Spinal cord injury involves damage to the nerves within the spinal canal; most SCIs are caused by trauma to the vertebral column, thereby affecting the spinal cord's ability to send and receive messages from the brain to the body's systems that control sensory, motor and autonomic function below the level of injury.

The spinal cord and the brain together make up the central nervous system (CNS). The spinal cord coordinates the body's movement and sensation.

The spinal cord includes neurons and long nerve fibers called axons. Axons in the spinal cord carry signals downward from the brain (along descending pathways) and upward toward the brain (along ascending pathways). Many axons in these pathways are covered by sheaths of an insulating substance called myelin, which gives them a whitish appearance; therefore, the region in which they lie is called "white matter."

The nerve cells themselves, with their tree-like branches called dendrites that receive signals from other nerve cells, make up "gray matter." This gray matter lies in a butterfly-shaped region in the center of the spinal cord.

Like the brain, the spinal cord is enclosed in three membranes (meninges): the pia mater, the innermost layer; the arachnoid, a delicate middle layer; and the dura mater, which is a tougher outer layer.

The spinal cord is organized into segments along its length. Nerves from each segment connect to specific regions of the body. The segments in the neck, or cervical region, referred to as C1 through C8, control signals to the neck, arms, and hands.

Those in the thoracic or upper back region (T1 through T12) relay signals to the torso and some parts of the arms. Those in the lumbar or mid-back region just below the ribs (L1 through L5) control signals to the hips and legs.

Finally, the sacral segments (S1 through S5) lie just below the lumbar segments in the mid-back and control signals to the groin, toes, and some parts of the legs. The effects of spinal cord injury at different segments along the spine reflect this organization.

Several types of cells carry out spinal cord functions. Large motor neurons have long axons that control skeletal muscles in the neck, torso, and limbs. Sensory neurons called dorsal root ganglion cells, whose axons form the nerves that carry information from the body into the spinal cord, are found immediately outside the spinal cord. Spinal interneurons, which lie completely within the spinal cord, help integrate sensory information and generate coordinated signals that control muscles.

Glia, or supporting cells, far outnumber neurons in the brain and spinal cord and perform many essential functions. One type of glial cell, the oligodendrocyte, creates the myelin sheaths that insulate axons and improve the speed and reliability of nerve signal transmission. Other glia enclose the spinal cord like the rim and spokes of a wheel, providing compartments for the ascending and descending nerve fiber tracts.

Astrocytes, large star-shaped glial cells, regulate the composition of the fluids that surround nerve cells. Some of these cells also form scar tissue after injury. Smaller cells called microglia also become activated in response to injury and help clean up waste products. All of these glial cells produce substances that support neuron survival and influence axon growth. However, these cells may also impede recovery following injury.

After injury, nerve cells, or neurons, of the peripheral nervous system (PNS), which carry signals to the limbs, torso, and other parts of the body, are able to repair themselves. Injured nerves in the CNS, however, are not able to regenerate.

Nerve cells of the brain and spinal cord respond to trauma and damage differently than most other cells of the body, including those in the PNS. The brain and spinal cord are confined within bony cavities that protect them, but this also renders them vulnerable to compression damage caused by swelling or forceful injury. Cells of the CNS have a very high rate of metabolism and rely upon blood glucose for energy these cells require a full blood supply for healthy functioning. CNS cells are particularly vulnerable to reductions in blood flow (ischemia).

Other unique features of the CNS are the "blood-brain-barrier" and the "blood-spinal-cord barrier." These barriers, formed by cells lining blood vessels in the CNS, protect nerve cells by restricting entry of potentially harmful substances and cells of the immune system. Trauma may compromise these barriers, perhaps contributing to further damage in the brain and spinal cord. The blood-spinal-cord barrier also prevents entry of some potentially therapeutic drugs.

Finally, in the brain and spinal cord, the glia and the extracellular matrix (the material that surrounds cells) differ from those in peripheral nerves. Each of these differences between the PNS and CNS contributes to their different responses to injury.

Complete vs. Incomplete What is the difference between a "complete injury" and a "incomplete injury?" Persons with an incomplete injury have some spared sensory or motor function below the level of injury the spinal cord was not totally damaged or disrupted. In a complete injury, nerve damage obstructs every signal coming from the brain to the body parts below the injury.

While there's almost always hope of recovering function after a spinal cord injury, it is generally true that people with incomplete injuries have a better chance of getting some return.

In a large study of all new spinal cord injuries in Colorado, reported by Craig Hospital, only one in seven of those who were completely paralyzed immediately after injury got a significant amount of movement back. But, of those who still had some movement in their legs immediately after injury, three out of four got significantly better.

About 2/3 of those with neck injuries who can feel the sharpness of a pin-stick in their legs eventually get enough muscle strength to be able to walk. Of those with neck injuries who can only feel light touch, about 1 in 8 may eventually walk.

The sooner muscles start working again, the better the chances are of additional recovery. But when muscles come back later - after the first several weeks - they are more likely to be in the arms than in the legs.

As long as there is some improvement and additional muscles recovering function, the chances are better that more improvement is possible.

The longer there is no improvement, the lower the odds it will start to happen on its own.

Statistics Approximately 1,275,000 people in the United States have sustained traumatic spinal cord injuries. Males account for 61 percent of all SCIs and females 39 percent.

For more statistics about spinal cord injury and paralysis read: One Degree of Separation -- Paralysis and Spinal Cord Injury in the United States.

Research and cures Currently, there is no cure for spinal cord injuries. However, ongoing research to test surgical and drug therapies is progressing rapidly. Injury progression prevention drug treatments, decompression surgery, nerve cell transplantation, nerve regeneration, and complex drug therapies are all being examined as a means to overcome the effects of spinal cord injury.

Source: American Association of Neurological Surgeons, Craig Hospital, Christopher and Dana ReeveFoundation, The National Institute of Neurological Disorders and Stroke

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Spinal Cord Injury - Spinal Cord Injury - Paralysis Resource ...

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