Your skin cells keep dividing, they die and give birth to new cells all the time, even when you're not injured. After an injury, the skin makes a bunch of new cells and uses them to heal your wound. Yet, nerve cells in your brain, also called neurons, do not renew themselves. They do not divide at all. There are very few exceptions to this rule – only two special places in the brain can give birth to new neurons. For the most part though, the brain cannot replenish dead neurons. This is especially worrisome because neurons are very sensitive cells and they die for all sorts of reasons. When you bump your head and suffer a concussion, neurons die. When there is a glitch in the blood supply to the brain, also called a stroke, neurons die. Neurons also die when faced with changes in their own functions, which happens in the so-called neurodegenerative diseases like Parkinson's disease and Alzheimer's disease.
Here is the good news. Because loss of neurons is usually permanent, scientists are working on two important strategies to help the brain after injury. One way is to protect the nervous system immediately after the damage occurs.

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