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The human spine is a bony structure which houses and protects the spinal cord, and serves as the place of origin for the peripheral spinal nerves. In addition to this protective function, the spine is designed to provide both stability and flexibility to the trunk in multiple planes.

The human spine is divided into four areas that fall between the head and pelvis. These four sections (from the head down) are the cervical spine (neck), thoracic spine (mid back), lumbar spine (low back), and sacrum (part of the pelvis). Each of these areas is unique in both design and function.

Common to the cervical, thoracic, and lumbar regions of the spine are the following anatomical structures.

• Bony Vertebrae

• Facet Joints

• Intervertebral Disc

• Spinal Nerves

• Ligaments

• Muscles


The vertebrae are the bony building blocks of the back and spine. They are designed to protect the spinal cord, provide support and structure to the spine, and carry the weight of the head and trunk. The vertebrae of each section of the spine vary because they have different functions specific to that area.

Cervical: There are seven cervical vertebra and they are the smallest and most mobile in the body.

Thoracic: The 12 vertebrae in the thoracic spine are larger and less mobile. The thoracic vertebrae are the origin of the twelve ribs of the thoracic cage, which serve to protect the vital organs of the body (for example: lungs, heart, liver, kidneys etc.)

Lumbar: The five lumbar spine vertebrae are the largest in the body. They are more mobile than the thoracic vertebrae, but are less mobile than the cervical vertebrae. Lumbar vertebrae are designed to support the weight of the trunk and connect the upper half of the body to the pelvis and legs.

Some common conditions of the vertebra include spinal compression fracture, spondylolisthesis, ankylosing spondylitis, osteoporosis and spondylosis.

Facet Joints

Each vertebral level of the spine has two facet joints, which connect one vertebra to the other. The function of the facet joints is to provide support, stability and mobility to the spine.

The facet joints all have articular cartilage that covers the ends of the bones. The articular cartilage has a smooth and shiny surface, which allows the ends of the bones to slide freely over each other. In addition, each joint is surrounded by a soft tissue protective sleeve called a capsule and is lubricated by synovial fluid.

Common conditions of the facet joints include spondylosis, osteoarthritis of the spine, facet joint inflammation, degenerative joint disease of the spine and facet arthropathy.

Intervertebral Disc

The intervertebral disc is a fibrocartilaginous structure located between the bodies of adjacent vertebra. There is a disc between each pair of vertebra in the spine except between the first and second cervical level.

The disc is similar to a jelly donut. It has a series of outer fibrous rings (annulus fibrosis) surrounding a gelatinous center (nucleus pulposus). The disc functions as a cushion, allows movement, and serves as a cartilaginous joint between adjacent vertebrae.

Common conditions of the intervertebral disc include bulging disc, herniated disc, prolapsed disc, degenerative disc disease, anular tear of the disc, ruptured disc and slipped disc.

Intervertebral Foramen

When the intevertebral disc and fact joints connect two vertebral bodies they form canals on either side of the spine. These canals are called intervertebral foramina. The nerves leaving the spinal cord travel through the foramina, exiting the spinal column, and travel out to the body.

The size or diameter of the spinal foramina can vary from person to person. Any compromise or encroachment of the canal may put pressure on the exiting nerve. This may produce symptoms varying from pain, tingling, numbness or even weakness.

Some conditions affecting the intervertebral foramen include spinal stenosis, spinal osteoarthritis and degenerative joint disease

Spinal Nerves

The spinal nerves are the electrical wires of the body. They originate at the spinal core and exit the spinal column through the intervetebral foramen. Once out in the body, the spinal nerves are considered peripheral nerves. They provide both sensation (afferent) and motor (myotomal) innervations to the body.

Damage or interference with the conduction (ability to transfer information) of these nerves can cause neurological problems such as pain, weakness, abnormal sensations and changes in spinal reflexes.

Common spinal nerve conditions include nerve root entrapment, adhered nerve root, pinched nerve, stinger, sciatica, lumbar radiculopathy and cervical radiculopathy.

Spinal Ligaments

Ligaments are fibrous bands of soft tissue that attach bone to bone. In the spine there are two classifications of ligaments, called the intrasegmental and the intersegmental. Intrasegmental ligaments attach and hold individual vertebra to each other. Intersegemental ligaments attach to and hold many vertebra together.

Ligaments in the spine are vital in providing stability and structure to the spine. They also allow for movement in different planes. The ligamentous system of the spine protects the intervertebral discs from injury, and prevents excessive movement of the spine.

The major ligaments of the intrasegmental group are the ligamentum flavum, interspinous ligament and the intertransverse ligaments. The major ligaments of the intersegmental ligaments include the anterior longitudinal ligament, the posterior longitudinal ligament and the supraspinatous ligament.

Spinal Muscles

The muscular system of the spine is large and complex, including the deep erector spinae or paraspinal muscle groups that run parallel to the spine. In addition, there are the more superficial muscles that help to move and protect the spine. Each area of the spine has a group of muscles that serve to support, move and stabilize it.

The spinal muscles work together with the ligaments to provide movement, stability, and postural support to spine. They can be categorized according to their function. The four basic categories are the flexors, extensors, lateral flexors and rotators.

Muscles can be multisegmental connecting and attaching to more than one vertebra or muscles that support and move one segment in relation to another. Irritation or injury of the structures of the spine may produce spasm and pain in the muscles of the back. Injury, tightness, or weakness of the muscles of the spine can result in pain, decreased ability to maintain good posture, limit movement and reduce ability to stabilize the spine during activity.

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