Neurons

Neurons are formed by dendrites, structures that receive information from other neurons or sensory receptors, cell body, region where metabolic reaction happens and nucleus is found, axon, longest part of the cell, take the information away from the cell body and lead to the axon terminal, region of transmitting information.

Some neurons have their axons surrounded by a special layer of glial cells called Schawann cells, these layers are called Myelin Sheath. The space between Myelin Sheath are called node of Ranvier. Myelin sheath will nourish and protect the neuron, as well will speed up the nervous impulse transmission.
Myelinated neurons ( neurons that have myelin sheath) are known to compose the white matter, while Unmyelinated neurons form the grey  matter.