When the stapes footplate moves inward during sound transmission, pressure waves enter the scala vestibuli. The displacement that allows this movement to occur at the opposite end of the scala media system is produced by the:

• A Oval window membrane bulging outward
• B Basilar membrane bowing toward the scala vestibuli
• C Endolymphatic sac expanding into the posterior cranial fossa
• D Secondary tympanic membrane bulging into the middle ear ✓

Explanation

The round window is closed by the secondary tympanic membrane, the only soft tissue seal between the scala tympani and the middle ear. When the stapes drives perilymph inward at the oval window, this membrane bulges outward into the middle ear, dissipating pressure and permitting wave travel. If it becomes fixed or obstructed, as in otosclerosis involving the round window niche, a conductive hearing loss results despite a mobile footplate.

Reference: Dhingra's Diseases of Ear, Nose and Throat, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.