ABSTRACT
The human brain contains something on the order of ten billion neurons. Neurons are unlike nearly every other type of cell found in the human body in that they do not usually reproduce themselves. The typical neuron consists of a central cell body a few thousandths of an inch across. Its principal fiber, called the axon, usually one of the longest, carries outgoing information from the cell body to other neurons. Neurons vary widely from one part of the brain to another. Some have hundreds of dendrites on them, some have only few. In some the fibers are only a millimeter or less in length; in others they may be up to two feet in length, stretching from the brain to the base of the spinal cord. Some make tens of thousands of connections with other neurons; some one or two. Yet despite such wide variations, their basic structure is generally the same.
