How do we hear?

Sound waves travel into the ear canal until they reach the eardrum. The eardrum passes the vibrations through the middle ear bones or ossicles into the inner ear. The inner ear is shaped like a snail and is also called the cochlea. Inside the cochlea, there are thousands of tiny hair cells. Hair cells change the vibrations into electrical signals that are sent to the brain through the hearing nerve. The brain tells you that you are hearing a sound and what that sound is.

Take a look inside your ear!
Anatomy and Physiology Flash activity

Each hair cell has a small patch of stereocilia sticking up out of the top it. Sound makes the stereocilia rock back and forth. If the sound is too loud, the stereocilia can be bent or broken. This will cause the hair cell to die and it can no longer send sound signals to the brain. In people, once a hair cell dies, it will never grow back. The high frequency hair cells are most easily damaged so people with hearing loss from loud sounds often have problems hearing high pitched things like crickets or birds chirping.

Hair cell pictures taken with an electron microscope:

Single Hair Cell:
No, this is not a pickle on fire. It is a picture of one, tiny hair cell. Each ear has about 18,000 hair cells in it and all of them could fit on the head of a pin. This picture was taken with a confocal microscope. The green part is called the cell body. The yellow and red parts on top are the stereocilia.
Normal Hair Cells:
This is a picture of the top of a healthy hair cell. The stereocilia are standing in perfect rows.
Damaged Hair Cells:
This is a picture of the top of a hair cell that has been in very loud noise. Look at what happened to the stereocilia! They are all bent over. This hair cell will die and never send signals to the brain again. This is a cause of hearing loss and can cause tinnitus (ringing in the ears).