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Abstract

A three-dimensional model of the cell membrane contact area was made between two large spiral ganglion cells (type 1 cells) from a cell cluster in a normal human cochlea. The freshly fixed cochlea had been removed during skull base surgery, processed, and sectioned for ultrastructural analysis. 400 consecutive serial thin sections were prepared from the apical portion where the nerve cell density is high and cell clusters are numerous. A cell cluster is defined as a conglomerate of two or more nerve cell bodies, surrounded by common Schwann cells. Direct physical contact between ganglion cell membranes (ephapse) was possible, in places where adjacent cells lacked a separating Schwann cell layer (gaps). One such gap was selected, and observed in 57 of 90 consecutive sections. Membrane specializations, observed in 36 sections, were found to be of principally three different types namely: (1) symmetrical, (2) asymmetrical, and (3) asymmetrical subplasmalemmal. The functional properties of these membrane specializations are still unknown. Asymmetrical densities were seen on one or other of the two cell membranes. A graphic model based on serial thin sections was made to illustrate the gap area. Superficially membrane specializations were seen to form small disk-like areas varying in size, the largest measuring 3 x 2 microm. It is speculated whether these unique formations between human spiral ganglion cells, which have not been observed in other species, may constitute interactive electrotonic or ephaptic transmission pathways. These may be in the low-frequency region and may increase plasticity and signal acuity related to the coding of speech.

Expression of Na/K-ATPase subunits in the human cochlea: a confocal and super-resolution microscopy study with special reference to auditory nerve excitation and cochlear implantation

“…The high-intensity display of Na/K-ATPase in the surface membrane of human spiral ganglion neurons in plasma cell membranes of juxtaposed type I cells is intriguing. Interactive transmission pathways through symmetrical and asymmetrical membrane specializations, measuring up to 3 × 2 μm in size, were described between spiral ganglion cell soma (41,42). These were frequent in the apical region and were postulated to sharpen electric signals possibly related to speech coding.…”

“…Axo-somatic synaptic contacts exist on both types I and II cell bodies. Areas with no separating glia layer between type I cell bodies exist in man with both symmetric and asymmetric soma-somatic membrane (41, 42). These connections may couple individual cells electrically.…”

Impact of Morphometry, Myelinization and Synaptic Current Strength on Spike Conduction in Human and Cat Spiral Ganglion Neurons

“…Within such a cluster a close contact of somatic cell membranes is evident. Tylstedt and Rask-Andersen [67] speculate whether unique formations between such human SGCs may constitute interactive electrotonic or ephaptic transmission pathways. These may increase neural synchrony and signal acuity related to the coding of speech.…”

Macrophages in the Human Cochlea: Saviors or Predators—A Study Using Super-Resolution Immunohistochemistry

“…Archival sections were re-analyzed from specimens collected during surgery and earlier publication ( 39 ). In the apical part, where the ganglion cells accumulate, ultrathin serial sections with a thickness of about 800 Å were made and examined by TEM.…”