Spine (Vertebral Column)

What is the Vertebral Column?

The vertebral column, also known as the spine, spinal column, or backbone, is a flexible hollow structure within which the spinal cord is located. It is composed of 33 small bones called vertebrae, which are separated by cartilaginous intervertebral discs. The vertebral column forms the axial skeleton, skull bones, ribs, and sternum.

Where is the Vertebral Column Situated?

The spine begins just below the occipital bone and extends to the tip of the coccyx (tailbone).

X-ray of the Vertebral Column

What are the Vertebrae of the Spine?

The 33 irregular vertebrae are divided into the following 5 groups:

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

Vertebral Column (Spine)

Functions

• Shields the spinal cord from mechanical injury by encasing the cerebrospinal fluid (CSF), spinal cord, and nerve roots. It also protects various vital internal organs such as the heart and lungs.
• Serves as the attachment point for several muscles, tendons, and ligaments, which are crucial for body movement.
• Acts as the central axis of the body, bearing the entire body’s weight. It also supports the head, shoulder, and chest, and distributes the upper body’s weight to the lower extremities, balancing the body.
• Enables the spine to flex (bend forward), extend (bend backward), bend sideways, and rotate to some extent, through the joints between the vertebrae, the intervertebral discs.

Parts and Anatomy

Although the anatomy of the 33 vertebrae may differ in some ways, most of them share a typical structure with the following components:

1. Vertebral Body

This 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. The size of the vertebral body increases as we move down the vertebral column to better support the body’s weight.

2. 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 stack up to form the continuous hollow space of the backbone, the vertebral canal, through which the spinal cord runs.

The vertebral arch features the following bony projections, where the muscles and ligaments get attached.

• Spinous processes
• Transverse processes
• Pedicles
• Lamina
• Articular processes

Parts of the Vertebral Column

Anatomy of the Spine

1. Cervical Vertebrae

The spine contains 7 cervical vertebrae named C1-C7, with thin intervertebral discs. The first two, C1 (atlas) and C2 (axis), have unique anatomy and aid in the rotation of the head. The remaining 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

The spine has 12 medium-sized thoracic vertebrae (T1-T12), with thicker intervertebral discs compared to the cervical ones. The size of the individual vertebra increases gradually down the spine. Their function is to articulate with the bony ribs, forming the rib cage or thoracic cage.

3. Lumbar Vertebrae

The spine contains 5 lumbar vertebrae (L1-L5) that support the body weight. They have large, kidney-shaped vertebral bodies, triangular vertebral foramina, and short spinous processes. Among all the vertebrae, the L5 lumbar vertebra is the largest.

4. Sacrum

It resembles a single bony structure composed of 5 fused vertebrae (S1-S5) and has an inverted triangle shape, with the apex pointing downward.

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 lacks the vertebral canal.

Spinal Curves

In adults, the spine has multiple natural curves, with the thoracic and sacrococcygeal curves being the primary ones. There are two other minor curvatures, the cervical and lumbar curves, located in the respective regions of the spine.

These curves provide additional strength to the spine, enabling it to support and distribute the body’s weight, absorb shock, and facilitate bending and movement in different directions.

Articulations

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

Ossification

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

Muscle 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