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Anatomy Library

The spine is comprised of 33 individual bones.  These bones along with the muscles and ligaments that attach to it form what is often referred to as the trunk or core.  A healthy spine provides a stable platform from which most of our movements originate.  Additionally, the spine forms the housing for the spinal cord, which is the primary neurological pathway that connects the brain to the peripheral nervous system.


Cervical Spine (neck)

The first seven vertebrae form the cervical spine and are numbered C1 through C7.  The function of this region of the spine is to support the weight of the head and allow for a wide range of motion.  This is accomplished by two specialized vertebrae know at the atlas (C1) and axis (C2).


The four bones of the coccyx, like the sacrum, are fused.  Often referred to as the tailbone, it functions as an attachment point for muscles and ligaments that form the pelvic floor.

Facet Joints

Facet joints are the bony articulations between vertebrae.  These connections are what allow the bending and twisting motions of the spine.  Each vertebra has four facets, two above (superior) and two below (inferior).

Intervertebral Discs

Situated between adjacent vertebral bodies, intervertebral discs act as shock absorbers in the spine.  They consist of an outer ring, called the annulus and the inner gel-filled nucleus.



Ligaments are the fibrous bands that support the body structures of the body.  The spine has several ligaments that provide stability between the vertebrae and prevent excessive motion.

Lumbar Spine (low back)

The five vertebrae of the lumbar spine are numbered L1 through L5.  The primary function of this region is to bear the weight of the upper extremity.  These vertebrae are larger than the thoracic and cervical vertebrae to facilitate this weight-bearing.


The back muscles generate motion of the spine but also function to provide stability and maintain spinal alignment.  Muscle groups allow for flexion, extension, rotation and also postural control.  They are often collectively referred to as the trunk or core muscles.  Well-conditioned core muscles are important for a healthy spine.

Sacral Spine

The sacrum is a set of five fused vertebrae.  This region connects the spine to the pelvic bones.  This joint is called the sacroiliac joint.

Spinal Cord

The spinal cord is the major neurological pathway of the body.  About 18 inches long, it connects the brain to the peripheral nerves.  Housed inside the spinal canal formed by the vertebral arches of each vertebra, it runs from them brainstem to the lumbar spine.  In the lumbar spine, the spinal cord branches into the cauda equina which continues to the tailbone and then to the legs and feet.

Spinal Nerves

Spinal nerves are the branches that extend from the spinal cord.  Thirty-one pairs in all, they carry messages back and forth from the brain and spinal cord to the rest of the body.  Each pair of spinal nerves exits the spine through a small hole between the vertebrae known as the intervertebral foramen.  The naming of each set of nerves corresponds with the name of the vertebra above which it exits.

Thoracic Spine (mid back)

The twelve vertebrae of the thoracic spine are number T1 through T12.  These bones form joints with the ribs and help to protect vital organs such as the heart and lungs.


The 33 individual bones of the spine are called vertebra.  Every disc is slightly unique.  They all, however, share three common structural features: a vertebral body, vertebral arch, and processes.

Vertebral Arch

The vertebral arch projects posteriorly from the vertebral body, surrounding and protecting the spinal cord.

Vertebral Body

The vertebral body serves to withstand the compression caused by weight bearing.