Neuroanatomical basis of cochlear coding mechanisms.

The afferent cochlear neurons to outer and inner hair cells differ not only in their relative numbers (95% to inner hair cells and only 5% to outer hair cells) and distribution pattern (great convergence for outer hair cells and divergence for inner hair cells) but also in their degeneration behaviour and metabolism. Some special afferent fibres seem to exist. The afferent neurons present three types of ganglion cells in the spiral ganglion with no morphological evidence for an extensive direct interaction between afferent neurons of the outer and the inner hair cell system at any level in the cochlea and even their efferent nerve supply is essentially separated.