Formation of the cochlear nerve in the modiolus of the guinea pig and human cochleae

Abstract

Background: Central processes of the bipolar neurons in the spiral ganglion converge in the modiolus to form the initial portion of the auditory branch (cochlear nerve) of the eighth cranial nerve. This occurs before the cochlear nerve passes through the internal auditory meatus. The neurons of the spiral ganglion send their central processes towards the internal acoustic meatus, through a single canal to form the cochlear nerve. These processes are described in many textbooks as running through numerous longitudinal small canals called canales longitudinales modioli before entering the internal acoustic meatus. Results of this study indicated that the term; "canalis longitudinalis modioli" was considered to be more appropriate than the former.

Methods: Central processes of the bipolar neurons in the spiral ganglion of the guinea pig and human cochleae were investigated using stereo, light and electron microscopy.

Results: Detailed examination of the guinea pig and human cochleae by light, electron and stereomicroscopy did not reveal multiple longitudinal canals but a single canal for the cochlear nerve.

Conclusions: The singular term canalis longitudinalis modioli is more appropriate than canales longitudinales modioli.