The inner ear
The inner ear, or cochlear, is a snail-shaped organ. One end of this organ is the balance mechanism, and the other is for hearing. The inner ear is the beginning of the ear's electrical system, or the auditory nerve system. The inner ear works similarly to a microphone. A microphone very simply takes the physical vibration of sound into one end, and turns that vibration into an electrical signal that passes out the wire at the bottom of the microphone. The inner ear does much the same thing. The inner ear contains about 30,000 or so tiny hair cells. Each time the vibration of sound causes one or more of these hair cells to move, a signal is sent to the brain telling it that a sound has occurred. Each hair cell responds to a slightly different frequency. The inner ear contains both mechanical and electrical components, but is essentially the beginning of the nerve pathway, so it is generally considered part of the "sensorineural" components rather than the "conductive" system.

The brain
The brain is very much a part of our ear, or auditory system. The brain is the organ that takes all of the auditory information gathered and processed by the outer ear, the middle ear, and the eighth nerve, and interprets it in such as way that we are able to glean useful information relating to all aspects of sound, whether it be a simple environmental sound, or complex sounds such as music or speech.

The eighth nerve
The eighth nerve, or auditory nerve, is quite a complex and sophisticated structure. For the purposes of our discussion, we can consider it as the "wire" that connects the output of the inner ear to the brain.