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Physiology of the hearing (II) (Learning objective: 103)

Dr. Attila Nagy

2019

The inner ear

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Longitudinal section of the unfolded cochlea

Cross section of the cochlea

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Cross section of the cochlea

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The organ of Corti

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Endocochlear potential

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Hair cells

• About 16,000 in each cochlea

• BM vibrates due to ∆P between tubes

• Deformation of hair cells

• Opening of ion channels

• Ions flow and stimulate nerve endings attached to hair cell

http://biology-web.nmsu.edu/serrano/neurolab/imagegallery/imagegallery.html

Innervation of the hair cells

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Frequency tuning of the hair cells on the basilar membrane

The structure of the hair cells

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Stimulation Inhibition

Tip links

stretched

Tip links

relaxed

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Histopathology

• Acoustic Trauma

Histopathology

• Acoustic Trauma

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Path of sound in the inner ear

• Wave moves through scala vestibuli

• Passes though helicotrema into scala tympani

• Passes down scala tympani to round window

• Exits cochlea via round window

• Both tubes are filled with perilymph

Face plate of the stapes

Base Apex

Frequency analysis in the cochlea

1. Migrating wave on the basilar

membrane

2. Active contraction of the outer hair cells

3. Transmitter release from the inner hair

cells

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• BM varies in thickness and stiffness

along its length

• Different sections are resonant at

different frequencies

– High at beginning

– Low at end

• Not linear, however

– Each octave requires about 3.5 to 4.0 mm

1. Migrating wave on the basilar membrane

The Nobel Prize in

Physiology or Medicine

1961

"for his discoveries of the

physical mechanism

of stimulation within the

cochlea"

The migrating wave on the basilar membrane

Békésy György (Georg von Békésy)

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How do we

determine pitch?

This section of

the cochlea’s

basilar

membrane

contain hair cells

sensitive to low

frequencies (long

wavelengths).

This section

contain hair

cells sensitive to

high

frequencies

(short

wavelengths)

PLACE

THEORY

Tonotopy

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The basilar membrane

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2. Active contraction of the outer hair cells

-60mV

-30mV

ca 5 %

Source: www.physiol.ucl.ac.uk/ashmore/jfa.htm

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Prestin – voltage dependent change of the lenght of the outer hair cell

-60 mV

-30 mV

Prestin – voltage dependent change of the lenght of the outer hair cell

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-60 mV

Prestin – voltage dependent change of the lenght of the outer hair cell

The outer hair cells amplify the movement of the endolymph and the tuning of the basilar membrane

outer hair cell

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Stimulation Inhibition

Tip links

stretched

Tip links

relaxed

3. Transmitter release from the inner hair cells

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Hair cells will be activated quickly

RodsCons

Schematic summary about the signal transduction in the inner ear

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Central auditory pathways

Tonotopical organization

Central auditory pathways

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Coding of sound intensity

Binaural hearing

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Auditory evoked potentials

Auditory evoked potentials

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1. Soundwaves cause

air pressure changes in

the auditory canel.

2. The eardrum

vibrates and the

vibrations are

transmitted to the

inner ear (hammer,

anvil, stirrup).

3. The stirrup vibrates

the wall of the cochlea,

creating waves in the

fluid inside.

4. Fluid moves

hair cells on

the basilar

membrane

generating a

nerve impulse.

Summary