HEAD INJURIES II

Anyone who has watched more than one collegiate or professional football game is familiar with the term “concussion” because it seems as if it is encountered frequently on the field. Despite the improvement in helmet design and rules that are formulated to protect players, concussion is more common than the administrators, coaches, or players admit to. Understanding the anatomy of the nervous system, even at a layman’s level, makes it obvious that concussion will occur as long as one’s head is subject to rapid acceleration and deceleration, and contact against hard surfaces.

The brain sends signals through the spinal cord which then “transfers” these signals through the nerve roots of the cord, to individual nerves. The nerves carry the signals to specialized “nerve hook-ups” in our muscles and the muscles then respond to the commands or signals that the brain gave to them. This is what creates movement. Going in the other direction, the body has special sensory cells that pick up information about the environment and send it back to the brain, very much along the same pathways that took the signals to the muscle. In this way, the brain can process that information and then give additional and appropriate “instructions” to the rest of the body. When we place our hand on a hot stovetop, the special sensory cells in the hand don’t go “ouch”, not immediately. Instead, they “tell” the brain, through the pathway previously described, that “uh, there’s something hot going on over here.” The brain then sends the signal through its nervous system pathways that “tell the hand”, “hey you, move NOW!” Of course, this occurs in milliseconds and this is the very simplified version of things but we have information coming in, signals from the brain going out to the body, and in this way, second to second, we function. The brain can be thought of as a blob that has the consistency of mayonnaise that floats in a fluid that surrounds it. This fluid protects it and prevents the brain from moving too quickly in any direction. If the brain is made to move quickly, it can strike the very hard surface that is the inside of the skull. The skull is supposed to be hard; it’s protecting your brain! The inside of the bony skull is as hard as the outside (according to my father, “Rockhead” was an apt description of my skull and its contents) and if the brain strikes against it, damage can occur.

The damage of concussion can be both easy and difficult to understand. If the head is hit hard or if the player “hits it hard” by making head first contact with another player, there can be damage to the brain at the point of impact. Brain cells can be injured and/or die. This is called a “coup” injury, damage at the point of impact. If the brain is accelerated towards the opposite side of the contact point and damage occurs as it strikes the inside of the skull, this is called a “contrecoup” injury. In both cases, cells are destroyed and we would easily understand that this can cause alteration in function, perhaps enough to say that a concussion has just occurred. What researchers have found, is that it is very difficult to compress the brain enough to cause a lot of damage. It is similar to compressing water or mayonnaise. However, it is relatively easy to injure brain cells by “tearing them apart”. Using our mayonnaise analogy, think how easy it is to “flick” a knife full of mayonnaise off of a big blob of it that may be sitting on a plate. Thus, if the brain is set in motion damage can occur even if contact was not particularly hard.

When we talk about signals or commands being transported from the brain to the body and signals about our environment being brought to the brain, the actual nerve cells do this work. The NEURON or nerve cell has a number of parts but the AXONS are the long “pathways” that can be thought of as the true “information highway”. This is where the rubber meets the road so to speak. The axons are very specialized so that they can carry information from one cell to the other. If an axon is damaged, no information, or incomplete information moves beyond that point. While there have been many theories to explain the basis of concussion and other brain injury, researchers noted that all of them had one thing in common. They considered a lack of oxygen to the cells; structural damage to the cells; changes in the chemical activity of the cells; changes in the electrical activity of the cells; the actual shearing or tearing of cells. The current theory that allowed all of these mechanisms of injury to make sense, was that if the tissue, especially the axons, were stretched or sheared/torn, certain chemical changes followed which caused the alteration in brain function that was called either concussion, or in some cases that were worse, brain injury. The hypothesis that has found acceptance is that the degree of brain injury and dysfunction, will be determined by and predicted by the amount of tissue stretch. The degree of tissue stretch, will determine the amount of metabolic change that occurs. The amount of metabolic change is the key factor in determining the overall long term effect of the injury and the susceptibility to further concussion.