The spine is a column of 26 bones that extends in a line from the base of the skull to the pelvis. Twenty-four of the bones are called vertebrae. The bones of the spine include:
- Seven cervical vertebrae in the neck
- Twelve thoracic vertebrae at the back wall of the chest
- Five lumbar vertebrae at the inward curve (small) of the lower back
- The sacrum, composed of five fused vertebrae between the hip bones
- The coccyx, composed of three to five fused bones at the lower tip of the vertebral column.
The vertebrae link to each other and are cushioned by shock-absorbing disks that lie between them. The vertebral column provides the main support for the upper body, allowing humans to stand upright or bend and twist, and it protects the spinal cord from injury. The structures of the spine that are the most involved in spinal stenosis include:
- Intervertebral disks -- Pads of cartilage filled with a gel-like substance that lie between vertebrae and act as shock absorbers.
- Facet joints -- Joints located on the back of the main part of the vertebra, which are formed by a portion of one vertebra and the vertebra above it. They connect the vertebrae to each other and permit back motion.
- Intervertebral foramen (also called neural foramen) -- An opening between vertebrae through which the nerves leave the spine and extend to other parts of the body.
- Lamina -- Part of the vertebra at the back portion of the vertebral arch that forms the roof of the canal through which the spinal cord and nerve roots pass.
- Ligaments -- Elastic bands of tissue that support the spine by preventing the vertebrae from slipping out of line as the spine moves. A large ligament often involved in spinal stenosis is the ligamentum flavum, which runs as a continuous band from lamina to lamina in the spine.
- Pedicles -- Narrow stem-like structures on the vertebrae that form the walls of the front part of the vertebral arch.
- Spinal cord/nerve roots -- A major part of the central nervous system that extends from the base of the brain down to the lower back and that is encased by the vertebral column. It consists of nerve cells and bundles of nerves. The cord connects the brain to all parts of the body through 31 pairs of nerves that branch out from the cord and leave the spine between vertebrae.
- Synovium -- A thin membrane that produces fluid to lubricate the facet joints, which allows them to move easily.
- Vertebral arch -- A circle of bone around the canal through which the spinal cord passes. It is composed of a floor at the back of the vertebra, walls (the pedicles), and a ceiling where two laminae join.
- Cauda equina -- A sack of nerve roots that continues from the lumbar region, where the spinal cord ends, and continues down to provide neurologic function to the lower part of the body. It resembles a "horse's tail" ("cauda equina" in Latin).