Concept: This question tests your understanding of the mechanism of hearing, specifically the process of auditory signal transduction within the cochlea.

Why (A) is correct: When sound waves cause vibrations in the fluid of the cochlea, the basilar membrane moves. This movement causes the hair cells (specifically their stereocilia) embedded in the basilar membrane to bend against the stationary tectorial membrane. This bending opens ion channels, leading to depolarization and the generation of nerve impulses.

Why other options are wrong:

(B) Pressure waves on the oval window cause vibrations of the malleus (incorrect order, malleus is before oval window) and are transferred via the stapes to the oval window, not the round window (round window dissipates pressure).

(C) Movement of the stapes causes oscillations in the perilymph of the cochlea, not the tympanic membrane (tympanic membrane vibrates first) or endolymph directly.

(D) Oscillations of the stapes against the oval window set up pressure waves in the perilymph of the cochlea, not the semicircular canals (semicircular canals are for balance).

Common Mistake: Students often confuse the roles of the oval window and round window, or the specific membranes involved (basilar vs. tectorial) and their interaction with hair cells.

NEET Tip / Mnemonic: Remember the sequence of sound transmission: Ear Drum (tympanic membrane) → Malleus → Incus → Stapes → Oval Window → Cochlea (fluid movement) → Basilar membrane → Hair cells (stereocilia bend against tectorial membrane) → Nerve impulse. (ED MISOC BHN - a bit clunky, but covers the main steps!)

Correct Answer: (A)