HIS Ear Anatomy & Physiology — Questions and Answers

Question 1: Which structure connects the middle ear to the nasopharynx and helps equalize pressure?

Eustachian tube (Correct answer)
External auditory meatus
Semicircular canal
Round window

Correct answer: Eustachian tube

The Eustachian tube (auditory tube) connects the middle ear cavity to the nasopharynx, allowing pressure equalization on both sides of the tympanic membrane.

Question 2: The oval window is a membrane-covered opening that connects which two structures?

Middle ear to inner ear (Correct answer)
Outer ear to middle ear
Cochlea to vestibule
Semicircular canals to cochlea

Correct answer: Middle ear to inner ear

The oval window is a membrane-covered opening in the bony wall separating the middle ear from the inner ear, where the stapes footplate transmits vibrations.

Question 3: Which type of hair cells in the cochlea are primarily responsible for active amplification of sound?

Outer hair cells (Correct answer)
Inner hair cells
Pillar cells
Deiters' cells

Correct answer: Outer hair cells

Outer hair cells (OHCs) are electromotile and provide active mechanical amplification of basilar membrane motion, boosting sensitivity by up to 40–60 dB.

Question 4: What is the primary function of the round window in the cochlea?

To allow fluid pressure to dissipate after oval window displacement (Correct answer)
To support the tectorial membrane
To separate the scala media from the scala tympani
To house the spiral ganglion neurons

Correct answer: To allow fluid pressure to dissipate after oval window displacement

The round window membrane flexes outward when the oval window is pushed inward, allowing incompressible cochlear fluid to move and basilar membrane displacement to occur.

Question 5: Reissner's membrane separates which two compartments of the cochlea?

Scala vestibuli from scala media (Correct answer)
Scala media from scala tympani
Scala tympani from scala vestibuli
Helicotrema from scala vestibuli

Correct answer: Scala vestibuli from scala media

Reissner's membrane forms the upper wall of the scala media (cochlear duct), separating it from the perilymph-filled scala vestibuli above.

Question 6: The endolymph found in the scala media is unusual because it has a high concentration of which ion?

Potassium (K+) (Correct answer)
Sodium (Na+)
Calcium (Ca2+)
Chloride (Cl-)

Correct answer: Potassium (K+)

Unlike most extracellular fluids, endolymph has a very high potassium ion concentration (~150 mM), which is essential for generating the endocochlear potential.

Question 7: Which cranial nerve transmits auditory information from the cochlea to the brainstem?

CN VIII (vestibulocochlear nerve) (Correct answer)
CN VII (facial nerve)
CN V (trigeminal nerve)
CN IX (glossopharyngeal nerve)

Correct answer: CN VIII (vestibulocochlear nerve)

The cochlear branch of cranial nerve VIII (vestibulocochlear nerve) carries afferent signals from the spiral ganglion neurons to the cochlear nuclei in the brainstem.

Question 8: What is the tonotopic organization of the cochlea, and where are high-frequency sounds processed?

High frequencies near the base, low frequencies near the apex (Correct answer)
High frequencies near the apex, low frequencies near the base
High frequencies in the middle turns, low at both ends
Frequency mapping is uniform throughout the cochlea

Correct answer: High frequencies near the base, low frequencies near the apex

The cochlea is tonotopically organized: high-frequency sounds cause maximum basilar membrane displacement near the stiff basal end, while low frequencies peak near the flexible apex.

Question 9: The tensor tympani muscle attaches to which ossicle and is innervated by which nerve?

Malleus; CN V (trigeminal) (Correct answer)
Stapes; CN VII (facial)
Incus; CN IX (glossopharyngeal)
Malleus; CN VII (facial)

Correct answer: Malleus; CN V (trigeminal)

The tensor tympani inserts on the handle of the malleus and is innervated by the medial pterygoid branch of the mandibular division of the trigeminal nerve (CN V3).

Question 10: The acoustic (stapedial) reflex protects the cochlea from loud sounds by causing the stapedius muscle to do what?

Stiffen the ossicular chain, reducing low-frequency energy transmission (Correct answer)
Relax the ossicular chain, increasing sound transmission
Dilate the Eustachian tube to equalize pressure
Contract the tensor tympani to seal the oval window

Correct answer: Stiffen the ossicular chain, reducing low-frequency energy transmission

Stapedius contraction tilts the stapes and stiffens the ossicular chain, attenuating primarily low-frequency sounds reaching the cochlea by 10–15 dB.

Question 11: Hair cell stereocilia are arranged in rows of increasing height. What happens when they are deflected toward the tallest row?

Tip links open mechanosensitive ion channels, depolarizing the hair cell (Correct answer)
Tip links close mechanosensitive ion channels, hyperpolarizing the hair cell
Stereocilia detach from the tectorial membrane
Potassium exits the cell through basolateral channels

Correct answer: Tip links open mechanosensitive ion channels, depolarizing the hair cell

Deflection toward the tallest stereocilia stretches tip links, pulling open mechanosensitive (MET) channels so K+ and Ca2+ flow in, depolarizing the hair cell.

Question 12: The pinna's primary role in sound localization involves which acoustic cue?

Spectral shaping of sound that helps determine elevation and front-back discrimination (Correct answer)
Interaural time differences for azimuth localization
Amplification of interaural level differences
Filtering out low-frequency ambient noise

Correct answer: Spectral shaping of sound that helps determine elevation and front-back discrimination

The ridges of the pinna create direction-dependent spectral filtering (head-related transfer function) that the auditory system uses for vertical and front-back localization.

Question 13: Which structure within the cochlea produces endolymph and maintains the endocochlear potential?

Stria vascularis (Correct answer)
Spiral ligament
Organ of Corti
Spiral ganglion

Correct answer: Stria vascularis

The stria vascularis, located on the lateral wall of the scala media, actively secretes endolymph and generates the +80 mV endocochlear potential that drives hair cell transduction.

Question 14: What is the approximate frequency range of normal human hearing?

20 Hz to 20,000 Hz (Correct answer)
200 Hz to 20,000 Hz
20 Hz to 2,000 Hz
2 Hz to 200,000 Hz

Correct answer: 20 Hz to 20,000 Hz

The normal human auditory frequency range is approximately 20 Hz to 20,000 Hz (20 kHz), with greatest sensitivity between 1,000 and 4,000 Hz.

Question 15: Damage to outer hair cells most commonly results in which type of hearing loss pattern on an audiogram?

Sensorineural hearing loss, typically worse at high frequencies (Correct answer)
Conductive hearing loss with air-bone gap
Flat sensorineural loss across all frequencies
Low-frequency cookie-bite pattern

Correct answer: Sensorineural hearing loss, typically worse at high frequencies

OHCs at the basal (high-frequency) end of the cochlea are most vulnerable to noise and ototoxins, producing the classic high-frequency sloping sensorineural loss.

Question 16: The helicotrema is located at which end of the cochlea and serves what function?

Apex; connects scala vestibuli and scala tympani so fluid can flow between them (Correct answer)
Base; separates cochlear from vestibular fluid spaces
Middle turn; equalizes pressure between scala media and scala tympani
Apex; houses the spiral ganglion cell bodies

Correct answer: Apex; connects scala vestibuli and scala tympani so fluid can flow between them

The helicotrema is a small opening at the cochlear apex where the scala vestibuli and scala tympani communicate, allowing very-low-frequency fluid pressure to equalize.

Question 17: Which of the three ossicles is directly attached to the tympanic membrane?

Malleus (Correct answer)
Incus
Stapes
All three ossicles contact the tympanic membrane

Correct answer: Malleus

The handle (manubrium) of the malleus is embedded in the fibrous layer of the tympanic membrane, making it the first ossicle to receive vibrations from the eardrum.

Question 18: The impedance mismatch between air and cochlear fluid is overcome by the middle ear transformer. What is the primary mechanism?

Hydraulic lever effect from the large tympanic membrane area relative to the small oval window area (Correct answer)
Bony resonance amplification in the ossicular chain
Air pressure built up in the middle ear cavity
Tensor tympani pre-tensioning the ossicles

Correct answer: Hydraulic lever effect from the large tympanic membrane area relative to the small oval window area

The tympanic membrane's area (~55 mm²) is about 17–20 times larger than the oval window (~3.2 mm²), concentrating force and providing most of the ~25–30 dB pressure gain needed to overcome the air-to-fluid impedance barrier.

Question 19: Otoacoustic emissions (OAEs) are generated by which cochlear structure?

Outer hair cells (Correct answer)
Inner hair cells
Spiral ganglion neurons
Tectorial membrane

Correct answer: Outer hair cells

OAEs are sounds produced by the active electromotility of outer hair cells; they travel backward through the middle ear and can be recorded in the ear canal with a sensitive microphone.

Question 20: The vestibular system detects head rotation using which sensory end organ?

Semicircular canals with crista ampullaris (Correct answer)
Utricle and saccule with maculae
Cochlear apex with helicotrema
Round window membrane

Correct answer: Semicircular canals with crista ampullaris

The three semicircular canals detect angular (rotational) acceleration; their ampullae contain the crista with hair cells embedded in the cupula, which deflects with endolymph movement.

Question 21: The tympanic membrane is divided into two main regions. The smaller, less mobile superior portion is called the:

Pars flaccida (Correct answer)
Pars tensa
Annulus fibrosus
Umbo

Correct answer: Pars flaccida

The pars flaccida (Shrapnell's membrane) is the superior portion of the tympanic membrane lacking the fibrous middle layer, making it more flaccid and susceptible to retraction pockets and cholesteatoma formation.

HIS Ear Anatomy & Physiology

Which structure connects the middle ear to the nasopharynx and helps equalize pressure?

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