The Vertebral Column – Types, Characteristics, Functions

General Characteristics of the Spine

The spine is made of vertebrae that link together to protect the spinal cord.

The vertebral column (also known as the backbone or spine), is a tall, thin organ located dorsally that extends from the base of the spine to the pelvis. It protects the spinal cord and provides a key attachment point for numerous muscle groups.

There are 33 vertebrae in the human spine that are split into four regions that correspond to the curvature of the spine; the cervical, thoracic, lumbar, sacrum, and coccyx. The vertebrae of the sacrum and coccyx are fused, but those of the cervical, thoracic and lumbar regions are separated by intervertebral discs.

Vertebrae are given an alphanumeric descriptor, with the initial letter derived from the region they are located in followed by a digit; the digit increases moving down the region. For example, the most superior cervical vertebra is termed C1 and the most inferior C7, which is then followed by the T1 vertebrae of the thoracic region.

Viewed laterally the vertebral column presents several curves that correspond to the different regions of the column. These are called the cervical, thoracic, lumbar, and pelvic regions.

• The cervical curve covers the region between vertebrae C1 and T2, it is the least marked of all the spinal curves.
• The thoracic curve covers the region between vertebrae T2 and T12.
• The lumbar curve covers the region between vertebrae T12 and L5 and is more marked in the females than in males due to differences in pelvic structure.
• The sacral curve begins at the sacrovertebral articulation, and ends at the point of the coccyx.

The thoracic and sacral curves are termed primary curves because they alone are present during fetal life. The cervical and lumbar curves are secondary curves that are developed after birth; the former when the child is able to maintain an upright posture, the latter when the child begins to walk.

Parts of a Vertebra

A vertebra consists of two parts: an anterior segment, or the vertebral body; and a posterior part, or the vertebral (neural) arch.

When articulated together the vertebrae form a strong yet flexible structure that encloses the vertebral foramen, or opening, where the spinal cord sits. It also provides a base for numerous muscle attachments and articulations with other bones.

The strength and flexibility of this structure is generated by the structure of the individual vertebrae. Comprised of bone and cartilage, the configuration of a vertebra varies based on its location within the body, although there are common features associated with those of the upper region.

A typical vertebra of the upper region of the spine consists of two regions:

1. The anterior vertebral body which is the point of articulation between the vertebrae.
2. The posterior vertebral or neural arch that encloses the spinal cord.

Located between each pair of vertebrae are two laterally located openings:

1. The intervertebral foramina that facilitate access to the spinal cord for nerves and vessels.
2. The intervertebral discs that act as ligaments between the vertebral bodies.

The vertebral arch is formed from two, short, thick processes called pediments that extend posteriorly from the lateral sides of the vertebral body, before joining together at the midline with the laminae.

Vertebral Processes

There are seven processes that project from a typical vertebra.

Four articular processes originate from the joint between the pedicles and laminae, two point superiorly and two point inferiorly.  They interact with the zyhapophysis, a socket for the articular processes, of the adjacent vertebrae to make the spine more stable and to facilitate a small degree of articulation.

A single spinous process projects backwards and downwards from the center of the vertebral arch and it serves as a major attachment point for muscles and ligaments of the back.

The two transverse processes project laterally from the join between the pedicle and lamina and also serve as an attachment point for muscles and ligaments of the back. The transverse processes articulate with the ribs in conjunction with the vertebral body.

Regional Vertebral Characteristics

The vertebrae of the spinal column are divided into five regions: cervical, thoracic, lumbar, sacral, and coccyx.

The vertebrae comprising the spinal column can be divided into five regions, based on the five varying curvatures of the spine. The upper three regions of the spinal column are termed the cervical, thoracic, and lumbar; they contain individually jointed vertebrae. The two lower regions—the sacrum and coccyx, or tailbone—are formed from fused vertebrae.

Upper Vertebrae

Vertebrae are given an alphanumeric descriptor, with the initial letter derived from the region they are located in followed by a digit that increases moving down the region. For example, the most superior cervical vertebrae is termed C1 and the most inferior C7, which is then followed by the T1 vertebrae of the thoracic region.

The cervical region of the spine is the most superior and contains seven small vertebrae. The main function of the cervical region is to facilitate attachment of the skull to the spine, protect the spinal cord over the exposed neck and shoulder region, and support the body.

The twelve thoracic vertebrae are located inferiorly to the cervical region. They are larger than the cervical vertebrae and increase in size moving inferiorly to the lumbar region.

The five lumbar vertebrae are the largest vertebral bones and increase in size when moving inferiorly. The lumbar vertebrae play a key role in supporting the body and facilitating locomotion.

Lower Vertebrae

During childhood the five vertebrae of the sacral region are distinct. In adulthood, the five bones fuse to form the sacrum, although it is still often divided into regions termed S1–S5 based on the formation of the original individual bones. The sacrum functions to support the body and protect organs of the pelvis and lower back.

The final region of the spine is the coccyx or tailbone. As with the sacrum, the coccyx is formed from several vertebrae that have fused together.

As it’s the alternative name suggests, the coccyx forms the basis of a tail that has been lost in humans, although it is incorrect to think of it as a vestigial structure since is a key attachment point for many muscles and ligaments and plays a key role in supporting the body while sitting.

Functions

The vertebral column has four main functions:

• Protection – encloses and protects the spinal cord within the spinal canal.

• Support – carries the weight of the body above the pelvis.

• Axis – forms the central axis of the body.

• Movement – has roles in both posture and movement.

Joints and Ligaments

The mobile vertebrae articulate with each other via joints between their bodies and articular facets:

• Left and right superior articular facets articulate with the vertebra above.
• Left and right inferior articular facets articulate with the vertebra below.
• Vertebral bodies indirectly articulate with each other via the intervertebral discs.

The vertebral body joints are cartilaginous joints, designed for weight-bearing. The articular surfaces are covered by hyaline cartilage, and are connected by the intervertebral disc.

Two ligaments strengthen the vertebral body joints: the anterior and posterior longitudinal ligaments, which run the full length of the vertebral column. The anterior longitudinal ligament is thick and prevents hyperextension of the vertebral column. The posterior longitudinal ligament is weaker and prevents hyperflexion.

The joints between the articular facets, called facet joints, allow for some gliding motions between the vertebrae. They are strengthened by several ligaments:

• Ligamentum flavum – extends between lamina of adjacent vertebrae.
• Interspinous and supraspinous – join the spinous processes of adjacent vertebrae. The interspinous ligaments attach between processes, and the supraspinous ligaments attach to the tips.
• Intertransverse ligaments – extends between transverse processes.