Which structure in the inner ear converts sounds into nerve impulses for the brain?

The cochlea is the correct answer because it plays a crucial role in the process of hearing. Within the cochlea, there are specialized hair cells that detect sound vibrations. When sound waves travel through the fluid-filled chambers of the cochlea, they cause the hair cells to move. This movement generates electrical impulses that are then transmitted to the auditory nerve and sent to the brain for interpretation.

Understanding the other structures provides additional context. The auditory nerve is important for transmitting the impulses from the cochlea to the brain but does not convert sounds itself; rather, it is the pathway for the signals after conversion occurs in the cochlea. The semicircular canals are involved in balance rather than hearing, detecting changes in head position and movement, which is essential for maintaining equilibrium. The Eustachian tube serves to equalize pressure between the middle ear and the atmosphere and does not play a direct role in sound transduction. This highlights the specific and fundamental function of the cochlea in the hearing process.