Why is playing sports with concussion symptoms so risky?
During a concussion, arteries constrict, slowing blood flow to the brain. At the same time, calcium floods the energy-producing portions of brain cells. That calcium plays a mean defense, blocking oxygen- and glucose-rich blood from replenishing neurons' energy supply. Brain cells get sluggish, and a concussed athlete who can't focus or suffers from slower reaction times is left more susceptible to a slew of other injuries, including another concussion. A second blow to the head could lead to more arterial constriction and more calcium infusions.