The Central Projection of Intracellularly Labeled Auditory Nerve Fibers: Morphometric Relationships Between Structural and Physiological Properties

Abstract

The acoustic receptor cells in the cochlea contact the peripheral processes of primary auditory neurons, called spiral ganglion (SG) cells. The central processes of SG cells bundle together to form the auditory nerve (AN) and project into the cochlear nucleus (CN). Through this pathway, transduced acoustic information is conveyed directly as input to the brain. Essentially all of our knowledge concerning the nature of this input via the AN is derived from the myelinated axon of type-I SG cells. Type I neurons innervate inner hair cells exclusively (Kiang et al., 1982) and represent 90–95% of the SG population (Spoendlin, 1971). Virtually nothing is known about the functional properties of the type-II SG cells which innervate outer hair cells and comprise the remainder of the SG population.