Each disc is named according to which two vertebral bodies it lies between. For instance:. The disc and vertebra above and below the disc comprise one segment of the spine - usually called a spinal level or spinal segment. The L4 vertebra and L5 vertebra, along with the disc in between them, make up the L4-L5 segment. Discs are always labeled for the vertebrae that they lie between, and this is consistent throughout the length of the spine - for the cervical, thoracic and lumbar spine.
For example, the C1-C2 disc in the neck lies between the first and second vertebrae in the cervical spine, and the T1-T2 disc lies between the first and second vertebrae in the thoracic spine. See more about Spinal Disc Problems. However, the same is not true of how the spinal nerves are labeled, and back problems are often described by both the spinal segment and the nerve root that is affected.
This is explained in more detail on the next page. The lower back comprises the lumbar spine, which is formed by vertebral bones, intervertebral discs, nerves, muscles, ligaments, and blood vessels.
The spinal cord ends at the top of the lumbar spine, and the remaining nerve roots, called the cauda equina, descend down the remainder of the spinal canal. The lumbar spine has several distinguishing characteristics.
Watch: Lumbar Spine Anatomy Video. While the lumbar spine is sturdy and resilient, it is subject to a high degree of stress and loads, which may cause various problems, resulting in pain. This article provides an overview of the lumbar spine including its anatomy and the potential problems that can occur in this region. When viewed from the side, the lumbar spine has a concave lordotic curve that helps distribute weights and reduce the concentration of stresses.
An increase or decrease in this lordosis may contribute to lower back pain. Read more about Spinal Anatomy and Back Pain. The normal anatomy, as well as potential problems in the lumbar spine, are better understood by focusing on a spinal motion segment. A single lumbar motion segment is comprised of:.
The flexor muscles are in the front and include the abdominal muscles. These muscles enable us to flex, or bend forward, and are important in lifting and controlling the arch in the lower back. The back muscles stabilize your spine. Something as common as poor muscle tone or a large belly can pull your entire body out of alignment.
Misalignment puts incredible strain on the spine see Exercise for a Healthy Back. Vertebrae are the 33 individual bones that interlock with each other to form the spinal column.
The vertebrae are numbered and divided into regions: cervical, thoracic, lumbar, sacrum, and coccyx Fig. Only the top 24 bones are moveable; the vertebrae of the sacrum and coccyx are fused. The vertebrae in each region have unique features that help them perform their main functions. Cervical neck - the main function of the cervical spine is to support the weight of the head about 10 pounds.
The seven cervical vertebrae are numbered C1 to C7. The neck has the greatest range of motion because of two specialized vertebrae that connect to the skull. The first vertebra C1 is the ring-shaped atlas that connects directly to the skull.
The second vertebra C2 is the peg-shaped axis, which has a projection called the odontoid, that the atlas pivots around. Thoracic mid back - the main function of the thoracic spine is to hold the rib cage and protect the heart and lungs.
The twelve thoracic vertebrae are numbered T1 to T The range of motion in the thoracic spine is limited. Lumbar low back - the main function of the lumbar spine is to bear the weight of the body. The five lumbar vertebrae are numbered L1 to L5. These vertebrae are much larger in size to absorb the stress of lifting and carrying heavy objects.
Sacrum - the main function of the sacrum is to connect the spine to the hip bones iliac. There are five sacral vertebrae, which are fused together.
Together with the iliac bones, they form a ring called the pelvic girdle. Coccyx region - the four fused bones of the coccyx or tailbone provide attachment for ligaments and muscles of the pelvic floor. While vertebrae have unique regional features, every vertebra has three functional parts Fig. Each vertebra in your spine is separated and cushioned by an intervertebral disc, which keeps the bones from rubbing together. Discs are designed like a radial car tire. The outer ring, called the annulus, has crisscrossing fibrous bands, much like a tire tread.
These bands attach between the bodies of each vertebra. Inside the disc is a gel-filled center called the nucleus, much like a tire tube Fig.
Discs function like coiled springs. The crisscrossing fibers of the annulus pull the vertebral bones together against the elastic resistance of the gel-filled nucleus. The nucleus acts like a ball bearing when you move, allowing the vertebral bodies to roll over the incompressible gel. The gel-filled nucleus contains mostly fluid. This fluid is absorbed during the night as you lie down and is pushed out during the day as you move upright.
With age, our discs increasingly lose the ability to reabsorb fluid and become brittle and flatter; this is why we get shorter as we grow older. Also diseases, such as osteoarthritis and osteoporosis, cause bone spurs osteophytes to grow. Injury and strain can cause discs to bulge or herniate, a condition in which the nucleus is pushed out through the annulus to compress the nerve roots causing back pain.
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