Explain how sound entering the ear produces action potentials in the auditory nerve. What will be an ideal response?
ANSWER: Sound waves enter the auditory ear canal at the end of which is the tympanic membrane. The
tympanic membrane, or ear drum, vibrates when sound waves strike it. The movement of the
tympanic membrane produces movement of the middle ear bones. The last of these bones, the
stapes is attached to the oval window, which is part of the cochlea of the inner ear. As the
stapes moves it pushes on the oval window membrane, which in turn causes the fluid in the
inner ear to move. As the fluid in the inner ear moves it moves the basilar membrane that is
located inside the cochlea. The transduction of sound waves to action potentials occurs as
hair cells on top of the basilar membrane move as the membrane moves. This movement of
hair cells causes cilia on their surface to bend as the cilia are attached to the tectorial
membrane. This bending opens ionic channels which in turn causes the hair cells to release
neurotransmitters. The neurotransmitter stimulates action potentials in the auditory nerve.
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