The answer to this is that exercise stresses the muscles which creates growth factors. This contributes to brand new brain cells and it increases the number of pathways for oxygen, energy, and to remove waste from the brain.
One of these effects is that the immediate effects of exercise are on the neurotransmitters. It causes complex signals to pass through the neurons in the brain. This alerts the brain for learning and makes information easier to retain.
Aerobic exercise is the most beneficial type of exercise on the nervous system. I improves cognition for all people, but the cognition abilities of aerobically active children particularity stand out against those who are not aerobically active.
Hope this helps...sorry for nerding out i love health and science