Central nervous system
The central nervous system consists of neuronal and non-neuronal cells.
The neuronal cells are the Unipolar cells, which are the somatosensory neuronal cells; pseudo-unipolar cells such as in the dorsal root ganglion; bipolar cells, which are all first-order neurons (primary special sensory cells), and multipolar cells such as those in the brain.
The non-neuronal cells include the microglia, which act as the macrophages of the nervous system; oligodendrocytes, which provide myelin to CNS neurons; Schwann cells, which provide myelination for the peripheral nervous system; and fibrous or protoplasmic astrocytes, which provide structural support to nervous tissue and act as "guide wires" during development that direct neuronal migration. Astrocytes also aid in repairing damaged neural tissues, and contribute to the formation of the blood-brain barrier, acting as regulators of electrolyte balance by buffering potassium ions (and others) in the extracellular space.