They are collections of granular endoplasmic reticulum. Ordinarily, a neuron has several dendrites and a single axon. Special methods are required to show the geometry and spatial relationships of neurons. Also, a significant decrease in the number of spines has been reported in the brains of elderly people. Consequently, there is considerable interest in learning what happens to these structures in aging individuals.
Axons conduct nerve impulses between neurons.
The rate of this conduction varies with the diameter of the axon and thickness of the myelin sheath. The greater the diameter and the thicker the myelin sheath, the faster the rate of conduction. Obviously, the fewer the nodes, the faster the rate of conduction. However, not all axons have a myelin sheath. These are called unmyelinated axons.