Sound travels in waves that hit the external ear and then the eardrum, causing vibrations. From the eardrum, the vibrations become pressure waves in the inner ear. The waves are converted to electrical signals, which travel to the brain stem for processing.
The external auditory canal and the pinna, the essential parts of the inner ear, collect sound waves and channel them to the eardrum. Once the eardrum starts to vibrate, the vibration travels to the stirrup, which is a small bone in the middle of the ear. The stirrup applies pressure to the oval window of the ear, producing waves inside the cochlea, a small organ in the ear shaped like a snail.
The cochlea separates waves into the various frequencies, which is important for the differentiation of sounds in the brain. This allows people hear and digest multiple things at once. The cochlea contains a basilar membrane with hair cells, and different hair cells handle sounds at different frequencies as they convert the vibrations to electrical signals. The signals start agitating the 30,000 fibers within the auditory nerve, each of which captures information about a unique frequency. The auditory nerve carries these signals to the brain stem and then to the auditory cortex, where the brain carries out the final processing.