Spinal Anatomy

Spinal Cord

   The spinal cord is a long, thin, tubular bundle of nerves that extends from the brain. The brain and spinal cord together make up the central nervous system. Enclosed within and protected by the bony vertebral column, the spinal cord transmits of signals between the brain and the rest of the body, and controls numerous reflexes. In the adult, the lower end of the spinal cord usually ends at the first lumbar vertebra (L1), where it devides into many individual nerve roots.

Spinal Canal

   The bones and ligaments are aligned in such a way to form the spinal canal, which protects and supports the spinal cord. The space between the membrane that encases the brain and spinal canal is called the epidural space. This space is filled with tissue, vessels and large veins. The epidural space is important in the treatment of low back pain because it is into this space that medications are sometimes injected in order to alleviate pain and inflammation of the nerve roots.

Spinal Curves

  The normal spine assumes its natural curves to allow for even distribution of weight throughout the spinal system. There are three natural curves providing your spine the ability to keep you straight and upright, specifically, cervical lordosis (neck), thoracic kyphosis (mid-back) and lumbar lordosis (lower back). Alternation of these normal curves or balance of the vertebrae will increase stress and strain on these structures and can contribute to spinal imbalance and deformity.

Vertebrae Numbering

  Vertebrae are the building blocks of the spine. Physicians use a numbering code to number each of the 24 moving vertebra segments in the spine. There are 7 cervical vertebrae which we call our neck. Below the cervical spine are twelve (12) thoracic vertebrae and our ribs wrap around from our front to attach here. The lumbar spine follows immediately below the last thoracic vertebra with an associated pair of ribs. The lumbar spine typically has five vertebrae but may occasionally have four or six vertebrae. Finally, the sacrum and coccyx are comprised of five (5) fused (non-moving) vertebra and four (4) fused vertebrae respectively.

Vertebrae

  A vertebra (plural: vertebrae) is an individual bone in a flexible column which encases and protects the spinal cord. (The true spinal cord actually ends at the L1 level, where it divides into many different nerve roots that travel to the lower body and legs.) An individual vertebra is composed of a central body, arches that protrude from the bottom of the central body and various processes designed to protect it.

  The general structure of a typical vertebra consists of two essential parts: the anterior (front) segment which is the vertebral body and the posterior part, the vertebral arch, which encloses the vertebral foramen. The vertebral arch is formed by a pair of short rounded pedicles and a pair of flattened plates called laminae and supports weight-bearing processes. These spinous processes allow for attachment of muscles and ligaments. The pair of small joints (facet joints) at each level of the spine allows for mobility and helps guide your movement.

  When the vertebrae articulate with each other, the bodies form a strong pillar to support the head and trunk; the vertebral foramina constitute a canal for the protection of the spinal cord. Finally, in between every pair of vertebrae are intervertebral foramina (one of either side) so spinal nerves and vessels can exit the central column.

Intervertebral Discs

  An intervertebral disc is a shock absorber and found between each vertebra. They are designed for weight bearing and stability of the spine. The tough outer fibrous material of each disc is called the annulus fibrosis and the fluid center is called the nucleus pulposus. The disc compresses when weight is put upon them and spring back when the weight is removed. It is the job of the annulus to keep the fluid center where it belongs. Because the center is composed of fluid, pressures can occur inside the disc and can be influenced by various positions and movement. When pressures are put upon the disc, the inner fluid shifts. If the annulus weakens, the nucleus can cause a bulge in the retaining wall. In severe cases, the annulus can be completely disrupted, resulting in a disc herniation, or the liquid leaks from the center to the outside of the annulus. When a disc bulge or herniation occurs and places pressure on the nerve roots that exit the spinal area, it can result in leg pain or numbness.

   Discs are without their own blood supply. The discs receive their blood supply through movement as the soak up nutrients from the fluid surrounding the discs. Repetitive movement, injury and poor posture can inhibit this process and accelerate the gradual degenerative process of the structure and function of the disc over time.

Ligaments

  Your spine is unable to support itself by itself. Ligaments are positioned in front and behind the vertebral bodies to provide additional support and prevent excessive motion. The posterior longitudinal ligament is particularly important because of its susceptibility to damage in the lumbar or lower back region due to poor posture and incorrect lifting mechanics.

Muscles

  Muscles exist to support the spine and to allow for movement. Several muscle groups come together to provide the spine with the necessary strength to perform desired motions. Abdominal muscles and back extensors act as your body’s primary support mechanism to keep you upright. These muscles influence how you move and maintain your posture. The gluteal and quadriceps muscles are needed for proper lifting techniques. Finally, the hamstring and psoas muscles are needed to provide proper flexibility to assume the correct posture. It is the combination of these groups that allow us to maintain health and safety for the spine.

  Muscles are often a significant source of pain in lower back complaints. Pain can result of muscle injury from a certain motions or trauma and results in spasm. Chronic muscle spasms can also result from prolonged improper posture or working habits, which causes excessive strain on the muscles.

What’s It All Mean?

  A good understanding of the various parts and functions of your back anatomy will make it easier to appreciate the importance of proper posture, techniques of body mechanics and principles of work simplification. Your knowledge can help you avoid the abuse and possible re-injury of the discs, facet joints, ligaments and muscles which cause pain.