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The Peripheral Auditory System. George Pollak Section of Neurobiology. 1. Hair cells, the transducers of the auditory system, and how they work. stereocillia of inner hair cells. stereocillia of outer hair cells. Organ of Corti. Basilar membrane. stereocilia on one hair cell. 9.

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The Peripheral Auditory System

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The Peripheral Auditory System

George Pollak

Section of Neurobiology


1

  • Hair cells, the transducers of the auditory system, and how they work.

stereocillia of

inner hair cells

stereocillia of

outer hair cells

Organ of Corti

Basilar membrane


stereocilia on one hair cell


9


Potential difference between

Endolymphand cell interior

Potential difference between

Perilymph and cell interior

Kout

Kout

endolymph

= 0mV

= ~-70mV

Ek= 58 log

Ek= 58 log

Kin

Kin

Hi K+

Lo Na+

Hi K+

Lo Na+

Hi Na+

Lo K+

perilymph


-45 mV


Hi K+

low Na+

Hi K+

low Na+

Hi K+

low Na+

Hi Na+

low K+

Hi Na+

low K+


small leakage of

K+ into cell

No K+ into cell

K+ into cell

-45 mV

-70 mV


Next, we are going to

build a cochlea


Stapes

Basilar membrane


Sound is changed from

a pressure wave in the air

into mechanical movements

on the basilar membrane


round window


Traveling waves on basilar membrane

oval window

round window


The structure of the

basilar membrane causes it

to perform a

frequency to place transformation


Apex

responds maximally to low frequencies

flexible

wide and thin

Stiff

Narrow and thick

Base

responds maximally to high frequencies

Basilar Membrane

has continuously changing dimensions along its length


Basilar membrane converts frequency to a place of maximal response


Frequency-to-Place Transformation in the Cochlea


The motion on the

basilar membrane

causes shearing of the cilia on

hair cells and thereby causes

the hair cells to

depolarize and hyperpolarize in

response to sound


Organ of Corti

Basilar membrane


shearing of stereocillia

Organ of Corti

basilar membrane

basilar membrane


Why are there two types of

hair cells?


98% of the fibers that project into the central auditory system

are innervated by inner hair cells!!

98%


What are the outer hairs doing?

Answer: they act as amplifiers

of the mechanical motion of

the basilar membrane generated

by sound


release of transmitter

Hi K+

K+

-----

depolarization

hyperpolarization


Evoked mechanical responses of isolated cochlear outer hair cells.

_

+

_

+

_

+

Electromotility: OHC can change length in response to voltage change

Direct evidence of an active mechanical process in the organ of Corti

depolarized

hyperpolarized


Dancing hair cell

42


Outer hair cells are the only cells in the body that express prestin. Even inner hair cells do NOT have prestin.

+

+

+

+

+

+

+

+


Show movie of how Prestin works


Positive feedback loop

Basilar membrane motion

Sound stimuli

Hair bundle deflection

Change in length of hair cells

Membrane potential change

OHC

IHC

Sensory signal transmission


Normal response with cochlear amplifier

Apex

base

Basilar membrane

response without cochlear amplifier

Apex

base


How motion of basilar membrane

generates tuning curves in

auditory nerve fibers and thereby

imparts frequency selectivity

to auditory nerve fibers


5

50 dB SPL

6

7

8

10

11

9

Frequency ( kHz)

base

apex

6 kHz

60

7 kHz

50

40

Intensity (dB SPL)

8 kHz

30

20

9 kHz

10

10 kHz


30 dB SPL

5

best frequency

6

7

8

10

11

9

Frequency ( kHz)

Tuning Curve

The most basic feature

of an auditory neuron

base

apex

6 kHz

60

7 kHz

50

40

Intensity (dB SPL)

8 kHz

30

20

9 kHz

10

10 kHz


tuning curves in animals with no outer hair cells or

in animals without prestin gene

tuning curves in normal animals

high

Sound intensity

low

low

high

frequency


How is the tonotopic organization

that was first established on the

basilar membrane

preserved in in the

central auditory system?


Auditory cortex

Medial geniculate

Medial geniculate

Inferior

colliculus

Inferior

colliculus

Cochlear nucleus

Cochlear nucleus

Superior olive

Superior olive

Auditory nerve

Auditory nerve

Cochlea

Cochlea

Flow of Information Along the Central Auditory Pathway


superior olive

auditory cortex

medial geniculate

medial geniculate

Inferior colliculus

Inferior colliculus

cochlear nucleus

cochlear nucleus

Auditory cortex

Medial geniculate

Medial geniculate

Inferior

colliculus

Inferior

colliculus

Cochlear nucleus

Cochlear nucleus

Superior olive

Superior olive

Auditory nerve

Auditory nerve

Cochlea

Cochlea

The Frequency Representation on the Cochlea is Preserved in Every Nucleus of the Central Auditory System, and thus the Auditory System is Tonotopically Organized


Auditory cortex

Medial geniculate

Medial geniculate

Inferior

colliculus

Inferior

colliculus

Cochlear nucleus

Cochlear nucleus

Superior olive

Superior olive

Auditory nerve

Auditory nerve

Cochlea

Cochlea

The Frequency Representation on the Cochlea is Preserved in Every Nucleus of the Central Auditory System, and thus the Auditory System is Tonotopically Organized


The Frequency Representation on the Cochlea is Preserved in Every Nucleus of the Central Auditory System, and thus the Auditory System is Tonotopically Organized


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