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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