The nervous system consists of neurons and glia

The nervous system is made of two major categories of cells: neurons (nerve cells) and glia. A typical neuron has two kinds of neuronal processes (cytoplasmic extensions). A long, thin process called the axon often extends far beyond the cell body (soma). In contrast, the thick, bushy processes called dendrites are usually close to the soma. At the ends of the axons are presynaptic terminals, specialized structures that participate in the transfer of information between neurons; the dendrites of many vertebrate neurons are decorated with small protrusions called dendritic spines, which likewise function in cell-to-cell information transfer. There are many neuronal types with distinct morphologies. Most of them have well-differentiated axons and dendrites, which serve distinct functions.

There are four major types of glia in the vertebrate nervous system: oligodendrocytes, Schwann cells, astrocytes, and microglia. Oligodendrocytes and Schwann cells play analogous functions in the CNS and PNS, respectively. They wrap axons with their cytoplasmic extensions, called myelin sheath, which increase the speed at which information propagates along axons. Oligodendrocytes and myelinated axons constitute the white matter in the CNS (because myelin is rich in lipids and appears white). Astrocytes play many roles in the development and regulation of neuronal communication; they are present in the gray matter of the CNS, which is enriched in neuronal cell bodies, dendrites, axon terminals, and connections between neurons. Microglia are the resident immune cells of the nervous system, which engulf damaged cells and debris, and help reorganize neuronal connections. Invertebrate (e.g. insects) nervous systems have a similar division of labor for different glial types.

protrusion = anything that sticks out from a surface

propagate = spread 

engulf = to surround and cover

division of labor = distribution of functions