What happens when sound waves reach the cochlea?

What happens when sound waves reach the cochlea?

• A. They bend hair cells on the basilar membrane outside the cochlea.
• B. They trigger action potentials directly in the auditory cortex.
• C. They cause pressure waves in the fluid of the scala vestibuli and scala tympani.
• D. They cause the eardrum to ossify.

Answer: (C)

When sound reaches the cochlea, the stapes at the oval window pushes on the inner ear fluids to create pressure waves in the perilymph of the scala vestibuli. These waves pass around the cochlear partition into the scala tympani, moving the basilar membrane. That mechanical motion deflects the hair cell stereocilia on the organ of Corti, producing receptor potentials and triggering auditory nerve impulses that travel to the brain. The basilar membrane’s movement pattern encodes pitch, so different frequencies stimulate different regions. The other statements don’t fit because hair cells bend on the cochlear partition itself, not outside it; action potentials begin in the auditory nerve and brainstem, not directly in the cortex; and the eardrum does not ossify.

When sound reaches the cochlea, the stapes at the oval window pushes on the inner ear fluids to create pressure waves in the perilymph of the scala vestibuli. These waves pass around the cochlear partition into the scala tympani, moving the basilar membrane. That mechanical motion deflects the hair cell stereocilia on the organ of Corti, producing receptor potentials and triggering auditory nerve impulses that travel to the brain. The basilar membrane’s movement pattern encodes pitch, so different frequencies stimulate different regions. The other statements don’t fit because hair cells bend on the cochlear partition itself, not outside it; action potentials begin in the auditory nerve and brainstem, not directly in the cortex; and the eardrum does not ossify.