However, most people would gladly trade them in for a new set of hair cells. Each inner ear has 30,000 hair cells, so called because of the hair-like structures that protrude from the top of each cell. These cells are completely formed before birth and are not replaced spontaneously in humans or any other mammals. The outer hair cells are micro-motors that amplify the incoming sound waves. The inner hair cells detect these waves and trigger nerve impulses to the brain where hearing occurs.
Hair cells are very sensitive, but they are also very fragile.
Loud noise, aging, toxic medications, trauma, and genetic conditions all may destroy hair cells and cause hearing loss. Without the outer hair cell amplifier, speech sounds become too faint to understand. When the inner hair cells are damaged, clarity is lost, no matter how loud we make the incoming signal. Over the past decade, regrowth of certain human cells has become a reality. For example, new skin can be grown in the laboratory and used to resurface large burns.