Robert Smith, age 9, of Trumbull, Connecticut, for his question:
What exactly is a nerve?
When you stub your big toe, chances are you yelp "OUCH!" faster than you can blink. This happens because a team of fine threads reported the crash and flashed back a pain signal. One thread was the longest nerve in your body. It reaches all the way from your big toe to the bottom end of your backbone: A team of other nerves helped to relay the report to headquarters and bring back the OUCH signal. And the network of nerves did all this before you had time to think.
Nerves are living cells that scientists call neurons. You have at least ZO billion of them and your body could not possibly get along without them. They are embedded in the skin and flesh, the bones and muscles and in all the inside organs. These nerve cells come in different shapes and sizes because each has a special duty. Most of them are more or less linked together in teams to relay news events to the brain and flash back orders.
Most nerve cells are shaped like miniature kites with long skinny strings. Some of the kites have several pointed corners that spread out branches of skinny fingers. The long skinny tail of a kite may end in a tufted brush of skinny little fingers. The branching threads on other nerve types are short or medium long. Another type has a miniature bulb at the end of its very long, very thin thread. The shape of a nerve cell helps it to do its special duties. Nerves in your legs attend to leg messages, to and fro, nerves in your hands attend to hand messages and so on:
All these 10 billion or so nerves are linked together in the orderly nervous system. The zillions of bits of news they gather are sent to headquarters: This may be the brain in your skull or the spinal cord inside your backbone. The brain is a brilliant computer made entirely of special nerve cells. They are stationed in groups to cope with messages from this or that part of the body and there are special centers to compare the news from all over. Nerves flash endless little news items and the teams of brain cells cope with them in a jiffy. They sort, compare, decide what to do and flash sensible orders to this or that part of the body. They do a lot of this work without bothering you to make you think about it.
When you stub a toe, sensory nerves flash the news to headquarters and motor nerves flash back the pain signal. There are sensitive sensory nerves in every patch of skin. Their skinny fingers know when you touch something hot or cold, rough or smooth, wet, dry or sticky. Other nerves in the team help to relay these news items to headquarters. The brain relays its orders back through teams of motor nerves.. Their skinny fingers prod muscles and other parts of the body to carry out the orders. Special in between nerves help to shuttle signals across gaps in the relay system.
All the nerves work together like a super duper miniature telephone system. A telephone uses electric power to flash signals through wires. A nerve also flashes electric signals. Its little kite is the cell body that uses food to keep it in working order. Moist chemicals in the surrounding cells provide the electricity.. The nerve fibers flash the signals along to and fro, faster than you can blink.