In which process does a portion of the cell membrane fold inward and surround molecules to bring them into the cell?

Na+ loss through sweet plus the dilution has lowered na+ concentration outside of neurons, altering the na+ equilibrium potential. sodium exists more outside the cells than inside. when na+ is lost by sweat plus the dilution( because they drink a lot of water) changes the concentration outside the cell, forcing the water to enter the cell and attempt to balance the concentration inside/outside.the problem is that the abundance of water will cause the cells to swell. most cells can adapt, however, the brain cells can't that's why the runner has confusion and can't control the muscles.  if not treated and this occurs in less than 48 hours, it can be immediately fatal .

the correct answer is: " ventricles " .

"recent advances in brain imaging have allowed clinicians to make scientifically useful comparisons in the relative size of the chambers in the brain that are filled with cerebrospinal fluid."

{source: refer to text within question.}.

these chambers are called ventricles .