique anatomy and help in the rotation of the head. The other five vertebrae, C3-C7, share similar anatomical features. They all have a bifid spinous process, transverse foramina, anterior and posterior tubercles, and a triangular vertebral foramen.

2. Thoracic vertebrae

There are 12 medium-sized thoracic vertebrae (T1-T12) in the spine, with thicker intervertebral discs than cervical ones. As we move down the vertebral column, their size keeps on increasing. Their job is to articulate with the bony ribs, forming the rib cage or thoracic cage.
Each vertebra has two demi facets on either side of its vertebral body, placed superiorly and inferiorly. Through these facets, they articulate with the heads of two different ribs. The transverse processes of the thoracic vertebrae feature a costal facet, where the shaft of a single rib articulates. They also have inferiorly and posteriorly oriented spinous processes and circular vertebral foramen.

3. Lumbar vertebrae

The spine has 5 lumbar vertebrae(L1-L5) supporting the body weight. They have large, kidney-shaped vertebral bodies, triangular vertebral foramen, and short spinous processes. Among the five groups, the lumbar vertebra is the largest.

4. Sacrum

It looks like a single bony component composed of 5 fused vertebrae (S1-S5). It looks like an inverted triangle, with the apex pointing inferiorly.

5. Coccyx

It is another component of the vertebral column, formed by 4 fused vertebrae (Co1-Co4). It articulates with the apex of the sacrum and is devoid of the vertebral canal.

Articulations

  1. Intervertebral symphyses:  All the vertebral bodies, except C1-C2 and S2-S3, are joined via fibrocartilaginous joints by intervertebral fibrocartilage in the form of intervertebral discs. 
  2. Zygapophyseal joints:  These are synovial joints formed between the superior and inferior articular facets of adjacent vertebral arches.
  3. Atlanto-occipital joint: It is another synovial joint found between the atlas (C1) and the occipital bone.

Ossification

The ossification of every vertebra begins around the 8th week of the gestation period. Vertebrae arise from three primary ossification centers: one for the vertebral body and two for the pedicles.

Muscule and Ligament Attachments

Muscle attachments:

  1. Lumbar muscles
  2. Thoracic muscles
  3. Back muscles

Ligament attachments:

  1. Ligamenta flava
  2. Interspinous ligaments
  3. Nuchal ligament
  4. Supraspinous ligament

References

    1. The Vertebral Column — Teachmeanatomy.info
    2. Anatomy, Back, Vertebral Column — Ncbi.nlm.nih.gov
    3. Vertebral column (spine) — Kenhub.com
    4. Vertebral Column — Sciencedirect.com
    5. The Vertebral Column — Courses.lumenlearning.com