A concussion causes a temporary disruption in normal brain function due to the brain moving rapidly back and forth inside the skull. This movement can stretch and damage brain cells and create chemical changes that affect how the brain processes information. While usually not visible on standard medical imaging, these internal changes are responsible for the physical and cognitive symptoms experienced after a head impact.
What We’ll Discuss in This Article
- The physical movement of the brain within the skull during an impact.
- How brain cells and connecting fibres are affected by stretching.
- The chemical and metabolic changes that occur after the injury.
- Why standard brain scans often appear normal despite significant symptoms.
- The process of internal healing and the importance of mental rest.
- The risks of sustaining a second injury before the brain has healed.
The Physical Mechanics of Brain Movement
When the head is struck or jolted, the brain, which has the consistency of soft gelatin, slides forcefully against the hard inner walls of the skull. This is often described as a coup-contrecoup injury, where the brain hits one side of the skull and then bounces to hit the opposite side. A concussion is a temporary injury to the brain caused by a bump, blow or jolt to the head.
This sudden acceleration and deceleration do not just move the brain as a whole but also cause rotational forces. These forces can twist and pull the delicate structures within the brain. Because different parts of the brain have different densities, they move at different speeds, which puts significant strain on the connecting tissues and blood vessels.
Changes at the Cellular Level
The primary internal damage in a concussion occurs at the level of the neurons, which are the brain’s communication cells. The rapid movement of the brain can cause the long, thin fibres of these cells, known as axons, to stretch or even tear slightly. This is sometimes referred to as microscopic axonal injury, and it disrupts the electrical signals that allow the brain to function correctly.
When these fibres are stretched, they become less efficient at transmitting information. This is why people with concussions often feel “slow” or have trouble concentrating. While the cells are usually not permanently destroyed, they enter a state of dysfunction where they require significant energy to repair the structural damage and return to their normal state.
The Chemical and Energy Crisis
Immediately following the physical impact, the brain undergoes a complex chemical shift often referred to as a “metabolic crisis.” The stretching of brain cell membranes causes an uncontrolled release of chemicals and ions, such as potassium and calcium. This imbalance forces the brain to work much harder than usual to restore its internal environment.
At the same time, the blood flow to the injured areas of the brain may decrease slightly, meaning the brain is getting less of the oxygen and glucose it needs to fuel this repair work. This gap between the high demand for energy and the reduced supply of fuel is what causes many of the early symptoms like fatigue and headaches. The National Institute for Health and Care Excellence provides detailed clinical guidance on the early management of these head injuries to prevent further complications.
Why Scans Often Appear Normal
It is often confusing for patients when a CT or MRI scan comes back “clear” despite them feeling very unwell. This is because standard medical scans are designed to look for structural damage, such as a fractured skull, a large bruise, or a major bleed on the brain. A concussion is primarily a functional injury, meaning the problem is in how the cells are working rather than a large physical break that a scan can see.
Because the changes are happening at a microscopic and chemical level, they do not show up as a physical mass or a hole on an image. This is why doctors rely heavily on a patient’s symptoms and physical exams to diagnose a concussion. A clear scan is good news because it rules out life-threatening emergencies, but it does not mean that the brain is functioning normally yet.
The Importance of Rest and Recovery
The internal healing process depends heavily on giving the brain the time and energy it needs to resolve the metabolic crisis. Engaging in intense mental activity, such as work or heavy screen use, forces the brain to use up the very energy it needs for repair. This is why “brain rest” is the most important part of early management.
As the chemical balance is restored and the stretched fibres begin to function again, symptoms will naturally start to fade. Most people find that this process takes about seven to ten days, although it can take longer for some. Pushing through symptoms can actually slow down the internal recovery process and make the metabolic imbalance last longer.
Risks of a Second Impact
While the brain is in its vulnerable, energy-depleted state, it is much more susceptible to a second injury. If another jolt occurs before the first concussion has healed, the brain may lose its ability to regulate its own blood flow and pressure. This can lead to rapid and dangerous brain swelling.
This is why “return to play” protocols in the UK are so strict. A person must be completely free of symptoms before they are allowed to return to situations where another head impact might occur. Protecting the brain during this internal “reboot” phase is the best way to ensure there are no long-term cognitive consequences from the injury.
Conclusion
A concussion involves a complex series of physical, cellular, and chemical changes inside the skull. The brain experiences a temporary energy crisis as it works to repair stretched cells and restore chemical balance. Understanding that this is a functional injury helps explain why rest is the most effective treatment and why symptoms can persist even when medical scans appear normal. If you experience severe, sudden, or worsening symptoms, call 999 immediately.
Can a concussion cause permanent brain damage?
Most concussions are temporary and the brain heals fully with rest, but repeated injuries over a long period can increase the risk of long-term cognitive issues.
Why does light hurt my eyes after a concussion?
The chemical changes in the brain can make the areas that process sensory information, like vision and hearing, much more sensitive than usual.
How does the brain “fix” itself?
The brain uses energy to pump ions back into place, repair stretched cell membranes, and gradually restore normal electrical signalling between neurons.
Can I take ibuprofen for a concussion?
In the first 48 hours, paracetamol is usually preferred over ibuprofen or aspirin, as these can theoretically increase the risk of bleeding in more serious injuries.
Is my brain actually bruised during a concussion?
A concussion is usually a functional disruption, but more serious head injuries can involve a “contusion,” which is a physical bruise on the brain tissue.
Why do I feel so tired?
Your brain is using a massive amount of internal energy to restore chemical balance and repair damaged cells, leaving less energy for your normal daily activities.
Does a concussion affect memory?
Yes, the disruption in electrical signals can temporarily interfere with the brain’s ability to create and store new memories or recall recent events.
Authority Snapshot (E-E-A-T Block)
This article explains the internal mechanics of a concussion based on established neuroscientific principles and UK public health guidelines. It has been reviewed by Dr. Stefan Petrov, a UK-trained physician with experience in emergency care and clinical education. The content aligns with the safety standards and diagnostic frameworks provided by the NHS and NICE for managing head trauma in the general public.
