Anatomy of the Auditory System Flashcards

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

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

The malleus attaches to the tympanic membrane, connects to the incus, which connects to the stapes whose footplate covers the oval window—they transmit and amplify sound vibrations across the middle ear by approximately 25-30 dB through mechanical advantage.

What is the function of the Eustachian tube?

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

The Eustachian tube connects the middle ear to the nasopharynx and opens briefly during swallowing and yawning to equalize middle ear pressure with atmospheric pressure, essential for normal tympanic membrane function.

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

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

The basilar membrane has graded mechanical properties creating a traveling wave that peaks at different locations for different frequencies—high frequencies peak near the base, low frequencies near the apex—forming the cochlea's tonotopic frequency map.

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

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

Outer hair cells are unique mechanomotor cells that amplify basilar membrane motion through voltage-driven length changes (electromotility via prestin), enhancing sensitivity by 40-60 dB and sharpening frequency selectivity—damage to OHCs is the most common cause of sensorineural hearing loss.

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

Answer: Cranial nerve VIII (vestibulocochlear)

The vestibulocochlear nerve (CN VIII) has two divisions: the cochlear branch (auditory information from the spiral ganglion and hair cells) and the vestibular branch (balance information from the semicircular canals and otolith organs).

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

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

The endocochlear potential (EP) is a +80 mV resting potential maintained by the stria vascularis in scala media; combined with the hair cell resting potential of approximately -45 mV (IHC) or -70 mV (OHC), it creates a driving force for mechanotransduction when stereocilia deflect.