Concussion: Temporary Power Outage

One of the most dramatic conditions in medicine is the concussion – the total and immediate paralysis of brain function that follows a blow to the head. Typically, the victim  loses consciousness and all reflexive muscle activity for seconds to moments. Blood pressure and heart rate may fall and breathing might stop, effects that are usually brief and unnoticed but which on rare occasion cause immediate death. As consciousness returns, the victim seems confused. He does not recall the fall or the blow. Depending on the seriousness of the injury, he suffers a variable period of time during which he remembers nothing new. He asks repetitive questions about what happened and may seem aggressive or out of character. Normality may reassert itself quickly after a concussion, but sometimes several weeks or months of irritability, insomnia, mood change, headaches, and dizziness follow. In other cases, a period of normality, the lucid interval, may be followed by headache, confusion and drowsiness, indicating more severe trauma to the brain and its surrounding tissues.

Concussion of some degree occurs in almost all “closed head injuries,” defined those in which there are no skull fractures or penetrating injuries to the brain. Depending on the trauma involved, symptoms vary from momentary stunning to prolonged coma, but the mechanism of initial paralysis of brain function is always the same. Understanding that mechanism makes it easier to understand delayed worsening and persistent symptoms that sometimes occur afterwards.

How concussions happen

Concussions happen because the brain has the consistency of Jello and is only loosely tethered inside the rigid skull, mainly at the base. When the head accelerates after a blow, or decelerates because of a fall, the brain keeps moving after the skull has stopped. First the cerebral hemispheres slam into the skull in one direction, and then they rebound in the opposite direction. The temporal lobes, where memories form, are particularly vulnerable to impact damage.

Loss of consciousness, however, comes from movement of the tiny brain stem, which emerges from beneath the two large cerebral hemispheres and connects them with the spinal cord. As the heavy cerebral hemispheres above move, the brainstem bends, rotating first in one direction and then in the other. Inside the midbrain, the top part of the brainstem, a group of cells called the reticular activating system reacts with shock and shuts down all communication between brain and body. The power failure lasts anywhere from seconds to weeks, depending on  the degree of rotational force in the midbrain and the amount of stretching and shearing  of nerve cell connections.

Added Problems

Prolonged symptoms, however , usually indicate more widespread damage to the brain in the form of contusions (bruises) and hemorrhages, which cause delayed swelling and worse symptoms. In addition, bleeding from small veins on the surface of the brain (subdural hemorrhage) or between the skull and the dura mater, the tough fibrous lining around the brain (epidural hemorrhage) can occur after seemingly minor concussions. The bleeding stretches, then ruptures more blood vessels, and the growing accumulation of blood puts increasing pressure on the brain.  In 2009, the actress Natasha Richardson died from this kind of complication, soon after a relatively minor fall while skiing. Ronald Reagan suffered  much slower development  of a subdural accumulation of blood following a fall from a horse. Surgical evacuation of the accumulated blood returned him to normal.

After The Concussion

After a head injury, it is very important for the victim to be accompanied by someone who knows him, in order to alert medical personnel to subtle changes in personality or cognitive ability. Most people suffering loss of consciousness will undergo CT or MRI scans, though this is probably unnecessary in mild cases in which the victim has returned to normality quickly. But even after a normal scan, observation, including waking and checking the victim every few hours at night for the first 24 hours, is prudent. If confusion persists after a concussion, the victim should be hospitalized until it clears, and observed carefully after discharge for 24-48 hours.

Most post concussive symptoms like headache, insomnia, irritability and lightheadedness resolve over a few months, requiring only simple medications like ibuprofen and sensible habits such as avoiding alcohol, eating well, sleeping enough, exercising and managing stress.

Repetitive concussions over a lifetime, as suffered in a sport like boxing, clearly damage the brain, producing decline in memory and cognitive abilities, as well as slurred speech and motor symptoms resembling Parkinson’s disease. Recent research suggests that brain injuries may induce progressive change some brain proteins, producing, over a long period, an Alzheimer’s like deterioration in function. The recent attention to the long term effects of other sports related head injuries, especially in professional athletes, stems from this research.

Do Helmets Help

Do helmets protect people from concussions? Helmets do reduce brain damage from trauma in sports like biking and rock climing, but they do it by protecting the skull from fracturing. To dampen the movement of the brain within the skull  – the mechanism of injury in concussion- the diameter of the helmet would have to be so large that it would be impossible to wear.  I have heard many people express surprise about concussions they experienced while wearing helmets in sports like skiing. But if you understand that the skull stops moving in a fall before the brain inside does, you understand that, no, a helmet does not stop a concussion from happening.



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