CAOHC Physics of Sound and Anatomy 2 — Questions and Answers
Question 1: What is the function of the ossicular chain in the middle ear?
- To amplify and transmit sound vibrations from the tympanic membrane to the oval window (Correct answer)
- To produce the endolymph fluid in the inner ear
- To equalize air pressure between middle ear and environment
- To convert sound waves into electrical nerve impulses
Correct answer: To amplify and transmit sound vibrations from the tympanic membrane to the oval window
The three ossicles form a mechanical lever system that amplifies sound vibrations approximately 25-30 dB as they transfer energy from the tympanic membrane to the oval window.
The ossicular chain provides amplification through the area ratio between the larger tympanic membrane and smaller oval window (approximately 17:1) plus lever action of the bones. This overcomes energy loss at the air-fluid interface.
Question 2: Which structure in the cochlea contains the sensory hair cells responsible for hearing?
- The organ of Corti (Correct answer)
- The Eustachian tube
- The semicircular canals
- The tympanic membrane
Correct answer: The organ of Corti
The organ of Corti contains the inner and outer hair cells that convert mechanical vibrations into electrical nerve impulses.
The organ of Corti contains approximately 3,500 inner hair cells (primary receptors) and 12,000 outer hair cells (cochlear amplifiers). Noise-induced hearing loss primarily results from damage to the stereocilia on these hair cells.
Question 3: What is the frequency range of normal human hearing?
- Approximately 20 Hz to 20,000 Hz (Correct answer)
- 100 Hz to 8,000 Hz
- 500 Hz to 4,000 Hz
- 50 Hz to 50,000 Hz
Correct answer: Approximately 20 Hz to 20,000 Hz
Normal young human hearing spans approximately 20 Hz to 20,000 Hz, with maximum sensitivity between 1,000 and 4,000 Hz.
The ear is most sensitive between 1,000-4,000 Hz due to ear canal resonance and middle ear transfer function. Speech primarily occupies 250-6,000 Hz.
Question 4: What property of sound determines its perceived loudness?
- Amplitude (intensity) (Correct answer)
- Frequency
- Wavelength
- Phase
Correct answer: Amplitude (intensity)
The amplitude or intensity of a sound wave determines how loud it is perceived, measured in decibels.
Every 10 dB increase represents a tenfold increase in sound intensity and is perceived as approximately a doubling of loudness.
Question 5: How does the basilar membrane in the cochlea separate different sound frequencies?
- Through tonotopic organization with the base responding to high frequencies and the apex to low frequencies (Correct answer)
- By vibrating at the same frequency throughout its entire length
- Through chemical neurotransmitter selection at the hair cells
- By rotating within the cochlear duct
Correct answer: Through tonotopic organization with the base responding to high frequencies and the apex to low frequencies
The basilar membrane is tonotopically organized: narrow and stiff at the base for high frequencies, wide and flexible at the apex for low frequencies.
The basilar membrane width increases approximately 5-fold from base to apex while stiffness decreases about 100-fold. This explains why noise damage to the basal region preferentially affects high-frequency hearing.
Question 6: What is the function of the Eustachian tube?
- To equalize air pressure between the middle ear cavity and atmospheric pressure (Correct answer)
- To transmit sound vibrations from outer to inner ear
- To produce cerebrospinal fluid for the inner ear
- To protect the cochlea from excessive noise
Correct answer: To equalize air pressure between the middle ear cavity and atmospheric pressure
The Eustachian tube connects the middle ear to the nasopharynx and opens during swallowing and yawning to equalize pressure.
Pressure equalization across the tympanic membrane is essential for proper vibration and sound transmission. Eustachian tube dysfunction can cause negative middle ear pressure, fluid accumulation, and conductive hearing loss.
CAOHC Physics of Sound and Anatomy 2
What is the function of the ossicular chain in the middle ear?