ABA Transmission & Drivetrain Systems 2 — Questions and Answers
Question 1: What is the primary role of the ossicular chain in auditory transmission?
- Convert electrical signals to mechanical vibrations
- Impedance match the air-filled ear canal to the fluid-filled cochlea (Correct answer)
- Amplify neural signals in the auditory cortex
- Filter high-frequency sounds before cochlear entry
Correct answer: Impedance match the air-filled ear canal to the fluid-filled cochlea
The ossicular chain (malleus, incus, stapes) acts as a mechanical transformer that matches the low impedance of air to the high impedance of cochlear fluids.
Question 2: The lever action of the ossicular chain contributes approximately how much gain in sound pressure?
- 1.3 dB
- 5.6 dB (Correct answer)
- 13 dB
- 25 dB
Correct answer: 5.6 dB
The ossicular lever ratio (malleus arm to incus arm) provides approximately 1.3:1 mechanical advantage, contributing about 2 dB of the total middle ear gain.
Question 3: Which structural feature of the tympanic membrane–stapes footplate area ratio contributes most to middle ear transformer gain?
- Tympanic membrane curvature (catenary action)
- Area ratio of tympanic membrane to stapes footplate (~17:1) (Correct answer)
- Thickness differential between the two membranes
- Eustachian tube pressure equalization
Correct answer: Area ratio of tympanic membrane to stapes footplate (~17:1)
The ~17:1 area ratio between the tympanic membrane and stapes footplate concentrates force onto a smaller area, yielding approximately 25 dB of pressure gain.
Question 4: Disruption of which ossicle most severely compromises the transmission 'drivetrain' if completely separated?
- Malleus handle
- Malleus head
- Incudo-stapedial joint (Correct answer)
- Stapes arch
Correct answer: Incudo-stapedial joint
Separation at the incudo-stapedial joint breaks the ossicular chain entirely, causing a maximal conductive hearing loss of approximately 60 dB HL.
Question 5: Bone conduction bypasses which component of the auditory transmission drivetrain?
- Cochlear hair cells
- The outer and middle ear (Correct answer)
- The auditory nerve
- The basilar membrane
Correct answer: The outer and middle ear
Bone conduction transmits vibration directly through the skull to the cochlea, bypassing the outer ear canal and middle ear mechanics.
Question 6: What phenomenon explains why the acoustic reflex stiffens the ossicular chain during loud sounds?
- Increased endolymph pressure
- Tensor tympani and stapedius muscle contraction (Correct answer)
- Eustachian tube dilation
- Outer hair cell electromotility
Correct answer: Tensor tympani and stapedius muscle contraction
The stapedius (primarily) and tensor tympani muscles contract reflexively, stiffening the ossicular chain and reducing low-frequency transmission to protect the cochlea.
Question 7: Otosclerosis primarily impairs transmission by affecting which part of the ossicular drivetrain?
- Malleus head fixation in the epitympanum
- Bony fixation of the stapes footplate in the oval window (Correct answer)
- Erosion of the incus long process
- Perforation of the tympanic membrane
Correct answer: Bony fixation of the stapes footplate in the oval window
Otosclerosis is characterized by abnormal bone remodeling that fixes the stapes footplate, preventing its piston-like motion and causing conductive hearing loss.
ABA Transmission & Drivetrain Systems 2
What is the primary role of the ossicular chain in auditory transmission?