Hearing is complex, requiring a series of actions and reactions to work. The process involves many parts of the ear working together to convert sound waves into information the brain understands and interprets as sounds. 

1. Sound waves enter the ear canal and travel toward our eardrums.
   

2. The sound waves cause the eardrum and bones in the middle ear to vibrate.
   

3. Tiny hair cells inside cochlea (inner ear) convert these vibrations into electric impulses/signals that are picked up by the auditory nerve.
   

4. At birth, each normal ear has about 12,000 sensory cells, called hair cells, which sit on a membrane that vibrates in response to incoming sound. Each frequency of a complex sound maximally vibrates the membrane at one location.
   
   Because of this mechanism, we hear different pitches within the sound. A louder sound increases the amplitude of the vibration, so we hear loudness.
   

5. Signals sent to the brain from auditory nerve are then interpreted as sounds.

Once the hair cells in the inner ear are damaged, permanent sensorineural hearing loss occurs. Currently, sensorineural hearing loss cannot be restored in humans.  

For updates about scientific efforts to restore hair cells in human ears, learn about Hearing Health Foundation (HHF)'s Hearing Restoration Project (HRP), an international consortium dedicated to finding a biological cure for hearing loss using three animal models. 

Hearing Health magazine is Hearing Health Foundation (HHF)'s free quarterly publication.