What Happens In Human Spinal Cord Injuries?

NOTE: 
Below is an article I was sent that explicitly defines how Tarlov, Perineural and Menigeal Cysts form following trauma.

I am thrilled to have finally found an understandable explination as to why I have Tarlov Cysts, and how I got them from an MVA. That portion of the article is underlined for ease of use for those like me, who are, and have been searching for answers to this question.


ARTICLE:
 
Although the spinal cord is protected by the bony vertebrae of the spinal column, it can still be injured ...with disastrous consequences. According to statistics gathered in 1996 by the National Institutes of Health, more than 10,000 Americans experience spinal cord injuries each year and more than 200,000 are living with permanent paralysis in their arms or legs.

People with spinal cord injuries can also lose sensation and -- depending where along the spinal cord the injury occurs -- control over critical body functions, including the ability to breathe. And because two-thirds of spinal cord injuries occur in people who are 30 years old or younger, the resulting disabilities can affect their entire adult lives.
 
Usually, injuries to the spinal cord injuries do not result in a cut through the cord; instead, they crush the thin, fibrous extensions of nerve cells that are surrounded by the vertebrae. These extensions are called axons, the long, thin strings of nerve cell cytoplasm that carry electrical signals up and down the spinal cord. The axons of nerve cells with similar functions run in groups or pathways. Some carry sensory information upward to the brain; others run downward from the brain to control the body's movements. An injury to the spinal cord can damage a few or many of these pathways. Nevertheless, a person can often recover some functions that were lost because of the initial injury.

The damage that occurs to spinal cord axons within the first few hours after injury is complex and it occurs in stages. The normal blood flow is disrupted, which causes oxygen deprivation to some of the tissues of the spinal cord. Bleeding into the injured area leads to swelling, which can further compress and damage spinal cord axons. The chemical environment becomes destructive, due primarily to the release of highly reactive molecules known as free radicals. These negatively charged ions can break up cell membranes, thus killing cells that were not injured initially. Blood cells called macrophages that invade the site of injury to clean up debris may also damage uninjured tissue. Non-neuronal cells including astrocytes may divide too often, forming a scar that impedes the regrowth of injured nerve cell axons.

The early events that follow a spinal cord injury can lead to other kinds of damage later on. Within weeks or months, cysts often form at the site of injury and fill with cerebrospinal fluid, the clear, watery fluid that surrounds the brain and spinal cord. Typically, scar tissue develops around the cysts, creating permanent cavities that can
elongate and further damage nerve cells. Also, nerve cell axons that were not damaged initially often lose their myelin, a white, fatty sheath that normally surrounds groups of axons and enhances the speed of nerve impulses.

Over time, these and other events can contribute to more tissue degeneration and a greater loss of function. Scientists are trying to understand how this complex series of disruptive events occurs so they can find ways to prevent and treat it. They are also trying to identify treatments that will enhance some of the normal -- but often limited -- kinds of recovery that can occur after a spinal cord injury.

Another complication in spinal cord injury stems from the variety of nerve fibers and cell types that make up the tissue. In the spinal cord, axons run in bundles or pathways up and down the cord. The downward or descending pathways from the brain to the spinal cord carry nerve signals that control voluntary movements. The upward or ascending pathways carry sensory information -- about touch, temperature, pain, and body position -- from the entire body to the brain. Researchers believe that the ascending and descending pathways, as well as different groups of nerve cells (also called neurons) that lie entirely within the spinal cord, may require individualized treatments to regenerate and regain their functions.

"Do the descending motor pathways from the brain into the spinal cord need the same things [for recovery] as sensory fibers that go from the spinal cord to the brain?" asks Barbara Bregman, a neuroscientist in the department of anatomy and cell biology at Georgetown University in Washington, D.C. "It is important to know what the cells need and when they need it."

For example, if scientists are going to be able to devise ways to repair damaged spinal cord tissue, they may need to use special combinations of nourishing proteins -- called neurotrophic factors -- to help damaged axons to regrow and regain some function. The damaged cells may also require a specific environment in which to recover. So researchers study the chemical composition of the non-cellular material -- the extracellular matrix -- that surrounds healthy neurons in the spinal cord and in the peripheral nervous system that serves the rest of the body. Additionally, damaged spinal
cord neurons may require the presence -- or even the absence -- of different kinds of nonneuronal cells for regrowth and functional recovery.

Although scientists are beginning to understand the cellular and molecular events that occur after spinal cord injury, one question continues to dominate the research: Why don't the brain and spinal cord repair themselves?

Additional reading:
1. M. E. Schwab and D. Bartholdi. "Degeneration and regeneration of axons in the lesioned spinal cord." Physiol. Rev. 76 (2): 319-370 (1996).

2. M.E. Schwab. "Bridging the gap in spinal cord regeneration." Nature Med. 2 (9): 976-977. 1996.