The cochlea is a coiled, bony, fluid-filled tube in the inner ear; what triggers nerve impulses there?

The cochlea is a coiled, bony, fluid-filled tube in the inner ear; what triggers nerve impulses there?

• A. Sound waves traveling through the cochlear fluid
• B. Air vibrations hitting the eardrum
• C. Bones in the middle ear directly stimulating nerves
• D. Hair cells alone without fluid movement

Answer: (A)

The key idea is that nerve impulses in the cochlea come from the mechanical energy of sound being converted into a signal by the hair cells through movement of cochlear fluid. When sound waves enter the inner ear, they set the eardrum and then the middle-ear bones vibrating. Those vibrations push on the oval window, creating pressure waves in the fluid of the cochlea. As these waves move along the fluid, they cause the basilar membrane to vibrate at specific spots depending on the sound’s frequency. The hair cells sitting on the basilar membrane have stereocilia that bend in response to this movement, which opens ion channels, leading to receptor potentials and release of neurotransmitters to the auditory nerve. That neural firing is the actual nerve impulse signal. So, while the initial vibrations set everything in motion, the trigger for neural impulses in the cochlea is the wave motion of cochlear fluid that moves the hair cells and converts mechanical energy into electrical signals. Air hitting the eardrum initiates the process but does not directly trigger impulses in the cochlea. The bones in the middle ear help transmit the force but don’t directly stimulate nerves. Hair cells don’t generate signals without the fluid-driven movement that bends their stereocilia.

The key idea is that nerve impulses in the cochlea come from the mechanical energy of sound being converted into a signal by the hair cells through movement of cochlear fluid. When sound waves enter the inner ear, they set the eardrum and then the middle-ear bones vibrating. Those vibrations push on the oval window, creating pressure waves in the fluid of the cochlea. As these waves move along the fluid, they cause the basilar membrane to vibrate at specific spots depending on the sound’s frequency. The hair cells sitting on the basilar membrane have stereocilia that bend in response to this movement, which opens ion channels, leading to receptor potentials and release of neurotransmitters to the auditory nerve. That neural firing is the actual nerve impulse signal.

So, while the initial vibrations set everything in motion, the trigger for neural impulses in the cochlea is the wave motion of cochlear fluid that moves the hair cells and converts mechanical energy into electrical signals. Air hitting the eardrum initiates the process but does not directly trigger impulses in the cochlea. The bones in the middle ear help transmit the force but don’t directly stimulate nerves. Hair cells don’t generate signals without the fluid-driven movement that bends their stereocilia.