If the cell body of a neuron is destroyed, that neuron can not be replaced. Mature neurons are incapable of cell division. 16.2 Neurons have a main CELL BODY, which is 5-140 micrometers in diameter. The cell body contains the nucleus, mitochondria and other cellular organelles. The AXON is a single long, thin process that conducts nerve impulses AWAY from the cell body to another neuron, muscle cell or gland cell.
Axons vary in length from a few millimeters to a meter or more.
There can be 10,000 or more axon terminals per neuron. In some neurons, both the axon and dendrite are nerve fibers. The myelin sheath protects and insulates the nerve fibers from one another, and it increases the speed of transmission of nerve impulses. Myelinated fibers conduct nerve impulses more rapidly than unmyelinated fibers. Myelin sheaths are produced by specialized neuroglia.