Compare the rates of cell division occurring in your neurons and your hair follicles.

Once you finish growing to adulthood, neurons stop dividing. Hair follicle cells constantly divide throughout your lifetime since they are constantly producing cells that become part of the hair itself as they die. So in an adult, the rate of cell division for neurons is zero (although there is some counter-evidence but it is certainly very low) while the hair follicle rate is much higher on the order of once every few days or faster.