Diffuse Axonal Injury is Major Contributor to Pathology of Concussion
Diffuse Axonal Injury or Multi-Focal Axonal Injury
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Diffuse Axonal Injury is really more multi-focal than diffuse. See the previous page. To try to stay consistent with the way the term is used, we will refer to it by its common name, Diffuse Axonal Injury, or DAI. Concussion can result axonal injury. The first step in understanding axonal injury, is understanding the neuron, which we covered at http://braininjuryhelp.com/neuron-core-brain-cell/ Briefly, the part of the neuron which is most exposed to injury from rotational force mechanism is the axon.
The axon is roughly equivalent to a wire that between a light switch and a light fixture. It may run substantial distances, as long as a full meter. It is thin. It transfers its signal by use of electrical impulses.
The axon is vulnerable to injury when the brain mass begins to slide at different rates as a result of rotational forces. This sliding effect is capable of shearing an axon, like a paper cutter would shear a piece of paper. The term “shearing”, shearing force and shearing injury are all used to describe the damage to the axon from the differential sliding force put on layers of the brain.
The effect of this sliding is that the axon is rapidly stretched which may result in the axon being torn or twisted. Even if the axon is not severed, it may be significantly damaged. To protect axons from damage and to assure that electrical impulse do not stray from the appropriate channel, the axon is protected by insulation. This insulation is called the myelin sheath. The myelin sheath but is made up of a series of glial cells, laid end to end. The glial cells resemble rolls of toilet paper, with the glial cells wrapped many times around the core tube of the axon.
Shearing forces can harm this myelin insulation. When it gets damaged (such as in MS) it can have profound implications for the speed of information transfer within the brain.
No Need for a Head Impact for DAI
DAI can occur without any direct impact on the head. A whiplash motion of the head and neck, most often associated with cervical injuries, can cause DAI. However, the likelihood of significant DAI increases when the head hits something, like a windshield. Yet even though there is a contact with the head, it is not the contact phenomenon which causes the injury, but rotational twisting of the brain cells and tracts.