Concussions are difficult to spot and treat without an obvious injury to the brain. A brain scan will not show bleeding or large-scale damage. But concussions can cause serious injury to the brain at the cellular level.
Ion leaking is one dramatic example of the effects of concussion on the brain. The impact of a concussion tears tiny holes in the membranes of neurons. Ions, because they are only single atoms, are able to uncontrollably flow in and out of the cell through these tears. Neurons use sodium ions to carry electrical signals. They take in sodium at exactly the right time to create an action potential. When sodium rushes in all at once, neurons become stuck in an inactive state. Ion flux may explain the migraine symptoms that can come with concussion. Similar movement of ions occurs in migraines, and people with a history of migraines are more likely to have worse concussion symptoms.
A concussion can send the brain into an energy crisis. Moving ions in and out of cells costs a lot of energy, even for a healthy brain, because it takes energy to run the tiny pumps that transport the ions. After a concussion, the brain needs even more energy. The brain works extremely hard to restore the balance of ions. Since blood flow to the brain is reduced after a concussion, the low supply of energy makes the high demand worse. Energy crisis probably explains why getting a concussion makes the brain more sensitive to a second concussion. Research has shown that if a second concussion happens after glucose metabolism rises back to normal, the two concussions act as separate small injuries instead of one massive injury.
The stretching forces of a traumatic brain injury are known to damage axons in the brain. Axons are the long, thin parts of neurons that carry signals, kind of like wires. It makes sense that these delicate structures are especially vulnerable to concussion. When the brain bounces against the skull, axons can partially tear or completely disconnect from neurons. Myelin, the fatty insulating layer on axons, gives some protection against concussions. That might explain why young children are more vulnerable, since the process of making myelin happens early in life. Axon injury is probably an important factor in the slowed thinking that comes with concussion.
Some of the more subtle signs of concussion, such as migraine or mental fogginess, might be too slight for someone to know that their brain is seriously injured. As we learn more about the causes of concussion symptoms, hopefully we will be able to develop accurate tests for concussions.
What Does Concussion Do to Our Neurons?
