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Back Anatomy

The Spinal Column:

The spinal column (also called the vertebral column) contains and protects the spinal cord and supports the body and head. The spinal column is flexible to allow movement of the body.

The spinal column is comprised of a column of small bones called vertebrae.

Shock absorbing discs separate the vertebrae.


The 24 vertebrae are named according to their location along the spine. We start out with 33 vertebrae but the lowest nine fuse together to form single bones- 5 fused vertebrae form the sacrum and 4 tiny fused vertebrae form the coccyx (tailbone).

The 24 True or Movable Vertebrae:

Cervical spine (neck area) with 7 vertebrae (labeled C1 - C7)

Thoracic spine (chest area) with 12 vertebrae (labeled T1 - T12)

Lumbar spine (lower back) with 5 vertebrae (labeled L1 - L5)

Fused Vertebrae (Below the lumbar spine):

Sacrum: a triangular shaped solid base with 5 fused vertebrae - connects with the pelvis

Coccyx: (the tailbone) with 4 very small fused vertebrae.

spinal column 3 views

Main Parts of a Vertebra:

The two main parts of the vertebra are the vertebral bodyand the vertebral arch.

Vertebral Body:The anterior segment and largest part of a vertebra, basically cylindrical in shape.

Vertebral Arch:The posterior part of a vertebra; the vertebral arch has several processes (bony projections).

Processes (bony projections) of the Vertebral Arch:

The spinous process (projecting from the center of the vertebral arch) and the transverse processes (projecting from either side of the vertebral arch) serve as attachments for the muscles and ligaments.

The articular processes meet and interlock at thefacet joints to link one vertebra with the next. Each vertebra arch has four (two superior and two inferior) articular processes.

model of three vertebrae

Intervertebral Foramen (plural: intervertebral foramina):

The opening formed between adjacent vertebrae from which the spinal nerves exit. There is an opening on each side.

Facet Joints:

Facet joints (commonly called spinal joints) join adjacent vertebrae. Facet joints are hinge-like and allow adjacent vertebrae to move on one another to allow bending and twisting and also keep the spine within a normal range of motion. The surfaces of the bones that make up the facet joints are coated with smooth cartilage that allows the bones to glide smoothly against each other. Muscles, ligaments and discs support the joints of the spine.


The vertebral bodies are separated by shock absorbing intervertebral discs. Theses discs have a tough outer coating with and contain a jelly-like substance.

Spinal Cord:

A part of the central nervous system, the spinal cord transmits messages from the brain to other parts of the body and vice versa.The spinal cord begins at the brain and runs down to the level of the second lumbar vertebrae. Three meninges (membranes) cover the spinal cord. Spinal nerves branch out form the spinal cord.

Cauda Equina:

The spinal nerve roots continue beyond the lower end of the spinal cord, within the spinal canal. This collection of nerves resembles a horse's tail and is called the cauda equina.


The three membranes enclosing the spinal cord and brain - the pia mater, arachnoid, and dura mater. The dura mater is the outermost and toughest of the three meninges.

Sciatic nerve:

A sensory and motor nerve, the sciatic nerve originates in the lumbar and sacral areas of the spinal column. The sciatic nerve is formed by several nerve roots that extend beyond the lower end of the spinal cord and converge. (The spinal cord at the second lumbar vertebrae). Its two branches run through the pelvis, deep into each side of the buttocks, through the hip, the backside of the upper leg down to the foot. . The sciatic nerve is the largest nerve in the human body - the diameter of a finger.

Spinal Canal:

Spinal Canal (also called vertebral canal) is the large canal in the center of the spinal column that contains the spinal cord and its membranes.


Ligaments are tough bands of connective tissue that connect the vertebrae. Facet joints and ligaments help protect the spine by limiting how far the spine can bend or twist.


Muscles support the spine and allow movement. Muscles of the back, abdomen and buttocks stabilize the spine and maintain proper posture. Muscles protect the spine by absorbing shock before it reaches the discs and facet joints.