Electrical activity is essential for brain function. However, neurons, the electrically active cells, are less numerous than the non-electrical glial cells in the central nervous system. The non-electrical components modify the function of neural circuits, depending on the electrical neuronal activity, by wrapping synapses, myelinating axons and phagocytozing the neuronal components. Moreover, recent evidence has suggested that they contribute to neurological and psychiatric disease by regulating neuronal circuits, ultimately affecting their behaviour. In this review, we highlight the physiological functions of glial cells, particularly the electrical activity-dependent processes, to provide further insight into their role in brain function.