When the head is subjected to a shock force, such as a collision or an impact from a foreign object, the fluid membrane that surrounds the brain is unable to sufficiently keep the brain from colliding with the skull. When the brain has this collision with the skull, it causes brain cells to be violently disfigured, releasing potassium and glutamate from the cell. Both potassium and glutamate are necessary for normal brain function, and without them, brain cells constrict and fill with calcium. Once constricted, these brain cells are no longer able to effectively send messages to each other, an effect that spreads throughout the brain as more and more cells are unable to communicate. This inability for the brain to send out signals leads to the generally understood first symptoms of a concussion: a lack of awareness, erratic activity, memory loss, and in the most extreme cases, unconsciousness. The lasting effects of a concussion manifest long after these first symptoms, however. The body attempts to increase the supply of potassium to the brain by burning glucose, and in doing so allows lactic acid to build up in the brain, which reduces blood flow (and therefore reduces the ability of the brain to function properly), for up to four weeks after the concussion occurs. In addition, many brain cells have had too much exposure to too much calcium, leading to brain cell death. With repeated exposure to concussions, this brain cell death can manifest itself in serious, irreversible brain conditions such as CTE.
Though concussions are mostly a chemical reaction to trauma in the brain, they are still caused by physical stimuli. That’s why preventative measures, such as wearing helmets and learning proper checking techniques are so important to the game of hockey.
Mark E. Halstead, Kevin D. Walter, The Council on Sports Medicine and Fitness
Pediatrics Sep 2010, 126 (3) 597-615; DOI: 10.1542/peds.2010-2005
Izraelski, Jason. “Concussions in the NHL: A Narrative Review of the Literature.” The Journal of the Canadian Chiropractic Association 58.4 (2014): 346–352. Print.