Central Myelin.  Myelinated axon. The outer (red arrrow) and inner (blue arrow) cytoplasmic tongues (loops) of the myelin-forming oligodendroglial process are clearly apparent. Axonal microtubules are marked by the small blue arrow, neurofilaments by the red one. Scale = 200 nm. (Human, epitumorous neocortex.)

Central Myelin.  Another myelinated axon (A). M - myelin, O - outer tongue, I - inner tongue. Scale = 60 nm. (Human, epitumorous neocortex.)

Central Myelin.  Pericapillary located oligodendroglia (N - nucleus). The node of Ranvier is marked by the arrow, with the apparent undercoating layer of finely granular dense subplasmalemmal material analogous to that of the axon initial segment. C - lumen of the blood capillary, E - endothelial cell. Scale = 500 nm. (Rat, thalamic ventrobasal nucleus.)

Central Myelin. The myelinated axon (M) branching in the Y-shaped node of Ranvier. Scale = 1 µm. (Rat, lateral geniculate nucleus.)

Central Myelin. The myelin sheath terminates by widened rims of myelin loops and the ensheathed axon (A) becames naked in the region of the node of Ranvier (R). Note intercellular septate-like dark strips between oligodendroglial and axonal plasma membranes in the inset. Scale = 500 nm. (Rat, thalamic ventrobasal nucleus.)