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6 Kids, Sports, and Concussion of fights that result in a knockout, or ESPN’s classic bouts in which one of the boxers is knocked out. The facemask extends even farther from the center of the head toward the front of the athlete. Similar to boxers, if a football player is struck in the center of his helmet, say just above the left ear hole, again the head will bend down toward the opposite shoulder. Its acceleration will be restrained somewhat by the neck musculature, which will resist bending in that direction. If, however, the football player is struck on the front of his face mask, the head will spin very rapidly in the opposite direction. Therefore, blows dealt to the front of the helmet or facemask are more likely to result in a concussion than a blow dealt to the center of the helmet. It should be pointed out that, while rotational acceleration or spinning of the brain leads to a concussion, the spinning may occur in multiple different directions. For example, imagine a boxer who is struck by an uppercut. If the uppercut lands directly on the under surface of his chin, his head will spin upward, such that his face accelerates from its starting position, facing his opponent, upward, so that ultimately he is facing the ceiling. Thus, his head accelerates or spins in an upward direction. If, however, that same boxer is struck by a right cross that lands on his left cheek, his head would spin over his right shoulder. As opposed to spinning upward, his head would be spinning toward the right. In either case, he could sustain a concussion. So long as the brain is spinning, accelerating in a rotational fashion, a concussion can occur. In life, most blows to the head result in rotational accelerations in several directions. It is rare for an uppercut to land directly in the center of the chin, accelerating the brain perfectly upward. More often the blow is landed on the undersurface of one side of the chin or other, which accelerates the brain upward but also off to the side. Similarly, in most real-life situations, there is both a linear and a rotational acceleration present. It is the rotational compo- nent of the acceleration, however, that causes the concussion. So, now we know that concussion is caused by a rotational accelera- tion or “spinning” of the brain. But what happens to the brain, when it is spun, that prevents it from working properly? To understand that, we must understand a little bit about how the brain works. But first, it will help us to consider some common, everyday phenom- ena that are analogous to the workings of the brain cells. Many readers will be familiar with what happens to a rope when one end is raised and then rapidly lowered. An upside down “U” shape appears in the rope, and travels down its length, until it reaches the end. In this way, an “impulse” can be transmitted from one end of a rope to the other end (Figure 1.1). In some sense, the cells of the brain work similarly. The brain consists of a collection of special cells called nerve cells or “neurons.” These nerve cells control all of our movements, thoughts, and bodily functions such as breath- ing. Each nerve cell consists of a cell body and an axon. The axon is a long, narrow part of the nerve cell used to transmit messages to other parts of the