صدق الله العظيم الاسراء اية 58

By Dr. Abdel Aziz M. Hussein Lecturer of Physiology Member of American Society of Physiology

It connects the middle ear with the nasopharynxFunctions: 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

Cochlea Vestibular apparatus

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

2) Transmission of sound waves in the cochlea (the traveling wave):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

3) Receptor potential and generation of cochlear nerve impulse: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 Ca 2+ channels, opening them causing Ca 2+ 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 Ca 2+ channels and release of chemical transmitter.

THANKS