Michael Cooley, age 12, of Indianapolis, Indiana, for his question:

What exactly are neurons?

Without a network of neurons, the human body would be a mindless, disorganized blob. These highly specialized cells of the nervous system organize the body's functions and give meaning to its life. The neurons are its sensors and signals, its computers and cables of communication.

Twang a guitar string. The motion triggers pulsing vibrations as your muscle energy is translated into sound energy. This can be compared with certain activities of the nerve cells, alias the neurons, inside the body. A comparison of this sort is an analogy, and like most analogies it takes you only part way toward grasping a new problem. A neuron is a living cell, a guitar string is inanimate. Sound is triggered by vibrating molecules and it travels about 1,100 feet per second. Neurons are powered by electrochemical energy and they carry their impulses at about 350 feet per second. This speed, however, is fast enough to flash a signal from your finger to your brain and back again in 1/100th part of a second.

The nervous system is a miraculous network of some 10 billion assorted neurons. Each is a living cell with a small central nucleus that governs its chemical processes and organizes its specialized duties. Unlike most living cells, the cytoplasm around the nucleus of a nerve cell spreads out into threads and fringes of sensitive fingers. These dendrites or nerve endings are sensors waiting to be triggered by stimuli coming from outside the body or from other neurons or stimuli inside the body. The neuron network is in touch with every corner of the body. Each of its cells is triggered to respond to certain stimuli and to perform a specialized duty in the well organized nervous system.

Sensitive dendrites are on guard in every spot of the skin. They are the endings of long cable type sensory nerves that are sheathed in layers of special tissue. They respond to stimuli of heat and cold, wet and dry, rough and smooth. As soon as a stimulus is received, the neurons spring into fast action. In the long cable of a sensory neuron, electrochemical energy sends an impulse on its way to the brain. The cable may be a foot or more long and the impulse is flashed to the next neuron in a relay system.

In less time that it takes to tell, the signal is relayed to the spinal cord and the correct department of the brain. There it is evaluated by teams of other neurons and the proper instructions flashed back to relays of motor neurons. These are the cable type neurons that carry messages from the brain to the muscles. Before you know it, you are ready for action. The long sensory and motor neurons form the communication system between the brain and all parts of the body. The brain and spinal cord are made of tiny neurons, most of them shaped like cones or triangles.

Past automatic action is triggered by data already built into the brain and spinal cord. Decisions are made in the higher, cerebrum part of the brain. A man made computer decides on the basis of the data programmed into it, and so does the brain. A pre student can strum a note on a guitar    but maybe not the one he wants. After a few lessons, skills are programmed into his brain computer. His neurons learn to respond with the right relays to twang the right notes and chords to sound off the right song.