The spine is the structure that supports our upright position. The spine is divided into five regions progressing from bottom to top include the coccyx, sacrum, lumbar spine, thoracic, and cervical spine. The cervical spine is the part of the spine in the neck and supports the skull. The thoracic spine, the largest portion, connects to the ribs which makes room for our lungs. The lumbar spine spans the space from the ribs to the pelvis and is considered the low back. The sacrum sits between the hip bones. The coccyx is the very end of the spine and is known as the tailbone.
Understanding the Spine
The spine is a beautifully engineered structure that serves multiple functions. The spine allows movement in a number of directions while at the same time protecting the spinal cord that runs in the hollow, central portion of the spine. Component parts of the spine are important to the normal function of this structure. Damage to different parts of the spine may result in specific problems that cause pain.
The cervical, thoracic, and lumbar spine consists of bones called vertebrae. Seven vertebrae make up the cervical spine, twelve the thoracic spine, and five the lumbar spine. Each vertebra has a weight-bearing, round body in the front and an arch in the back. The vertebrae are stacked like a column of coins, the arches forming a vertical column with a central channel, the spinal canal. The vertebrae have wings (transverse process) and a sail (spinous process) These pieces of bone allow for attachment of muscles and ligaments.
The upper and lower portion of the vertebral arch forms facet joints with the vertebrae below and above. Just like other joints in the body, these articulations contain cartilage, a surrounding joint capsule, and lubricating joint fluid. Facet joints help stabilize the spine while allowing movement forward, backwards, and rotation. The spatial orientation of the facet joints allows for specific motion associated with different parts of the spine. The lateral orientation of the cervical spine facet joints allows neck motion from side to side. The orientation of the thoracic spine joints allows for rotation. The vertical orientation of the lumbar facet joints allows forward bending, more limited backwards bending and little rotation.
At the bottom of the spine, the sacrum attaches to the iliac bones to form the sacroiliac joints.. The top of the sacrum is the first sacral vertebrae or S1. The sacrum contains the end of the spinal canal and the corresponding spinal nerves supplying areas near and between the buttocks.
Ligaments are strong tissue bands that act as a brace around the spine and between its bony attachments. Ligaments lend support while limiting motion. Ligaments line the front and back of the vertebral bodies and discs. This brace helps keep the parts of the spine in proper alignment. The ligament in front of the spine covers the entire area without a break. The ligament in the back of the spine tapers to one half of its size once it reaches the lumbar area. This allows for a greater number of disc herniations in the lower portion of the lumbar spine since the support for discs in this area is much less.
Intervertebral discs separate and cushion the vertebrae at all levels of the spine. The movements in all directions are related to the action of the discs as a universal joint. The annulus fibrosus is the though, outer fibrous layer of the disc. The annulus consists of layers of fibers that run in opposite directions that allow the disk to contract and expand as movement requires. The jelly center in the middle of the disc is the nucleus pulposus . The nucleus pulposus moves side to side, forward and back inside the annulus. The gel moves in the opposite direction of the spine and is a shock absorber.
The spinal cord is the large bundle of nerves that connects the brain with the rest of the body. The cord extends from the cervical spine to the top of the lumbar spine (L-1) and is protected by the bones forming the spinal canal. Within the spinal canal, many smaller spinal nerves branch off from the outer edge of the spinal cord and exit the spinal canal through openings formed by the facet joints known as neural foramina. Each of these spinal nerves has fibers for sensation and muscle function. For example, one spinal nerve supplies each facet joint, another supplies the skin and muscle over the back and another gives sensation to the muscles, bones and skin of the leg on one side of the body.
Normal posture is maintained with muscles that surround the spine as well as playing a key role in the movement of the spine. The largest back muscle runs down the back of the spine from the base of the skull to the sacrum and pulls the spine backward and to the side. Smaller muscles under this large muscle run between the vertebrae and cause the spine to bend to the side and twist. A large muscle in front of the spine attaches the vertebrae with the thighbone. When you bend forward, this muscle is activated. Covering all the muscles of the spine is a membrane or fascia, which acts like plastic wrap. The fascia improves the function of contracting muscles
All parts of the spine are supplied by arteries, capillaries and veins. In the neck, the arteries that supply the back of the brain also supply blood to the cervical spine. The arteries run in holes in the lateral parts of the vertebral bodies until they enter the hole at the base of the skull, the foramen magnum to supply the brain. Neck spinal veins run in channels in the spinal canal and along the lateral portions of the vertebral bodies. Arteries have valves that allow blood flow only away from the heart. Veins are valveless. This lack of valves allows forward and backward flow of blood. This is important in considering the spread of cancer from different areas of the body to involve the spine.
In the lumbar spine, arteries directly originating from the aorta supply the thoracic and lumbar spine. These arteries also supply the nerves in the spinal canal. Veins follow the same course as their corresponding artery. These veins are also valveless. These arteries and veins also supply the muscles surrounding the spine. The importance of this organization of blood supply is that the interruption of blood flow to any component of this system results in a lack of oxygen which is associated with the generation of pain in that structure.
Neighboring structures near the Spine
Structures other than the spine itself can cause neck, arm, chest, low back, or leg pain. Examples of these structures in the neck include the jaw joints, the windpipe, neck lymph nodes, the esophagus, thyroid, and the upper parts of the lungs. In the thoracic spine, the lungs, heart, and aorta are sources of chest pain. A number of organs are placed in front of the lumbar and sacral spine. These organs include the kidneys, ureters, aorta, inferior vena cava, bile ducts, pancreas, lymph nodes, and rectum.