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Anatomy of the Spine
Anatomy of the Spine
Your spine is one of the most important parts of your body. It gives your body structure and support. Without it you could not stand up or keep yourself upright. Your spine allows you to move about freely and to bend with flexibility. Your spine also protects your spinal cord. The spinal cord is a column of nerves that connects your brain to the rest of your body, allowing you to control your movements. Without a spinal cord you could not move any part of your body, and your organs could not function.
Keeping your spine healthy is vital if you want to live an active life.
The Spinal Column
The spine is made up of 33 bones (including the sacrum and the coccyx). There are 24 movable bones, called vertebrae. Ligaments and muscles connect these bones together and form what is called the spinal column. The spinal column has three movable segments. From top to bottom they are the cervical spine, the thoracic spine, and the lumbar spine. Each of these segments is discussed in detail below.
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 spine curves slightly outward, and the lumbar spine curves 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 backward "C"-shape-just like the lumbar spine. This type of curve is called a lordotic curve. The cervical spine is much more mobile than the other segments of the spine. Just think about all the directions and angles you can turn your neck and head.
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.
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 about 12 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 to the bones, ligaments, or even the arteries that carry blood to the brain.
The Thoracic Spine (Mid Back)
The thoracic spine is made up of 12 vertebrae. It is located below the top 7 vertebrae of the cervical spine and above the lumbar spine. 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 curve of the thoracic spine is a "C"-shape with the opening of the "C" in the front. This type of curve is called a kyphotic curve.
The thoracic spine has very narrow, thin intervertebral discs. In addition the ribs are connected to the spine in the thoracic segment. These rib connections, combined with the smaller intervertebral discs, limit the amount of movement in the thoracic spine compared to the lumbar or cervical segments of the spine. There is also less space inside the spinal canal.
The Lumbar Spine (Low Back)
The lowest part of the movable spine is called the lumbar spine. This area usually has 5 vertebrae. However, sometimes people are born with 6 vertebrae 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 is shaped like a backward "C", just like the cervical spine. This shape is called a lordotic curve. If you think of the entire spine as having an "S"-like shape, the lumbar region would be the bottom of the "S". The vertebrae in the lumbar spine are the largest of the entire spine. The lumbar spinal canal is also larger than in the cervical or thoracic segments of the spine. The size of the lumbar spine allows for more space for nerves to move about.
When people experience pain in their spine it often occurs in the lumbar region. This is because the lumbar spine is connected to your pelvis, which is where most 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.
There are two SI joints in your pelvis that connect the sacrum (tailbone) and the ilium (large pelvic bone). The SI joints connect your spine to the pelvis, and thus, to the entire lower half of your skeleton.
Like any other joints, there is articular cartilage on both sides of the SI joint surfaces. But unlike most other joints, the SI joints are covered by two different kinds of cartilage. The articular surfaces have both hyaline (glassy, slick) and fibrocartilage (spongy) surfaces that rub against each other. The joints also have many large ridges (bumps) and depressions (dips in the surface that fit together like a puzzle).
The Si joints are also unique in that they are not designed for much motion. It is common for the SI joint to become stiff and actually "lock" as people age. The SI joint only moves about two to four millimeters during weight bearing and forward flexion. This small amount of motion occurring in the joint is described as a "gliding" type of motion. Due to the small amount of movement and the complexity, finding out about the SI joints' motion is very difficult during a physical exam.
Important Structures of the Spine
There are a number of important structures of the spine. Knowing about these structures will help you understand how the spine works and what's happening when a problem develops in the spine. These structures include vertebrae, intervertebral discs, facet joints, neural foraminae, the spinal cord, nerve roots, paraspinal muscles, and spinal segments.
Each disc has a strong outer ring of fibers called the annulus, and a soft, jelly-like center called the nucleus pulposus. The annulus is the strongest area of the disc. It helps keep the disc's center intact. The annulus is actually a strong ligament that connects each vertebra together.
The mushy nucleus of the disc serves as the main shock absorber. The nucleus is made up of tissue that is very moist because it has high water content. The water content is what helps the disc act like a shock absorber-somewhat like a waterbed mattress.
Although you may not think so, the spinal column has real joints just like the knee or elbow. In the spine, these joints are called facet joints. The facet joints link the vertebrae together and give them the flexibility to move against each other. The facets are the "bony knobs" that meet between each vertebra. There are two facet joints between each pair of vertebrae, one on each side. They extend and overlap each other to form a joint between the neighboring vertebra facet joint. The facet joints give the spine its flexibility.
The facet joints are synovial joints, which means they allow movement between two bones. The ends of the bones that make up a synovial joint are covered with articular cartilage, a slick spongy material that allows the bones to glide against one another without much friction. Synovial fluid inside the joint keeps the joint surfaces lubricated, like oil lubricates the parts of a machine. This fluid is contained inside the joint by the joint capsule, a watertight sac of soft tissue and ligaments that fully surrounds and encloses the joint.
The spinal cord branches off into 31 pairs of nerve roots, which exit the spine through small openings on each side of the vertebra called neural foraminae. The two nerve roots in each pair go in opposite directions when traveling through the foraminae. One goes out through the left foramina; the other goes out through the right foramina. The nerve root allows nerve signals to travel to and from your brain to the rest of your body.
The spinal cord is a column of millions of nerve fibers that carries messages from your brain to the rest of your body. It extends from the brain to the area between the end of the first and second lumbar vertebrae. The spinal cord lies within the hollow canal called the spinal canal that is formed when the spinal vertebrae stack on top of each other. The spinal canal holds and protects the entire spinal cord and its nerve roots.
The nerve fibers in your spinal cord branch off to form pairs of nerve roots that travel through the small openings between your vertebrae. The nerves in each area of the spinal cord connect to specific parts of your body. This is why damage to the spinal cord can cause paralysis in certain areas and not others. It depends on which spinal nerves are affected.
The nerves of the cervical spine go to the upper chest and arms. The nerves of the thoracic spine go to the chest and abdomen. The nerves of the lumbar spine go to the legs, pelvis, bowel, and bladder. These nerves coordinate and control all your body's organs and parts, and allow you to control your muscles.
The muscles next to the spine are called the paraspinal muscles. They support the spine and motors to move the spine. Joints allow flexibility, and muscles allow mobility. There are many small muscles in your back. Each controls some part of the total movement between the vertebrae and the rest of the skeleton. These muscles can be directly injured, such as when you have a pulled muscle or muscle strain. They can also cause problems indirectly, such as when they are in spasm after injury to other parts of the spine.
Doctors sometimes look at a spinal segment to understand and explain how the whole spine works. A spinal segment is made up of two vertebrae attached together by ligaments, with a soft disc separating them. The facet joints fit between the two vertebrae, allowing for movement, and the neural foraminae between the vertebrae allow space for the nerve roots to travel freely from the spinal cord to the body. The spinal segment allows doctors to examine the repeating parts of the spinal column to understand what can go wrong with the various parts of the spine.
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IMPORTANT SAFETY INFORMATION
As with any medical treatment, individual results may vary. There are potential risks and recovery takes time. People with conditions limiting rehabilitation should not have this surgery. Only a spine surgeon can tell if spine treatment is right for you.