Anatomy of the Spine
by Amber Donda, PT
The spine consists of 24 bones that are stacked on top of each other to make up 3 regions; Cervical (neck), Thoracic (middle), and Lumbar (lower back). The individual bones in each of these regions are known as vertebrae. Between the vertebrae are gel-like discs. These discs are made up of a strong outer ring known as the annulus and a gelatinous center known as the nucleus pulposus. The role of the discs are to provide cushion between the vertebrae and to absorb pressure from the force of gravity and impact. At the base of the spine, just below the lumbar region, is the sacrum. Unlike the cervical, thoracic, and lumbar regions, the vertebrae of the sacrum are fused and have no discs. When viewing it from the side, your spine has a natural “S” – like curve which allows for even weight distribution. Each segment relies upon the strength of the others to function properly.
Each vertebrae is similar in structure consisting of a base called the body, interlocking facet joints, and a spinous process. The facet joints are “bony knobs” that join the vertebrae together and give them the flexibility to move against each other. Ligaments, which connect bone to bone, help to hold the vertebrae together as well. In the center of each vertebra is a hole which forms a hollow tube known as the spinal canal, which houses and protects the spinal cord and its nerve roots. The nerve roots exit through the neural foramen which is the opening between each two vertebrae.
The structures that provide stability to the spine are known as ligaments and muscles. Ligaments are made up of fibrous connective tissue that connect bone to bone. Muscles are contractile tissues that connect to the bone via a tendon. There are five main ligaments that stabilize the spine in varying ways, including the: anterior longitudinal, posterior longitudinal, interspinous, and supraspinous ligaments, as well as the ligamentum flavum. The main muscular stabilizer in the front of the spine is the transverse abdominis and the main muscular stabilizers in the back of the spine are the multifidi and the erector spinae group (Iliocostalis, Longissimus, and Spinalis). The ligaments and muscles of the cervical, thoracic, and lumbar spine work in tandem to hold the spine upright, provide stability, and allow your body to move.