Cheryl Kay Finer, age 11, of Utica, New York, for her question:
How can hair and nails grow without nerves?
When living tissues are damaged, sensitive nerves inform the brain and the brain flashes pain protests to the conscious mind. Yet nails can be cut and hair can be trimmed with no protests whatever. Obviously these items have no nerves to relay local conditions to the brain. They are non living tissues and non living things are not expected to grow. Yet we know for a fact that hair and nails continue to grow longer, week by mysterious week.
The mystery here is behind the scenes, hidden deep within certain specialized pockets of skin. Nothing goes on in the epidermis, the papery thin surface layer of the skin. It is made of worn out cells that flake off continuously, especially when the skin is washed. This causes no pain because the epidermis is made of dead cells serviced by neither nerves nor blood vessels.
But down in the deeper layers of skin, things are very different indeed. These tissues are alive, nourished by numerous mini blood vessels and riddled with networks of sensitive little nerves. When these living tissues are injured, the nerves inform the brain and the brain signals protests of pain.
These lower skin levels contain quite an assortment of special centers. There are glands that manufacture oils and ooze them out to keep the surface skin soft and pliable. There are sweat glands that manufacture and ooze beads of salty perspiration. When this moisture evaporates, it uses up heat and cools off the surface of the skin. At least, that is what body perspiration is supposed to do.
Also buried down in the skin there are 20 little nail building factories and numerous mini hair building factories. These remarkable centers build cells and more cells to keep the hair and nails growing. They are built within living tissues, which are fed by fine blood vessels and protected by numerous nerves.
The root of the average fingernail is hidden where the little white half moon tunnels below the skin. It is called the matrix and in its own mysterious way it extracts special chemicals to build cells with extra tough walls. Actually these bio-chemicals are similar to the horns, hooves and claws of the animal kingdom.
As the matrix builds more and more of these cells, older cells are pushed forward and the nail grows toward the tip. The pale half moon at the base of the nail is a region of smaller and diminishing nerves and blood vessels which are absent in the rest of the nail.
Each hair on your head grows from its own private root of living tissue, which is buried deep in the skin of the scalp. It, too, extracts horny chemicals to build firm walled cells. Here, too, the older cells are pushed farther out as new ones are added below.
Hair and nails are durable, non living cells without nerves or blood vessels. But they were built by special centers of living tissue. When a matrix is inured very seriously, the future nail may be deformed or fail to grow altogether. And sometimes hair roots wither away and a person becomes bald.