What happens if nerve cells are damaged or destroyed?

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All the nerve cells you can ever have are present at birth. Once a nerve cell dies, it cannot be replaced. There is no reason to worry, however. There is a very large stock of nerve cells, so that an individual will have more than enough to last a lifetime. Even though the cells body cannot be replaced, some extensions have the ability to grow back after an injury. This is why some reattached limbs can regain some of their functions.