Ultrastructural findings of the macaque monkey vestibular ganglion cells

The fine structure of macaque monkey vestibular ganglion cell was studied under the electron microscope. Over 400 serial sections enabled us to observe the entire surface of 114 ganglion cells. Eight ganglion cells were characterized by loose myelin layers. The compact myelin sheath was not demonstrated around any area of the perikaryon in these eight cells. The rest of the cells exhibited both compact and loose myelin layers around one perikaryon. All ganglion cells were bipolar in this study. The initial dendritic process was generally thinner and shorter than the initial axonal process. Both compact and loose myelin sheaths were demonstrated around the initial axonal and dendritic segment as far as the first node of Ranvier, after which all processes became thickly myelinated. This study demonstrated two types of cells: myelinated and unmyelinated. However, there is no obvious size or histological difference between the perikarya of different types of ganglion cells.