The Ear

Before you can understand the difference between normal and impaired hearing, it's important to know how the ear functions. The following diagram describes basic parts of the ear

The outer part of that ear that we see is called the pinna. Sound waves travel through air from the outer ear, (visible portion) through the ear canal and strike the eardrum, which is paper-thin. This causes the eardrum to vibrate, a motion which is received by the middle ear. 

The important role of the inner ear is to convert the mechanical vibrations that strike the eardrum into electrical impulses, or signals, that are sent along a nerve to the brain to be decoded as sound. The middle ear is made up of three bones, the malleus, incus and the staples. The vibrations of the eardrum push these three bones into a rocking motion. The base of the staples bone transmits the vibrations through the oval window into the fluid-filled cochlea of the inner ear. These vibrations cause waves in the cochlea fluid. Hair cells in this fluid bend as a wave passes and create nerve impulses that the auditory nerve carries to the brain. That signal is recognized as sound.

Hearing loss or impairment is caused by any interruption to the path of sound.

Another part of the ears complex structure is the eustachian tube. This tube extends from the middle ear to the back of the throat. When you yawn or swallow the tube opens and ventilates the space in the middle ear. As a result pressure is equalized between the middle ear and the air around you. Problems with the eustachian tube usually require medical attention.

The next diagram puts all these parts as described above into motion.