1. Outer ear

2. Middle ear

3. Inner ear

4. Acoustic nerve

5. Brain' s auditory processing centers.

The outer ear consists of the pinna, or auricle and the ear canal. The pinna serves as a collector of sound vibrations around us and funnels the vibrations into the ear canal. It assists us in determining the direction and source of sound.  The ear canal is about an inch long and ¼ inch in diameter. It extends from the pinna to the eardrum. The ear canal contains hairs and wax, which help to prevent foreign bodies, such as insects or dust, from entering the ear canal.

The middle ear begins with the eardrum at the end of the ear canal. The middle ear contains three tiny bones called the ossicles. These three bones form a connection from the eardrum to the inner ear. As sound waves hit the eardrum, it moves back and forth causing the ossicles to move. Also, in the middle ear is a tube called the eustachian tube. It runs from the front wall of the middle ear down to the back of the nose and throat. This tube provides ventilation and access to outside air and equalizes air pressure on both sides of the eardrum.

The inner ear contains the sensory organs for hearing and balance. The cochlea is the hearing part of the inner ear. The semicircular canals , the utricle and the saccule are the balance part of the inner ear. The cochlea is a bony structure shaped like a snail and filled with fluid and a sensory receptor which holds the hair cells, the nerve receptors for hearing.

The mechanical energy from movement of the middle ear bones pushes in the cochlea. This force moves the cochlea's fluids that, in turn, stimulate tiny hair cells. Individual hair cells respond to specific sound frequencies (pitches) so that, depending on the pitch (frequency) of the sound, only certain hair cells are stimulated.

Signals from these hair cells are translated into nerve impulses. The acoustic nerve (VIII cranial nerve) transmits these nerve impulses to the brain for processing of the information in the central auditory system.