Nerve fibre interaction with large ganglion cells in the human spiral ganglion. A TEM study.

A TEM study was performed on freshly fixed human spiral ganglions (HSG) biopsied during skull base surgery. Well preserved tissue specimens were obtained for ultrastructural analysis. The investigation revealed that nerve fibres frequently form contacts with the large ganglion cells (type I cells). In the areas of contact, membrane specializations occurred, consisting of symmetric or asymmetric densities often alternating from one cell to the other with a reduced intercellular distance (approximately 10 nm). High power TEM showed the intercellular cleft to contain an extra dense line resulting in a pentalaminar structure. The dense line appeared on the side of the membrane protein concentration. Protein densities jutted into the cytoplasm along the intracellular face spreading into a diffuse cytoplasmic web physically related to accumulating mitochondria. This indicated a concentration of oxygen-dependent metabolic activity in these regions. It is believed that the nerve junctions are involved in electric transmission between type I ganglion cells. The neural junctions were morphologically different from synaptic contacts between small human ganglion cells (type II cells) and nerve fibres which have been suspected of sharing the olivocochlear bundle as their origin.