Transcript Hearing part II

‫بسم هللا الرحمن الرحيم‬
‫﴿و ما أوتيتم من العلم إال قليال﴾‬
‫صدق هللا العظيم‬
‫االسراء اية ‪58‬‬
By
Dr. Abdel Aziz M. Hussein
Lecturer of Physiology
Member of American Society of Physiology
•It connects the middle ear with
the nasopharynx
Functions:
1) It equalizes the pressure on
both sides of the tympanic
membrane.
•This is important for its proper
function as resonator.
•Normally the tube is closed
2) Continual renewal of air in the
middle ear. The air in the middle
ear is normally self-changed and
held there by a valve in the
Eustachian tube.
Otitic Barotrauma
• During ascent of an airplane, the external pressure is
decreased and the Eustachian tube is closed to
equalize the pressure on both sides of the drum.
• During rapid descent of an airplane, the external
pressure increases and pushes the drum inwards
and may rupture it unless the person swallows
•
Reflex contraction of both tensor tympani and
stapedius ms in response to sounds of high intensity
and low frequency (above 80 dB and below 1000 Hz)
Mechanism
•
It has a long latent period (about 40 m.sec)
Importance
1. It protects the cochlea from the damaging vibrations caused
by very loud sound which is usually of low frequency
2. It masks low frequency sounds in loud
environments
3. It decreases the person's hearing sensitivity
to his own speech
If sound waves strike the two windows simultaneously
The effect could be the same as that produced by making
equal pressure on the two ends of an open U tube filled with
water i.e. there would be no displacement of fluid, this is
called cancellation effect
There is condensation phase, at the oval window there will
be rarefaction phase at the round window
The round window serves as a relief hole in the bony cochlea
Vestibular
apparatus
Cochlea
1) Transmission of sound waves in the outer and
middle ear:
• The ear pinna collects and directs the sound waves toward the
external auditory canal.
• Sound waves cause vibrations of the tympanic membrane at
the same frequency.
• Movements of the tympanic membrane are transmitted and
amplified by the bony ossicles of the middle ear to the oval
window via the footplate of the stapes.
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
• 2) Transmission of sound waves in the cochlea (the
traveling wave):
• Rapid movements of the tympanic membrane in response to
sound waves result in traveling waves that move in the basilar
membrane from base to apex.
• Because the basilar fibers are not similar, they increase in
length from base to apex (12 folds) and decrease in stiffness
from base to apex (100 folds)
• A high frequency sound generates a wave that travels for a
short distance and reaches maximum near the base of the
cochlea, while a low frequency sound generates a wave that
travels the whole distance along the basilar membrane to reach
its maximum near the apex
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
• 3) Receptor potential and generation of cochlear nerve
impulse:
• Up and down movements of the basilar membrane create a
shearing force in the tectorial membrane that leads to
depolarization or hyperpolarization of the receptor cells.
• Bending of the stereocilia toward the kinocilium opens the
apical channels leading to influx of K+ with cellular
depolarization and activation of Ca2+ channels, opening them
causing Ca2+ influx, that triggers the release of an excitatory
transmitter, probably glutamate.
• Bending of the stereocilia away from the kinocilium closes the
apical channels leading to cellular hyperpolarization and
inhibition of Ca2+ channels and release of chemical transmitter.
THANKS