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Anatomy of the Lumbar Spine

What exactly is the spine?

The spine is made up of 24 bones, called vertebrae. Ligaments and muscles connect these bones together to form the spinal column. The spinal column gives the body form and function. The spinal column holds and protects the spinal cord, which is a bundle of nerves that sends signals to other parts of the body. The many muscles that connect to the spine help support the upright posture of the spine and move the spine.

The spinal column has three main sections-the cervical spine, the thoracic spine, and the lumbar spine. The first seven vertebrae form the cervical spine. The mid back, called the thoracic spine, consists of 12 vertebrae. The lower portion of the spine, called the lumbar spine, is usually made up of five vertebrae. However some people have a sixth lumbar vertebra.

The normal spine has an "S"-like curve when looking at it from the side. This allows for an even distribution of weight. The "S" curve helps a healthy spine withstand all kinds of stress. The cervical spine curves slightly inward, the thoracic slightly outward, and the lumbar slightly inward. Even though the lower portion of your spine holds most of the body's weight, each segment relies upon the strength of the others to function properly.

Cervical Spine (Neck)

The cervical spine is made up of the first seven vertebrae in the spine. It starts just below the skull and ends just above the thoracic spine. The cervical spine has a lordotic curve, a backward "C"-shape-just like the lumbar spine. The cervical spine is much more mobile than both of the other spinal regions. Think about all the directions and angles you can turn your neck.

Unlike the rest of the spine, there are special openings in each vertebra in the cervical spine for arteries (blood vessels that carry blood away from the heart). The arteries that run through these openings bring blood to the brain.

Two vertebrae in the cervical spine, the atlas and the axis, differ from the other vertebrae because they are designed specifically for rotation. These two vertebrae are the reason your neck can move in so many directions.

The atlas is the first cervical vertebra-the one that sits between the skull and the rest of the spine. The atlas does not have a vertebral body, but it does have a thick forward (anterior) arch and a thin back (posterior) arch with two prominent sideways masses.

The atlas sits on top of the second cervical vertebra, the axis. The axis has a bony knob called the odontoid process, which sticks up through the hole in the atlas. Special ligaments between the atlas and the axis allow for a great deal of rotation. It is this special arrangement that allows the head to turn from side to side as far as it can.

The cervical spine is very flexible, but it is also very much at risk for injury from strong, sudden movements, such as whiplash-type injuries. This high risk of harm is due to the limited muscle support that exists in the cervical area, and the fact that this part of the spine has to support the weight of the head-an average of 15 pounds. This is a lot of weight for a small, thin set of bones and soft tissues to bear. Sudden, strong head movements can cause damage.

Thoracic Spine (Mid Back)

The thoracic spine is made up of the middle 12 vertebrae. These vertebrae connect to your ribs and form part of the back wall of the thorax (the ribcage area between the neck and the diaphragm). The thoracic spine's curve is kyphotic, a "C"-shaped curve with the opening of the "C" in the front. This part of the spine has very narrow, thin intervertebral discs. Rib connections and smaller discs in the thoracic spine limit the amount of spinal movement in the mid back compared to the lumbar or cervical parts of the spine. There is also less space inside the spinal canal.

 

 

 

Lumbar Spine (Low Back)

The lowest part of the spine is called the lumbar spine. This area usually has five vertebrae. However, sometimes people are born with a sixth vertebra in the lumbar region. The base of your spine (called the sacrum) is a group of specialized vertebrae that connects the spine to the pelvis. When one of the bones forms as a vertebra rather than part of the sacrum, it is called a transitional (or sixth) vertebra. This occurrence is not dangerous and does not appear to have any serious side effects.

The lumbar spine's shape has a lordotic curve-shaped like a backward "C". If you think of the spine as having an "S"-like shape, the lumbar region would be the bottom of the "S". The vertebrae in the lumbar spine area are the largest of the entire spine. The lumbar spinal canal is also larger than in the cervical or thoracic parts of the spine. The size of the lumbar spine allows for more space for nerves to move about.

Low back pain is a very common complaint for a simple reason. Since the lumbar spine is connected to your pelvis, this is where most of your weight bearing and body movement takes place. Typically this is where people tend to place too much pressure, such as when lifting up a heavy box, twisting to move a heavy load, or carrying a heavy object. These activities can cause repetitive injuries that can lead to damage to the parts of the lumbar spine.