Auditory Nerve Anatomy

Two branches of CN VIII

Auditory ~30,000 fibers

Vestibular ~20,000 fibers

The slightly enlarged area that houses the spiral ganglion

Rosenthal’s canal

Nerve cells do what

Process information

Glial cells function

metabolic support

do not fire action potentials 

Remove dead cell bodies and clean up the nervous system

Parts of the neuron

Cell body

dendrites

axon

Myelin sheath

insulates axon, produced by Schwann cells

Myelinated vs unmyelinated neuron

myelinated nerve fibers increase signal speed

Basic types of neruons

unipolar

bipolar

pseudounipolar

multipolar

What is the only neuron that’s found with olfactory, vision, and hearing systems?

bipolar

Afferent neurons

sensory neurons

bring sensory information up

Efferent neurons

motor neurons

sends information to muscles and glands

Interneurons

Connect to other neurons

Afferent nerve fiber innervation

Type I fibers

Type II fibers

Type I fibers

90-95%

inner radial fibers

IHC

many to one: 8 fibers to 1 IHC

Type II fibers

5-10%

outer spiral fibers

OHC

one to many: 1 fiber to 10 OHCs

Efferent nerve fiber innervation

from SOC

lateral olivocochlear (LOC)

medial olivocochlear (MOC)

LOC

IHC

unmyelinated

modulates neurons

MOC

OHC

myelinated

provides negative-feedback loop

Auditory nerve bundle: middle

Apical innervation

low freq

Auditory nerve bundle: outer

basal innervation

high freq

CPA

houses CN VIII

Where do most vestibular schwannoma masses originate

vestibular brance of CN VIII

Vestibular schwannoma clinical signs and sx

Vertigo

pulsatile tinnitus

SNHL (starts with high freq because pressing on the outside bundles)