Anatomy of the Auditory Nerve Flashcards
Where do the fibers of the AN originate?
At the base of the cochlear hair cells where the AN contact the bottoms of the hair cells.
What is the course of the AN fibers?
From base, through habenula perforate, then coursing together to form the spiral ganglion cells found in Rosenthal’s canals, before forming trunk of modiolus and coursing out of the cochlea and into/through the IAM.
What does the auditory nerve consist of?
Both afferent and efferent fibers, with more of the fibers being afferent.
What is the habenula perforate?
The bony structure of the osseous spiral lamina that has small openings through which auditory nerve fibers pass.
How many afferent fibers are connected to IHCs? To OHCs?
95% connect to IHCs, and only 5% to OHCs.
How many eighth nerve fibers does each IHC connect to? What is this called?
As many as ten- resulting in a “many to one” ratio.
What does each OHC share its innervation with? What is this called?
Ten other OHCs- resulting in a “one to many” innervation.
What are the two types of fibers found in the VIIIth nerve?
Type I and Type II
What is a Type I fiber? How much do they make up of the VIIIth nerve? What do they innervate?
Large myelinated fibers that make up 95% of the VIIIth nerve. Most innervate IHCs.
What are Type II fibers? What do they innervate?
Small unmyelinated AND myelinated fibers that innervate the OHCs.
Explain efferent innervation of the OHCs…
Inhibitory- reduces afferent output caused by hair cell stimulation.
