- Sound waves are transmitted from the external environment to the cochlea through the middle ear during hearing. The functions of the middle ear in hearing are suggested below:
(A) During the transmission of sound waves through the middle ear, the movement of the head of stapes induces a piston like movement on the oval window.
(B) The tympanic membrane functions as a resonator that reproduces the vibration of sound source.
(C) The sound pressure on the tympanic membrane is increased 1.3 times on the oval window by the lever system of malleus and incus.
(D) The area of tympanic membrane is greater than that of the footplate of stapes, and hence sound pressure on tympanic membrane is increased on oval window.
(E) The contraction of tensor tympant muscle causes the manubrium of the malleus to be pulled outward.
(F) The footplate of the stapes is pulled inward by the contraction of stapedius muscle.
Choose the option with all CORRECT statements
(1) A, B and C (2) B, C and D
(3) C, D and E (4) D, E and F
The middle ear serves as a critical mechanical interface between the external environment and the sensitive inner ear structures. Its functions enable the efficient transmission and amplification of sound waves from the air to the fluid-filled cochlea, ensuring effective hearing.
Functions of the Middle Ear in Sound Transmission
1. Piston-like Movement of Stapes on Oval Window (Statement A)
The stapes, the smallest bone in the body, connects to the oval window of the cochlea. The footplate of the stapes moves in and out in a piston-like fashion, transmitting vibrations from the middle ear to cochlear fluids. This movement initiates pressure waves in the cochlea necessary for hearing.entlecture+1
2. Tympanic Membrane Function (Statement B)
The tympanic membrane (eardrum) acts as a sensitive pressure receiver, converting sound waves entering the ear canal into mechanical vibrations. It functions as a resonator but does not simply reproduce the vibration of the sound source; instead, it dampens and filters some frequencies to optimize transmission.
Thus, calling it a resonator reproducing the source vibration exactly is partially true but oversimplified.anatomy+1
3. Lever System of Ossicles and Sound Pressure Amplification (Statements C and D)
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The lever action of the malleus and incus magnifies the force of vibrations between the tympanic membrane and the stapes footplate.
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The manubrium of malleus is about 1.3 times longer than the long process of the incus, providing a mechanical advantage.
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Additionally, the surface area difference between the large tympanic membrane (about 55 mm²) and the small footplate of the stapes (about 3.2 mm²) concentrates the pressure on the oval window, amplifying it approximately 17 times.
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Together, these mechanisms increase the sound pressure roughly 20–30 times from the tympanic membrane to the oval window, compensating for impedance mismatch between air and cochlear fluids.mechanicsofhearing+2
Therefore, both statements C and D are correct.
4. Middle Ear Muscles: Tensor Tympani and Stapedius (Statements E and F)
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The tensor tympani muscle is attached to the malleus. When it contracts (e.g., during loud sounds or chewing), it pulls the manubrium of the malleus inward (not outward) to reduce tympanic membrane vibration and protect the inner ear.
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The stapedius muscle inserts on the neck of the stapes and when contracted, pulls the stapes away from the oval window, reducing movement and protecting the cochlea from loud noise damage.
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Thus, statements E and F are incorrect as they describe the opposite action.hoerstmagazin+2
Summary of Statements
Statement Content Correct/Incorrect A Stapes movement induces piston-like movement on oval window Correct B Tympanic membrane functions as a resonator reproducing vibration of source Partially Correct C Sound pressure increased 1.3 times by ossicular lever system Correct D Tympanic membrane area greater than stapes footplate, increasing sound pressure Correct E Tensor tympani contraction pulls malleus manubrium outward Incorrect F Stapedius muscle contraction pulls stapes footplate inward Incorrect Correct Option Based on Statements
The option with all correct statements is:
(2) B, C and D
Conclusion
The middle ear plays a vital role in sound transmission and amplification through mechanical leverage and area difference, and the piston-like movements of the stapes transfer vibrations efficiently to the cochlea. Protective muscles modulate ossicular movement but act in directions opposite to that stated in E and F.
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