Auditory Nerve Anatomy and Physiology

How many branches of nerves are there of the vestibulocochlear nerve?

2

How many nerve fibers are there on the vestibular nerve?

~20,000

Define scarpa’s ganglia

houses cell bodies of vestibular primary afferent neurons

What does the superior vestibular nerve innervate?

anterior and lateral SCC, utricle, and part of the saccule

What does the inferior vestibular nerve innervate?

posterior SCC and part of the saccule

Define Rosenthal’s canal

in the spiral lamina where the spiral ganglion nerves converge

Define Habenula Perforata

bony opening for fibers to pass through

True or False: each scala media has a Rosenthal’s canal to bunfle the fibers

true

Define spiral ganglion

is a collection of nerve cell bodies

Name the two types of cells in the nervous system

nerve cells (neurons) and glial cells

True or false: glial cells are surrounded by neurons

false; neurons are surrounded by glial cells

Where do peripheral nervous system cells attach to?

attaches to neurons and are myelinated to make transduction faster for neurons

All neurons have what?

cell body (soma), dendrites, and axons

What is the purpose of dendrites?

receive input from other neurons

Define myelin sheath

fatty substance that surrounds the axon

What produces myelin?

Schwann cells

What are nodes of Ranvier?

spaces between the myelin sheath that helps facilitates the rapid transduction of nerves

Where are the myelinated neurons located

near Rosenthal’s Canal

True or false: multipolar neurons are the most common type of neuron

true

Name the basic types of neurons

unipolar, bipolar, pseudounipolar, and multipolar

What are the two types of neurons?

sensory and motor

Multipolar nerve sending information

from brain to body

Define sensory neurons

sensitive to sensory stimuli and connect to sensory receptors

Afferent nerve fibers process information

from PNS to CNS

Define motor neurons

end directly on muscles and glands

Efferent nerve fibers have information going

from CNS to PNS…ends at muscles and glands

Define interneurons

neuron type that connects to other neurons

In Type 1 afferent neurons, it is responsible for which type of hair cell?

inner hair cells; has 8 fibers to 1 inner hair cell

In Type 2 afferent neurons, it is responsible for which type of hair cell?

outer hair cell; has 1 fiber to 10 OHC

Efferent nerve fiber innervation starts…

from the superior olivary complex

Lateral olivocochlear is important for

balance input and output

Medial olivocochlear is important for…

speech in noise hearing and ear protection

Name the aspects of lateral olivocochlear

IHC, unmyelinated, and modulates sensory neurons

Name the aspects of medial olivocochlear

OHC, myelinated, and provides negative-feedback loop

Central part of the auditory nerve bundle is located where and is responsible for what sounds?

apical end of cochlea and low frequency sounds

Peripheral part of the auditory nerve bundle is located where and is responsible for what sounds?

basal end of cochlea and high frequency sounds

What is the tonotopic arrangement of the auditory nerve fiber

high-low-high

Define the cerebellopontine angle

where the auditory nerve enters the brainstem; between the pons and cerebellum

Nerve fiber goes from

lateral to medial; will twist clockwise

Vestibular schwannomas account for what percentage of CPA tumors

80%

Define graded potential

amplitude increases in proportional to the amount of stimulation

Define action potential

a spike occurs when input from hair cell reaches threshold

Fill in the blank: cochlear microphonic reflects ___________ changes from hair cell activity

alternating current

Fill in the blank: summating potential reflects ___________ changes as the hair cell responds to sound

sustained direct-current

True or false: an increase of stimulus also increases the firing rate

true

Define firing rate

number of action potentials per second

True or false: nerve fibers don’t have a spontaneous firing rate when there is no stimulus

false

Nerve fibers encode pitch based on

intensity and frequency

Define characteristic frequency

the frequency that a nerve fiber responds to best

True or false: characteristic frequency is determined by where the fiber connects on the basilar membrane

true

Tuning curves show what?

how sensitive a fiber is across frequencies

Low characteristic frequency fibers are…

broader, symmetric and rounder

High characteristic frequency fibers are…

narrower, asymmetric, and sharper

Define volley principle

at higher frequencies where multiple fibers share the load

Define phase-locking

at low frequencies where spikes occur at the same phase of the sound wave

True or false: firing patterns are made when stimulus it at and above threshold

false; above threshold only

True or false: dynamic range starts at threshold and ends at saturation

true

Auditory nerve fibers have a dynamic range of

40 dB

Define characteristics of low spontaneous rate fibers

towards the modiolus, high threshold, activated by moderate-low sound, wide dynamic range

Define characteristics of high spontaneous rate fibers

towards tunnel of Corti, low threshold, responds to soft sounds, narrow dynamic range