Which organ vibrates in response to sound waves and has tiny sensitive hairs connected to nerve fibers?

The correct answer is the cochlea, which is the part of the inner ear responsible for converting sound waves into nervous impulses that the brain interprets as sound. The cochlea is a spiral-shaped organ filled with fluid and has tiny hair cells that play a crucial role in hearing. When sound waves enter the cochlea, they cause the fluid inside to move, which in turn causes these delicate hair cells to vibrate. The movement of the hair cells generates nerve impulses that travel through the auditory nerve to the brain, where the sound is processed.

The auditory cortex is not involved in the physical vibration in response to sound waves; rather, it is part of the brain where auditory information is processed after it has been converted into nerve signals. The structure known as the organ of Corti is found within the cochlea and contains the hair cells, but it is not the part that vibrates in response to sound waves itself. Lastly, the semicircular canals are involved in balance and spatial orientation, not in the processing of sound.