The human round window – a perilymph pressure regulator?On a novel mechanoreceptor‐like neuron in the human round window membrane

Abstract

A medial innervation of the human round window membrane (RWM) was recently discovered in well fixed human tissue using immunohistochemistry. In the present study we used re‐embedding and serial thin section ultrastructural techniques (TEM) to locate and follow these nerve fibres from the spiral ganglion (SG) to the RWM. One neuron projecting through a small perforating bone channel into the RWM could be analysed in detail near the lamina spiralis ossea. Within the middle layer of the RWM it formed a terminal ‘loop’ and was anchored in the stromal tissue. The inward projecting fibre was surrounded by a loose perineural sheath interrupted by gaps where basal lamina faced the extra‐cellular matrix, similar to joint mechanoreceptors. Followed proximally, the neuron branched and formed a unit of several myelinated and un‐myelinated nerve fibres. The cell body was traced to the SG and showed unique ultrastructural features seemingly representing a novel type of ganglion cell unlike the small and large cells normally observed. It is speculated that this nerve supply of the RWM represents a sensory innervation involved in registration of tensile forces during its displacement. Such information could be relayed to nearby located blood vessels thereby playing a role for the regulation of perilymph pressure.

• round window
• electron microscopy
• neuroreceptor
• human
• immunocytochemistry
• synaptophysin