What Is a Concussion? Understanding What Happens to Your Brain
Most people understand that a concussion happens when the brain is affected by a force or rapid movement.
But that doesn't really explain what a concussion actually is.
Why can a relatively short impact cause headaches, dizziness, brain fog, fatigue, visual problems, exercise intolerance, and sleep changes?
And why can you feel terrible even when your CT or MRI looks completely normal?
To understand concussion, it helps to look beyond the impact itself and understand what happens inside the brain afterward.
What Is a Concussion?
A concussion is a type of traumatic brain injury that causes a temporary disruption in normal brain function.
The force of the injury causes the brain to move rapidly within the skull. That movement can stretch and disrupt the membranes of brain cells and trigger a complex series of chemical and metabolic changes.
This series of changes is called the neurometabolic cascade of concussion.
In simple terms, the brain's normal balance gets disrupted, and the brain has to use a tremendous amount of energy trying to restore that balance.
And this is where the concept of a concussion energy crisis comes in.
What Happens Inside Your Brain During a Concussion?
Think of your brain as a highly sophisticated electrical and chemical system.
Billions of brain cells communicate with each other by carefully controlling electrical signals and the movement of chemicals and ions across their cell membranes.
A concussion suddenly disrupts that balance.
The initial force can cause brain cells to release large amounts of neurotransmitters and cause ions such as sodium, potassium, and calcium to move across cell membranes.
The brain then has to work hard to restore its normal balance.
That takes energy. A lot of energy.
At the same time, changes in blood flow and cellular metabolism can make it more difficult for the brain to produce and deliver the energy it needs.
This creates a mismatch:
The brain's demand for energy increases while its ability to meet that demand is disrupted.
This is commonly described as the neurometabolic energy crisis of concussion.
What Is the Neurometabolic Cascade?
The word cascade sounds complicated, but the basic idea is actually pretty simple.
One change leads to another.
After the initial injury:
The brain cells are disrupted.
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Chemical and electrical activity changes.
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The brain uses additional energy to restore its normal balance.
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Energy demand increases.
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Changes in blood flow and cellular metabolism can interfere with the brain's ability to meet that demand.
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The brain enters a period of altered metabolism and function.
This entire process is referred to as the neurometabolic cascade.
The important thing to understand is that the concussion isn't simply the moment your head was hit.
That impact can trigger a series of changes that continue after the initial injury.
Why Is a Concussion Called an "Energy Crisis"?
Your brain is extremely energy-hungry.
Even though the brain makes up only a small percentage of your body's weight, it requires a significant amount of energy to maintain normal function.
After a concussion, the brain's energy demands can temporarily increase while its ability to produce and use energy efficiently is disrupted.
A simple analogy is this:
Imagine your house suddenly has a huge increase in electricity demand at the exact moment your power supply becomes less efficient.
The house still has to function.
The lights still need to work.
The refrigerator still needs power.
But the system has a harder time meeting the demand.
That's essentially the concept behind thebrain's energy crisis after concussion.
This is also one reason activities that were previously easy—like reading, using a computer, exercising, or concentrating—can suddenly feel much harder.
Why Does a Concussion Cause So Many Different Symptoms?
Your brain controls or coordinates an enormous number of functions.
So when brain function is disrupted, the symptoms can be surprisingly varied.
You might experience:
Physical symptoms
Headache
Dizziness
Nausea
Fatigue
Balance problems
Sensitivity to light or sound
Cognitive symptoms
Brain fog
Difficulty concentrating
Memory problems
Slower thinking
Mental fatigue
Visual symptoms
Blurred vision
Difficulty focusing
Eye strain
Difficulty tolerating visually busy environments
Autonomic symptoms
Exercise intolerance
Rapid heart rate with activity
Dizziness when standing
Unusual fatigue
Sleep symptoms
Difficulty falling asleep
Sleeping more or less than usual
Feeling unrefreshed after sleep
You don't have to experience all of these.
And two people can have completely different symptoms after a concussion.
That doesn't mean one person has a "real" concussion and the other doesn't.
It means that the brain systems affected—and the way each person's brain and body respond—can be different.
Why Doesn't a Concussion Always Show Up on a CT or MRI?
This is one of the most confusing things about concussion.
You can have significant concussion symptoms while having a completely normal CT scan or conventional MRI.
That's because many of the changes associated with concussion occur at the cellular, chemical, metabolic, and functional level rather than as a large structural injury that can be seen on routine imaging.
So a normal scan doesn't mean:
"Nothing happened."
It means that the type of changes occurring with a concussion may not be visible on conventional imaging.
Why Do Some People Continue to Have Symptoms?
For many people, concussion symptoms improve relatively quickly.
For others, symptoms persist.
When symptoms continue, the picture can become more complicated than the initial neurometabolic changes.
Different systems can contribute to persistent symptoms, including:
The vestibular system
The visual system
The autonomic nervous system
The neck and cervical spine
Exercise regulation
Sleep
Headache mechanisms
Cognitive demands
And sometimes several systems are contributing at the same time.
This is why persistent concussion symptoms aren't necessarily something you should simply "wait out."
The important question becomes:
What is contributing to the symptoms, and what can be done about it?
Can You Do Something to Help Your Recovery?
Yes.
Understanding what happens during a concussion is important—but it's only the beginning.
There are many things you can do to support recovery, including appropriately progressing physical activity, addressing sleep and nutrition, gradually rebuilding tolerance to normal activities, and identifying specific systems that may be contributing to persistent symptoms.
Want practical concussion recovery tips you can use at home?
Concussion Recovery Tips You Can Do at Home
A More Structured Approach to Concussion Recovery
If you're still struggling with concussion symptoms and want a more structured approach to recovery, The Concussion Solution was created to help you work through the different systems that can contribute to persistent symptoms.
Looking for In-Person Concussion Care in Park City, UT?
If you live in the Park City area and would prefer one-on-one, in-person concussion physical therapy, Happy Brain Physical Therapy offers individualized concussion care in Park City, Utah.
Frequently Asked Questions About Concussions
What is a concussion in simple terms?
A concussion is a traumatic brain injury that temporarily disrupts normal brain function. The initial force can trigger a series of chemical, electrical, and metabolic changes in the brain known as the neurometabolic cascade.
What is the concussion energy crisis?
After a concussion, brain cells require increased energy to restore their normal chemical and electrical balance. At the same time, changes in blood flow and cellular metabolism can interfere with the brain's ability to meet that increased demand. This mismatch is often described as the concussion energy crisis.
What is the neurometabolic cascade of concussion?
The neurometabolic cascade is the series of changes that can occur in the brain following a concussion. These include changes in neurotransmitters, ion movement, energy metabolism, blood flow, and cellular function.
Can you have a concussion with a normal CT scan?
Yes. Conventional CT and MRI scans can be normal following a concussion because many of the changes occur at the cellular and metabolic level rather than as an obvious structural abnormality.
Why does a concussion cause brain fog?
The changes in brain-cell function, neurotransmission, and energy metabolism that occur after concussion can affect cognitive processes such as attention, memory, and processing speed.
Why can exercise make concussion symptoms worse?
Exercise increases the body's and brain's demand for energy and requires the cardiovascular and autonomic systems to respond appropriately. When these systems aren't tolerating activity normally, exercise can temporarily increase symptoms.
Related Concussion Articles
Concussion Recovery Tips You Can Do at Home Practical things you can do to support your recovery.
Why Do I Still Have Concussion Symptoms Months Later? Why symptoms can persist and what may be contributing to them.
Why Does Exercise Make My Concussion Symptoms Worse? Understanding exercise intolerance after concussion.
Post-Concussion Autonomic Dysfunction: Symptoms, Causes & What Helps How autonomic dysfunction can contribute to persistent symptoms.
Why Am I Dizzy After a Concussion? Understanding possible vestibular, visual, neck-related, and autonomic contributors to dizziness.
Screen Time After a Concussion: How Much Is Too Much? How to gradually rebuild tolerance to screens.
Looking for More Guidance With Your Concussion Recovery?
If you're still experiencing symptoms and aren't sure what to do next, The Concussion Solution provides a structured approach to help you understand your symptoms and work through your recovery from home.
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