In the last blog I gave you a general idea of what a concussion is and how it affects us. But have you ever wondered what actually happens to the brain on a cellular level when we hit out head?

DISCLAIMER

These blogs are meant to give you some insight into concussion research and concussion rehabilitation. Concussion research is elaborate, and at times hard to understand. These blogs are meant to simplify the science around concussions, and provide helpful information for you to use whether you are experiencing a concussion, or, know someone who is. This is not a completely comprehensive look at concussions, there is a ton of research out there that we may not touch on. If you are someone who is experiencing a concussion, please seek medical attention. These blogs are meant to support you or a loved one in their concussion journey, not replace seeking individualized help.

Glossary

Pathophysiological: Disordered physiological process due to injury or illness.
Neuron: Another name for a nerve cell that comprise our nervous system.
Dendrites: Top of the neuron. It receives information from neurotransmitters.
Neurotransmitter: How neurons continuously communicate with each other and send messages throughout the body.
Ion: a molecule with a net electric charge due to the loss or gain of an electron(s).
Action Potential: A nerve impulse which causes movement of ions across cell membrane.
Axon: Middle section of the neuron where an action potential is passed.
Sodium Potassium Pump (Na+/K+ Pump): System that maintains resting potential in a neuron. Resting potential consists of maintaining an electrochemical gradient of negative ions on the inside, and positive ions on the outside.
Mitochondria: Powerhouse of the cell! Creates energy for the cell (ATP)

Nerves can vary structurally depending on the responsibility they have in the body (e.g reflex nerves vs. gut nerves). Our bodies are made up of trillions of nerves that help transport information about our actions, thoughts and emotions throughout our body every second, of every day. Cool right? If you have little experience with anatomy and physiology, let me try to explain how our nerves communicate with one another in the simplest way possible. Please refer to picture and glossary.

Our nerves function by maintaining an electrochemical gradient between the inside (intracellular) and outside (extracellular) of the nerve membrane. At resting potential the intracellular membrane has a negative charge, and the extracellular membrane has a positive charge. Once we go to initiate movement, have a thought, or literally ANYTHING, this is what happens..

Dendrites receive information from neurotransmitters, thus opening up ion channels.
Accumulation of positive ions in the membrane create an action potential.
Action potential triggers more ion channels along the axon to open, causing an influx of positive ions into the membrane.
Action potential is continuously transported down the axon through opening of ion channels. Think of it like a wave travelling to shore!
After an action potential has passed each section of the axon, resting potential is restored by efflux of positive ions, and the Na+/K+ Pump. This is known as the refractory period. Another action potential is not able to fire during this time (lasts for roughly one millisecond).
Action potential reaches synapse terminals where more neurotransmitters are released to dendrites of another neuron.
REPEAT.

Neurotransmitters are the body's chemical messengers. They act as the communication line from one neuron to the other, ensuring messages are appropriately transported throughout the body. Neurotransmitters can be classified as excitatory or inhibitory. Excitatory neurotransmitters (e.g. norepinephrine) increase the likelihood an action potential will occur. Inhibitory neurotransmitters (e.g. GABA), decrease the likelihood of an action potential to occur. Which makes sense! It's in the name!

The Na+/K+ Pump is a protein embedded in our cell membranes that regulates the neuron's resting potential. The pump works to transport three Na+ from the intracellular membrane to extracellular membrane, and two K+ from the extracellular membrane to the intracellular membrane. Thus, more positive ions travel out, keeping the inside of the membrane more negative.

Like any functioning pump, it needs a source of energy in order to work. Introducing, ATP! The body's energy source derived from the breakdown of glucose. When phosphorus (P of ATP) binds to the pump, it changes the opening of the protein from the intracellular to the extracellular membrane. This is how Na+ and K+ travel over the membrane. Note, most ions need support, like a pump or a channel, to travel over the membrane. While the Na+/K+ Pump is powered by ATP, some pumps or channels are powered by voltage. Thus, when an action potential travels down an axon, some channels will open or close due to the change of the electrochemical gradient of the membrane.

Okay, that could've been a lot of new information! But stick with me here. Now that you've gained some key knowledge (hopefully) of how our nerves are meant to function, we can now relate it to what happens when we suffer a concussion.

I would like everyone to imagine the scene from the office when Dwight is conducting a fire safety drill (If you don't know what I am referring to, for one, SHAME ON YOU. Two, here is a clip to give you an idea.

This is what happens when our brain hits our skull. DYSFUNCTION AND STRESS. Our nerves go through microstructural damage by sheering or stretching. What does it mean to stretch a nerve? Disruption to blood flow, ion channels, and neurotransmitters. All those important elements we just talked about that help us function.

Disruption of Blood Flow

When blood vessels are broken or damaged, the brain is not supplied with adequate blood flow. If we have a reduction of blood flow, it means we have a reduction of oxygen being transported to the brain. Lack of oxygen leads dysfunction and takes longer for us to heal since oxygen is a key element to promote healing.

Disruption of Neurotransmitters

When nerves are initially damaged, there tends to be a massive release of excitatory neurotransmitters, like glutamine. The release of glutamine triggers the influx of positive ions from the extracellular membrane, like Na+ and Ca+ ions. Why is this bad? Increase in glutamine, influx of Ca+ and Na+ moving into the intracellular membrane which directly affects the function of the Na+/K+ pump and restoring resting potential. Remember, another action potential will not be able to fire if the neuron does not stabilize by cycling through its refractory period. On a bigger scale, this means there will be delayed or lost messages from the brain or body. Furthermore, the accumulation of Ca+ can impair ATP production in the mitochondria* and can lead to cell death.

Disruption of Na+/K+ Pump

We spoke about the importance of the Na+/K+ pump in regards to maintaining resting potential in neurons. With the influx of positive ions in the membrane, the Na+/K+ pump is working overtime to try and restore resting potential. We know that ATP powers the pump. Thus, if the pump is working harder, ATP supply needs to be greater. Our body does everything it possibly can to try and supply these pumps with energy, however the supply has trouble keeping up with the demand (mitochondria dysfunction) which leads to an energy crisis. Ever wonder why you are super fatigued all the time after the initial concussion? A lot of our energy is going towards stabilizing and fixing our dysfunctional neurons and vessels.

All these changes happen within seconds, but can last up to weeks or months to recover. For example, the massive influx of excitatory neurotransmitters stabilizes within minutes, but proper blood flow is usually not restored until 10-14 days after the initial blow. That's why it's so important to start aerobic rehab within a few days of hitting your head. It promotes healing of damaged blood vessels and leads to the creation of others to restore proper blood flow to the brain.

This also brings into perspective how you need to have a structured plan to return to sport or work after the initial hit. Even if you feel 'fine' within a few days, the body needs time for the metabolic changes to subside. Going back to 'normal' too soon, can delay the recovery time and make symptoms worse. Furthermore, it can also lead to Post Concussion Syndrome, the very scary reality that your symptoms become chronic.

Everyone's recovery time looks different. Children, adults, people with predisposed health conditions will all experience a concussion differently. Why? Because brains are complicated. So it's important to find concussion rehab help right away, be patient, and listen to your body. If you are in a position to start rehab within the first 48-72 hours, do it! It is crucial to kickstart recovery and increase your chances of improving symptoms quicker.

References

Crash Course (2014). The Chemical Mind: Crash Course Psychology #3. [Video]. YouTube. https://www.youtube.com/watch?v=W4N-7AlzK7s

Giza, C. C., & Hovda, D. A. (2001). The Neurometabolic Cascade of Concussion. Journal of athletic training, 36(3), 228–235.

Sahyouni, R., Gutierrez, P., Gold, E., Robertson, R. T., & Cummings, B. J. (2017). Effects of concussion on the blood-brain barrier in humans and rodents. Journal of concussion, 1, 10.1177/2059700216684518. https://doi.org/10.1177/2059700216684518

Speed Pharmacology (2016). Neuron Action Potential (Made Easy). [Video] YouTube. https://www.youtube.com/watch?v=XnksofQN8_s

Rehab Lab (2022, March 7). Day 1 Concussion Recovery Bootcamp. [Video] YouTube. https://www.youtube.com/watch?v=gOxNefEGUv8