WHAT IS A CONCUSSION?

LEARNING ABOUT WHAT A CONCUSSION IS AND THE RISK FACTORS ASSOCIATED WITH IT.

The best explanation I have heard to define a concussion is to describe it as an acceleration and deceleration injury to the brain.  Instead of thinking of a concussion as simply a bruise on the brain, it’s now understood as damage to the brain's delicate nerve fibers (neurons), which can stretch and be disrupted under shearing and rotational forces. This triggers a chain reaction of changes that the nervous system works to fix.

The brain is maintained through the nervous system, both the sympathetic and parasympathetic nervous system help to guide physiology in the brain & providing it with the appropriate neurotransmitters and blood flow to function. Neurotransmitters are chemical messengers that help the brain communicate and function properly. When there is a disruption to these processes the brain and nervous system must work overtime to correct it on top of regular daily function. In addition to these changes, we see a diminished level of cerebral blood flow (blood flow into and within the brain) which means the brain receives less oxygen and fewer nutrients, which it needs to heal and function.

We are about to learn about the neurophysiology of the brain after a concussion – so buckle up!

Understanding of how ions operate within the brain have been heavily researched and demonstrated through the schematic below.  Ions are tiny, charged particles, like calcium and potassium, that play a key role in how brain cells send signals and maintain balance. We can see that at the point of injury and for several hours, there are extreme changes that occur in the brain as a response to the neuronal changes, and while most of those ions return to their baseline, calcium ions stay high for 3-4 days, and cerebral blood flow operates at a lower threshold for up to 10 days.

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Think of brain cells as tightly controlled balloons. During a concussion, the structures controlling ion-flow become thinner, causing the cells to leak particles like potassium while taking in excess calcium, disrupting their balance. This causes a depletion of energy stores (ATP) and an increase of glutamate release. Glutamate is a chemical that helps brain cells communicate, but too much of it can cause an overload of calcium in the cells.

This overload damages the energy-producing parts of the cell (the mitochondria), making it even harder for the brain to recover. This means the brain is working extra hard to restore balance, but it doesn't have enough blood flow to supply the energy it needs.

For about 20% of people, concussion symptoms persist beyond 10-14 days, resulting in post-concussion syndrome (PCS). This means the brain takes more time to heal and symptoms can persist for weeks, months, or even years. The largest risk factors for not recovering from an acute concussion are:

• History of concussions

• Being female

• Having a high symptom load (multiple symptoms instead of just one or two)

• A history of anxiety or depression may slow recovery because the brain is already managing stress, making healing more difficult.

Once a patient enters PCS, the outcomes vary in time and level of return.  Some patients if managed correctly can resume all their activities within 6 weeks, some take months or even years to recover. 

New research by Chou T-Y et al. (2023), demonstrates longer lasting symptoms of a concussion can translate into higher rates of ankle sprains and ACL-injury.  In this latest systematic review, of 27 studies with over 1500 participants, they compared concussion to non-concussion athletes, in their risk for lateral ankle sprain and ACL-injury.  The study found that after a concussion, people often struggle with balance and slower movements, increasing their risk of injuries like ankle sprains or ACL tears. The time frame that this occurs ranges from 2-days to 34-months for an ankle sprain and 60 days following sport resumption to 6.5 years for an ACL-injury.

Remember, during concussion recovery, the brain works harder but has less blood flow, making it harder to perform even simple tasks. For example, when you look at an image on your phone or computer, your brain must process all the details like colors, shapes, and shadows to make sense of it. For a healthy brain, this is automatic. But for a concussed brain, it’s like trying to solve a puzzle while someone is shouting questions at you, and the lights flickering on and off—it quickly becomes overwhelming.

For these reasons, it’s crucial to seek guidance from a specialist in concussion rehabilitation after a concussion. You want to make sure that you have appropriate guidance through the first two weeks after the concussion to help prevent the occurrence of entering PCS.

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References: 

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Chou T-Y, Huang Y-L, Leung W, et al. Br J Sports Med 2023;57:1509–1515. doi:10.1136/bjsports-2023-106980

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Christopher C. Giza; David A. Hovda. The Neurometabolic Cascade of Concussion. Journal of Athletic Training 2001;36(3):228–235

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