The Cochlea to brain transmission system.
The Cochlea to brain transmission system contains 30000 nerve fibres coming from the organ of Corti to form the auditory nerve. The fibres are grouped by the frequency of the sound signal they carry, the number of fibres a sound requires gives the brain a gauge of its intensity.

Coming from the brain, descending nerve fibres may carry instructions from the brain back to the ear to filter out and thus eliminate some signals which the brain determines are of no importance, and concentrate on others. After passing through the cochlear nucleus, some of the descending nerves from the brain go to the middle ear where they control the muscles used for fending off dangerously loud sound.

The nerve fibres carrying sound signals lead to different parts of the auditory cortex depending on the frequencies they carry. The auditory cortex lies in a deep furrow called the Sylvian fossa. The high tones terminate deep within the Sylvian fossa while the low tones end near the outer surface.

In traditional Chinese medicine, "The Kidneys open into the ear" ... There is a close relationship between the Kidneys and the ears. As Nei Jing says "The Kidney Qi goes through the ear; if the Kidney is harmonised, the ear can hear the five tones" Many hearing problems are treated through the Kidneys. The poor hearing common in the elderly, for example, is a consequence of weakened Kidney Jing.