Last updated: 03/2012

The brain and spinal cord together form the central nervous system (CNS) which is responsible for processing all the information coming from our senses, keeping our organs and reflexes functioning, and directing our movements, thoughts and feelings.

The spinal cord is the critical organ that connects the brain to the rest of the body by conveying electrical impulses along the long nerve fibres that are bundled within it.

The nerves that branch out from the spinal cord to the rest of the body comprise the peripheral nervous system (PNS). These peripheral nerves both receive and convey messages creating a feedback loop that allows us to feel sensation and enable movement.

A nerve cell, or neuron, has a long slender projection, called the axon that acts like a transmission line coming from the control centre of the cell. Even though axons are microscopic in diameter, they may be many feet long. Wrapped around the nerve fibres is a fatty substance called myelin that is similar to insulation on a telephone wire. Myelin is a critical component of the nervous system in that it speeds up the electrical signals and protects the nerves. In addition to neurons, the brain is also home to glial cells which play a critical role in stabilizing the environment, making myelin and supporting and protecting the neurons.

Spinal cord injury (SCI) may occur anywhere from the neck to the lower back. During an initial trauma in which the spinal vertebrae fracture or dislocate, the delicate spinal cord is violently struck. While the cord itself typically remains in one piece, many of the tiny nerve fiber bundles within it are severed. After this initial mechanical injury, inflammation, swelling, and other metabolic processes are triggered, causing further damage and disruption of the nerve fibers. The severity of paralysis experienced by the patient is dependent upon the degree of damage done to the spinal cord. However, even in cases of complete paralysis where the patient has no feeling or movement below the injury, the spinal cord itself is not severed completely, and in fact, there are some axons that remain intact across the injury site. Some of these are thought to have lost their myelin sheaths (their insulation) and therefore do not conduct electrical signals well.

Spinal cord injury affects mostly young adults, about 80% of whom are males. Car accidents are responsible for about 50% of cases. Sporting accidents, serious falls, wounds, and diseases of the spine, such as spina bifida, can also cause permanent injury to the spinal cord. In North America, it is estimated that more than a million individuals live with a disability resulting from some type of spinal cord injury.

Because spinal cord injuries are often the result of terrible accidents which paralyze otherwise fit and mostly healthy young people, they can cause significant and prolonged suffering. Depending on the severity of the injury, rehabilitation may help many people to regain some degree of function.

Unlike the skin, blood, muscle and other organs, for many reasons the CNS does not routinely regenerate after damage hence, the disability caused by spinal cord injury may be permanent and profound. In contrast, the nerves in the PNS tend to regenerate after injury, both because they are intrinsically better programmed to regenerate, and because the cells that myelinate axons in the PNS (called Schwann cells) tend to encourage regeneration.

After spinal cord injuries occur, there is only a small window of opportunity hours, maybe weeks in which therapies may reduce the disability. Restoring the electrical transmission between the brain and spinal cord requires repairing the myelin sheath around the damaged neurons and, in severe cases, the regrowth of severed nerve fibres across the site of injury and into the neural network below the lesion. Scarring and other cellular damage that occurs when the body responds to injury often compounds the difficulties in bridging the lesion site in the aftermath of the injury, and in many cases rehabilitation is the only recourse.

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Spinal Cord Injury - Stem Cell Network