HIS Anatomy of the Auditory System

Question 1

What are the three ossicles of the middle ear and what is their function?

Accepted Answer

Malleus, incus, stapes—they form a mechanical lever system that transmits and amplifies vibrations from the tympanic membrane to the oval window of the cochlea

Answer

Cochlea, vestibule, semicircular canals—they convert electrical signals to sound

Answer

Eustachian tube, round window, oval window—they equalize pressure in the middle ear

Answer

Helicotrema, basilar membrane, Reissner's membrane—they separate cochlear compartments

Question 2

What is the function of the Eustachian tube?

Accepted Answer

To equalize air pressure between the middle ear cavity and the nasopharynx (atmosphere), maintaining the pressure differential needed for optimal tympanic membrane vibration

Answer

To transmit sound from the outer ear to the middle ear

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To drain endolymph from the cochlea

Answer

To connect the cochlea to the vestibular system

Question 3

What is the basilar membrane and how does it contribute to frequency analysis in the cochlea?

Accepted Answer

A membrane running the length of the cochlea that is narrow and stiff at the base (responding to high frequencies) and wider and more flexible at the apex (responding to low frequencies), creating a tonotopic frequency map

Answer

The outer membrane of the tympanic cavity that vibrates to sound

Answer

The membrane separating scala vestibuli from scala media

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A stiff membrane that reflects high-frequency sounds away from the cochlea

Question 4

What is the role of the outer hair cells (OHCs) in the cochlea?

Accepted Answer

To act as active mechanical amplifiers, changing length in response to electrical signals (electromotility) to boost basilar membrane vibration and sharpen frequency tuning—they power the cochlear amplifier

Answer

To transduce sound and send action potentials to the auditory nerve (same as inner hair cells)

Answer

To produce endolymph and maintain the endocochlear potential

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To stabilize the basilar membrane against excessive displacement

Question 5

Which cranial nerve carries auditory and vestibular information from the inner ear to the brainstem?

Accepted Answer

Cranial nerve VIII (vestibulocochlear)

Answer

Cranial nerve V (trigeminal)

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Cranial nerve VII (facial)

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Cranial nerve IX (glossopharyngeal)

Question 6

What is the endocochlear potential and why is it important for hearing?

Accepted Answer

A +80 mV electrical potential in the endolymph of the scala media produced by the stria vascularis, which drives ion flow through hair cell transduction channels and powers sound transduction

Answer

The voltage generated by the tympanic membrane during vibration

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The resting potential of spiral ganglion neurons

Answer

The voltage required to activate the stapedius muscle reflex