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Outer/External Ear
The external ear consists of the pinna (ear lobe), ear canal, and the outer layer of the tympanic membrane (ear drum). The pinna acts to protect the tympanic membrane while also acting as a funnel to collect sound. Sound enters the outer with help from the pinna and then enters the ear canal. At the eardrum, sound energy (air pressure changes) are transformed into mechanical energy of eardrum movement.
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Middle Ear
The middle ear, separated from the external ear by the eardrum (tympanic membrane), is an air-filled cavity (tympanic cavity). It connects to the throat via the eustachian tube. Having this ear-throat connection makes the ear susceptible to ear infection (otitis media). In infants and small children, this tube lies horizontal instead of more vertical (as seen in older children/adults). The horizontal placement of the eustachian tube makes it more difficult to drain fluid, which leads to ear infections more likely. The eustachian tube functions to equalize air pressure on both sides of the eardrum. Elevated levels distorts the ear pressure in our ears, which is why chewing gum (by helping to open up the eustachian tube) often helps to relieve the extra build-up of this pressure.
Adjoining the eardrum are three linked, movable bones called "ossicles," which convert sound waves after striking the eardrum into mechanical vibrations. The smallest bones in the human body, the ossicles are named for their shape. The malleus (hammer) joins the inside of the eardrum. The incus (anvil), the middle bone, connects to the malleus and to the stapes (stirrup). The base of the stapes, the footplate, fills the oval window which leads to the inner ear.
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Inner Ear
The inner ear consists of the cochlea, semi-circular canals, and the auditory nerve. The organs for both hearing and balance are found here in the inner ear. The inner ear is filled with fluid. The cochlea is considered the main sensory organ for hearing. The semicircular canals are responsible for maintaining equilibrium and balance. Electrical impulses from the cochlea (the hair cells in the cochlea) trigger nerve impulses in the auditory nerve. The auditory nerve transmits the neural impulses to the auditory centers of the brain where sound is finally perceived.
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