Glycogen is a brilliantly designed glucose storage molecule. While we understand quite precisely how glycogen functions in liver and muscle, this remains an emerging story for glycogen in the nervous system. In fact, the very existence of glycogen in normal peripheral nerve was only recently established. We have studied the physiology and functions of glycogen in CNS white matter and peripheral nerve, using acutely isolated mouse optic nerve (MON), a typical CNS white matter tract, and mouse sciatic nerve (MSN). These advantageous preparations allowed rigorously experimental assessment with quantitative electrophysiological techniques, including an ‘enzyme’ electrode for detecting lactate, biochemical glycogen assay and direct EM visualization of cytoplasmic glycogen particles.