Human Backbone: Definition, Anatomy, and Function

Backbone medical definition

The backbone also called the vertebral column or the spine or the spinal column is the body’s support-giving bony structure comprising a set of flexible bones called vertebrae extending from the base of the skull to the small of the back.

Colloquially, a backbone is defined as the strongest person or part on which a unit depends and indicates character, courage, determination, firmness, and fortitude. The human backbone is just that on which our body depends to maintain posture, stand and walk.

The anatomy of the backbone allows for its main function to protect the spinal cord from damage

Vertebral Column Anatomy

The human backbone is also known as the vertebral column or the spinal column. It is situated towards the dorsal part of the torso. It comprises of a series of bones called the vertebrae of varying sizes extending from the skull to the small of the back. These vertebrae are arranged one above the other and are held in place by the back ligaments and muscles.

The vertebral column is not straight but consists of two forward shallow curves and two shallow backward curves and when viewed from the side, it resembles a soft ‘S’ shape. These curves serve to optimally distribute the mechanical stress when the body is at rest and during movement.

Vertebrae structure

The vertebra has a complex structure comprising of the ventral body towards the anterior side. Posteriorly, it has a Y-shaped arch that extends to form a foramen (opening) for the spinal cord to run.

From it, extend the spinous processes posteriorly and laterally. The posterior spinous process can be felt if you run your fingers down the center of your back. The transverse processes provide attachment to various muscles and tendons of the back.

On the upper and lower side, each vertebra is attached to an intervertebral disc made of cartilage. This cartilaginous intervertebral disc provides cushioning between the two adjacent vertebrae.

The cervical vertebrae are the smallest in size while the lumbar vertebrae are the largest because they have to bear a larger weight of the body.

Intervertebral Disc

The vertebrae are separated by a fibrous cartilage, called the intervertebral disc. This disc acts as a cushion to absorb shock and facilitates the movements of the vertebrae on each other, thereby allowing the various movements of the back, such as bending, etc.

What is the vertebral arch?

The vertebral arch is defined as the circle of bone surrounding the spinal foramen. It consists of a floor at the back of the vertebra, the pedicles, which form the walls and its roof formed by the meeting of the laminae.

The vertebral arches of the successive vertebrae form the spinal canal through which the spinal cord runs downwards.

Vertebrae types and their numbers

Usually, the backbone consists of 33 vertebrae or backbones arranged in convex and concave curves from its upper end to the lower end.

There are five types of vertebrae, which have been typed according to their position in the vertebral column. The different vertebrae are:

  • Cervical vertebrae are the vertebrae in the neck. They are 7 in number. They are numbered as C1 to C7. The first cervical vertebra is called the atlas.
  • Thoracic vertebrae are the vertebrae of the upper back. They are 12 in number and referred to as T1 to T12. The thoracic vertebrae are attached to ribs of either side.
  • Lumbar vertebrae are the vertebrae of the lower back. They  are 5 in number – L1 to L5. They are  largest in size because they have to bear most of the body’s weight. This is the area of the spinal column that causes the most common back pain problems.
  • Sacral vertebrae are the vertebrae of the small of the back and form the sacrum. They are 4 to 5 (S1 to S5) in number and fuse after the age of 26 years to form a triangular structure. The sacrum fits like a wedge between the hip bones. The vertebrae L5 and S1 bear the most weight of the body are prone to the degeneration of the vertebrae and the intervertebral disc.
  • The coccygeal vertebrae form the coccyx and are situated at the lowermost end of the vertebral column, where the vertebral column merges with the hip bone. It consists of 3 to 5 vertebrae, fused together. It is also known as the tailbone.

The spinal cord

The spinal cord belongs to the nervous system and according to the location, the spinal column is divided by nomenclature into five parts.

  • The cervical spine forms part of the spine in the cervical region and from which the cervical nerves emerge on either side.  They are eight in number.
  • The thoracic spine forms part of the spinal cord in the thoracic region and from which 12 thoracic nerves emerge on either side.
  • The lumbar spine forms part of the spinal cord in the lumbar region (lower back) and from which the fine lumbar nerves emerge on either side.
  • The sacral Spine forms part of the spine in the sacral region and from which five sacral nerves  that form the sacral plexus emerge.

As explained above, the vertebrae form a hollow canal called the spinal canal, through which the spinal cord passes. The spinal canal extends from the brain to the coccyx while the spinal cord ends at the level of the L1-L2 vertebrae. It lets out nerves through each joint between the vertebrae to feed the corresponding areas extending from the neck to the foot.

The brain and the spinal cord are surrounded by a fluid called the cerebrospinal fluid (CSF). This fluid acts as a cushion and provides the brain and the spinal cord with nutrients  and eliminates waste matter.

Backbone functions

The vertebral column is the most load-bearing part of the bony system vis-vis functions. Check out its role in the body.

  • Protects the spinal cord and its nerve roots from damage
  • It offers points of attachments (fixation) to the various muscles, tendons and ligaments of the back.
  • The flexibility of the vertebral column helps in the various movements of the body such as bending forwards, backward and sideways and left and right rotation.
  • As all other bones, the vertebrae of the backbone produce red and white blood cells and store vital nutrients, minerals, and lipids.