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Physiology of hearing and hearing loss

Question
10 out of 39
 

Bones of middle ear are responsible for which of the following? (LQ)



A Amplification of sound intensity

B Reduction of sound intensity

C Protecting the inner ear

D Reduction of impedance to sound transmission

Ans. D Reduction of impedance to sound transmission

We have discussed in detail the mechanism of hearing in the previous question. Broadly hearing mechanism can be divided into:

Mechanical conduction of sound (done by middle ear).

Transduction of mechanical energy into electrical impulses (done by sensory system of cochlea)

Conduction of electrical impulse to brain (. auditory pathway)

Detailed Information

i. Conduction of sound:

It is done mainly by middle ear. Middle ear not just simply conducts the sound but converts sound of great amplitude & less force to that of less amplitude and greater force. This function of the middle ear is called as impedance matching mechanism or the transformer action.

This function of middle ear is accomplished by

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ii. Transduction of mechanical energy to electrical impulse:

Movements ofthe stapes footplate causes vibrations in scala vestibuli followed by scala tympani and is transmitted to the cochlear fluids which brings about movement of the basilar membrane. This sets up shearing force between the tectorial membrane and the hair cells. The distortion of hair cells gives rise to electrical nerve impulse.

Note

A sound wave, depending on its frequency, reaches maximum amplitude on a particular place on the basilar membrane, and stimulates that segment (traveling wave theory of van Bekesy). Higher frequencies are represented in the basal turn of cochlea and the progressively lower one toward the apex.

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Frequency localization in the cochleA. Higher frequencies are

localized in the based turn and the progressively decrease toward the apex.

iii. Neural pathway/Auditory pathway:

Hair cells get innervation from bipolar cells of spiral ganglion. Central axons of these cells collect to form the cochlear nerve.

(Cochlear division of VIII nerve) and end in the cochlear nuclei (the dorsal and ventral on each side of medulla).

From cochlear nuclei crossed & uncrossed fibers pass via superior olivary nucleus complex nucleus of lateral lemniscus inflerior colliculus Medial geniculate body & finally reach the auditory cortex of the temporal lobe.

Physiology of hearing and hearing loss Flashcard List

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