Nerve cells (neurons) and glial cells are the primary cellular components of the nervous system. Neurochemical signaling is predominantly carried out through a complex series of physiological connections between adjoining neurons. Glial cells participate in a constellation of functions that are vital for proper brain function. Their historically appreciated contribution to neuronal function has expanded to include recognition of their role in regulating the content of the extracellular space and regulation of neurotransmitters at the synaptic junction.