HIS Ear Anatomy & Physiology 3 — Questions and Answers
Question 1: 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 2: 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 3: 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 4: 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 5: 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 6: 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 7: 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.
HIS Ear Anatomy & Physiology 3
What is the tonotopic organization of the cochlea, and where are high-frequency sounds processed?