I learned this today. A concussion is a mild traumatic brain injury that temporarily affects brain functioning.
Our brains are protected by cerebrospinal fluid. Cerebrospinal fluid is a colorless fluid that is derived from blood plasma, but it has no protein. It surrounds the brain and acts as a buffer between the brain and the skull, absorbing mild impacts. The cerebrospinal fluid does more than just protect the brain, though. It also clears waste from the brain and it keeps the brain neutrally buoyant. Brains weigh an average of 1.5kg and without the buoyancy provided by the fluid, the weight of the brain would cut off the blood supply to the neurons at the bottom and they would die.
A concussion is caused by anything that transfers forces to the brain that the cerebrospinal fluid can’t cushion against. These forces might be caused by a direct impact or an indirect impact. A direct impact is obviously an impact on the head that transfers forces directly to the brain. This could be a punch or a car accident. An indirect impact is caused by the body suddenly changing position or stopping. In a car accident, the seatbelt could save a person from severe injury, but the whiplash caused by the impact and the seatbelt could transfer forces to the brain and cause an indirect impact. The head moves forward until the seatbelt tightens, stopping the forward movement. The brain continues to move forward and impacts the front of the skull, or rocks back and forth.
These forces can twist the brain horizontally or vertically and this seems to be where the concussion comes from. The twisting puts pressure on the brain stem and stretches the brain cells causing mechanical stress within the brain tissue. The weight of the brain, even though supported by the cerebrospinal fluid, still rests mostly on the brain stem, and puts a lot of pressure on it. The most affected part of the brain is the midbrain and the diencephalon, which are both located at the top of the brain stem and receive the majority of the damage during a concussion. The midbrain is responsible for vision, hearing, motor control, and wakefulness. The diencephalon is a relay center for sensory and motor impulses between the spinal cord and the brain.
Damage to these areas explains a lot of the symptoms that are associated with concussion. After a concussion, there are many different symptoms, but some that are common are: dizziness, nausea, lack of motor coordination, difficulty balancing, blurred vision, ringing in the ears, confusion, disorientation, difficulty paying attention, and amnesia. Not everybody loses consciousness after a concussion, and confusion and loss of balance are far more common. If someone does lose consciousness, it is usually caused by the torque applied in the brain. This is how a knockout punch in boxing works. A strong punch to the jaw at just the right angle will make the head rapidly rotate, faster than the brain inside it can. This leads to twisting, which leads to unconsciousness.
When you are concussed, the twisting brain stretches the neurons and causes chemicals to leak out of the cells. This destabilizes the neurons and hampers their ability to pass signals. A chemical called glutamate that stimulates nerve cells is released in large amounts and it makes neurons fire excessively, creating an imbalance of potassium and calcium. The concussion also causes the blood flow to decrease to the brain. The reason for this is unknown, but it could be to prevent blood loss in case of injury. The decreased blood flow means that the brain is receiving less energy than it normally would. The leaking chemicals damage the mitochondria of some of the cells in the brain, which means they can’t produce much energy. The brain needs lots of energy to heal itself, but it is getting far less than it usually would, so it starts to prioritize its energy, which makes the sufferer extremely tired.
After the concussion, the brain begins to fix itself and it takes a while, but metabolic recovery usually happens over the two weeks after the injury. Most people recover completely from a concussion, but care must be taken during the recovery phase because a second concussion on top of the first can be fatal.
A lot of people suffer concussions every year, but the more concussions you have, the greater the danger becomes. Studies have shown that three or more concussions in a person’s life can increase their risk of developing Alzheimer’s Disease fivefold. An autopsy on the brain of a NFL player showed a build up of tau proteins, which are one of the proteins that are responsible for the disease.
So, a concussion is caused by a direct blow to the skull or something that makes the head move faster than the brain inside it can. This causes twisting, which damages the brain. And this is what I learned today.
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Sources:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC155414/
https://qbi.uq.edu.au/blog/2018/05/what-does-concussion-do-brain
https://www.brainfacts.org/ask-an-expert/what-happens-in-the-brain-during-and-after-a-concussion
https://www.cdc.gov/headsup/basics/concussion_whatis.html
https://www.mayoclinic.org/diseases-conditions/concussion/symptoms-causes/syc-20355594
https://en.wikipedia.org/wiki/Concussion
https://en.wikipedia.org/wiki/Midbrain
https://en.wikipedia.org/wiki/Diencephalon
https://en.wikipedia.org/wiki/Cerebrospinal_fluid
https://www.concussionalliance.org/what-happens-to-your-brain