What Happened to My Brain?
James Norwood, MD
Published: July 01, 2002
This article first appeared in the July 2002 issue of Roadracing World & Motorcycle Technology.
The skull is a wonderful thing, most of the time. Sometimes, though, it gets us into trouble. The fact is, that modern motorcycle helmets are better designed than our skulls for the purpose of protecting our brains. This is because the skull protects only against penetrating injuries to the brain. It keeps us from getting poked in the gray matter by tree limbs, handlebars, and other errant sharp objects. Unfortunately, it does relatively poorly at protecting our brains from the sudden deceleration that occurs when head smacks pavement. The inside of the skull, you see, is not softer than pavement. The result is that when we hit our heads, the brain experiences a sudden stop. This is often followed by a nice bounce within the skull that results in another sudden stop against the part of the skull opposite the original impact. Sort of a two-for-the-price-of-one deal. With the potential for two separate injuries.
Most injuries to the brain happen in two places. There are some relatively sharp little bumps inside the skull near the front of the head and at the temples. As the brain sloshes around in the skull at, say 80 mph, those little bumps can tear the nearby blood vessels that feed the brain and cause some bleeding. The other potential site for damage, and the one most frequently damaged, is right in the middle at the base of the brain. The area called the midbrain is tethered to the nearby skull and a thick membrane called the tentorium. Those structures do not want to move, so they hold the midbrain in place while the big part of the brain, the cerebrum, moves around. The result is a tendency for the midbrain and the structures just above it to try to tear. In fact, a concussion is thought to result from microscopic tearing in this part of the brain. The Reticular Activating System (RAS) is located in the midbrain and is responsible for keeping us awake. Trauma to the RAS puts us to sleep until the crash truck arrives. Also near the midbrain is the area responsible for keeping us breathing. Momentary arrest of respiration is a common effect of a head impact. Fortunately, that function is usually restored in a very short time.
There are a host of potential head injuries that can happen even with a helmet on, but Iím going to discuss the two kinds that you can be sent home from the hospital with. These are concussion and internal bleeding. I discussed the mechanisms of both types of injury already. Concussion comes from trauma primarily in the neighborhood of the midbrain (and, of course, the corpus callosum, for those who are very detail oriented), while bleeding is produced by movement of the brain which either stretches and tears blood vessels or shears them across a bony protuberance.
The spectrum of concussion ranges from just a headache to coma. There is no agreement on how much time separates "just a concussion" from what we would formally call a coma. Six hours has been suggested in a few texts, but this is very arbitrary. Suffice it to say that if you wake up after a few hours and are acting normal within a half hour, weíre going to tell you it was only a concussion. The assumption in a concussion is that the damage was all microscopic and you will be as close to normal afterwards as you were before. There are two things you can count on. You will have a headache. You will not remember what happened right before the crash or the first thing you said when you woke up. This "anterograde" and "retrograde" amnesia is part of every concussion. If it is your friend who has the concussion, you will notice that as he or she wakes up, the eyes open and some fairly odd stuff comes out in the first few sentences. He or she wonít remember saying those odd things. Motor function should return as soon as the sentences start making sense, usually in a minute or so. That is, all the limbs should move under voluntary control. If they donít, itís OK to worry. Occasionally, someone will be dazed for several minutes. As long as they come back to normal, thatís fine. The headache may last 12 hours. Some will experience vertigoóthe world will seem to be spinning around, making them dizzy. This will pass, but could last many hours. One indicator of the severity of brain trauma in a concussion is the length of the period of confusion. Another is the length of time lost to the amnesia. A person who is dazed for 15 minutes and who canít remember the three laps before the crash or the ambulance ride has a fair amount of injury. If the rider recovers completely the same afternoon, it was still "only a concussion," but the amount of microscopic damage is more severe. Over time, some of the lost memory comes back and events closer to the impact and closer to the time the eyes opened will be remembered.
Total recovery of brain function is the hallmark of concussion, but those who have seen "punch drunk" boxers may wonder if there really isnít any damage from a concussion. In fact, there is evidence that some damage may be permanent, even though itís undetectable. Like other organs, the brain can easily compensate for minor organic deficiencies. Thus, some of the microscopic damage could be permanent without being noticed. Some of the damage could even be macroscopic: Severe enough that if you opened the skull and examined the brain, you could (just barely) see it with the naked eye. The brain can "rewire" itself to compensate for some microscopic or macroscopic damage. After a number of blows, however, the sum of the damage from repetitive injury may exceed the brainís ability to compensate and you end up with "dementia pugilistica:" a punch drunk fighteróor racer.
The reason you can be sent home with bleeding inside your head (an intracranial bleed) is that they donít always show up. Sometimes there is no loss of consciousness and no ambulance ride, so there is no CT scan. Sometimes the bleeding is so slight that itís not detected. Whether the blow is to the back of the head or the front, bleeding almost always occurs near the front or the temples. This is because the greatest movement of the brain within the skull is going to be fore-and-aft, causing tearing of the vessels along the sides of the brain or near those bony protuberances I spoke about earlier. The bleeding may epidural or subdural: Either outside or inside the membrane that separates the brain from the skull. I mention it because the doctor might use one of those terms, but for this discussion, they act pretty much the same. The pool of blood acts like a tumor, compressing the brain. If it presses mostly on the front, there will be changes in mood. The patient may anger or cry easily. Headache is usually present and there is often confusion. The same symptoms may also occur with a bleed in the temples, but there will also be at least partial paralysis of one side of the body. The "motor strip" that controls the arm and leg on the opposite side of the body is very close to the artery that runs up the temple, and it will be compressed. Either location of bleeding may cause pressure on the optic nerve, causing problems with functioning of one or both eyes. The typical scenario is brief loss of consciousness (due to concussion) followed by a period of normalcy before the symptoms of bleeding begin. In a really massive bleed, of course, the symptoms will begin virtually immediately and you wonít be leaving the hospital that day.
I said earlier that a helmet is better constructed to protect your head than your skull. Thatís because the problem is acceleration. Or, more properly, deceleration. Itís not the impact that does the big damage; itís the violent movement of the brain. The crush zone in your helmet decreases the rate of deceleration experienced by your brain and thus decreases the damage. Those of us who have small heads often get the best helmets because many manufacturers use the same hard shell for a medium and a small helmet. They just put more Styrofoam in the small, which gives a bigger crush zone.
Going back to Sam Flemingsí questionnaire, headache may be just a bruise inside or outside of the skull. It may also be part of a concussion. Blacked out, memory loss, and concussed are all the same thingóconcussion. There are a large number of head injuries I havenít discussed, but the doctor can answer questions about those at your bedsideóusually to your family, since youíll be asleep. What Iíve talked about in this very brief article are the things you are most likely to take home with you.
Dr. James Norwood is an internal medicine physician in general practice in Murfreesboro, Tennessee. He races a Suzuki SV650 in WERA Southeast Regional events and is licensed as a Novice.
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