The human ear, as a sound receiver, has to operate under a wide range of conditions. It is subject to sounds of varied complexities, frequency ranges and intensity levels. Almost all noise control measures are established to minimise the possibility of physical damage to the hearing mechanisms of the ear or to maintain acoustical environments which are conducive to adequate speech communication and privacy. The audible frequency range for a normal youth with no hearing loss is from 16 Hz to 20,000 Hz.

Designated as outer ear structures are the visible part of the ear, called the auricle, and the waxy, dirt-trapping auditory canal which conveys changes in air pressure and sound waves to the eardrum. The eardrum, or tympanic membrane, begins the middle ear, which also comprises the eustachian tube and the three vibrating bones of the ear: malleus, incus, and stapes. The cochlea and semicircular canals make up the inner ear. Information passes from the inner ear to the brain via the auditory nerve.

Apical Turn

The final turn in the spiral of the cochlea furthest from the oval and round windows. It contains that part of the organ of Corti which responds to low frequencies.

Auditory Nerve

There are around 30,000 nerve fibres to the brain.

The data rate is around 100 Kbit/sec.

Basilar Membrane

A membrane inside the cochlea that vibrates in response to sound, exciting the hair cells.


A snail shaped mechanism in the inner ear that contain hair cells of basilar membrane that vibrate to aid in frequency recognition.

Ear Canal

The external auditory meatus; the canal between the pinna and the eardrum.


The tympanic membrane located at the end of the ear canal that is attached to the ossicles of the middle ear.

Eustachian Tube

The tube running from the middle ear into the pharynx that equalizes middle-ear and atmospheric pressure.

External Meatus

The ear canal terminated by the eardrum.

Hair Cells

Sensory cells in the cochlea which transform the mechanical energy of sound into nerve impulses.

Each ear has 23,500 hairs in the cochlea.

Inner Ear

The inner ear is a labyrinth of twisting fluid-filled passages associated with hearing and balance. Three canals wind into a snail-shaped structure called the cochlea. Sound vibrations amplified by the bones of the middle ear travel through these canals, which in turn causes tiny hairs to to move. When these hairs rub against each other they push on protein molecules protruding from the surfaces of each hair. The molecule then acts as a lever, opening a channel, known as an ion gate, inside the hair and so allowing potassium ions to flow from the top of the hair into the cells at its root. This flow of ions triggers an electrical signal which the brain interprets as sound. At the base of each level is a molecular spring which returns the lever to its original position, ready to detect the next vibration. Sounds from the outside are in this way encoded to travel to the brain. The rear section of the inner ear houses the semicircular canals. Connected to each other by the structure called the vestibule, the canals are sensitive to gravity, acceleration, and head movement and position.

Middle Ear

The cavity between the eardrum and the cochlea housing the ossicles connecting the eardrum to the oval window of the cochlea.


A linkage of three tiny bones providing the mechanical coupling between the eardrum and the oval window of the cochlea consisting of the hammer, anvil, and stirrup.

Oval Window

A tiny membranous window on the cochlea to which the foot plate of the stirrup ossicle is attached. The sound from the eardrum is transmitted to the fluid of the inner ear through the oval window.


The exterior part of the ear. The ridges are important in determining the direction sound comes from.

Round Window

The tiny membrane of the cochlea that opens in the middle ear that serves as a "pressure release" for the cochlear fluid.

Semicircular Canals

The three sensory organs for balance that are a part of the cochlear structure.

See also: Acoustic Source Location, Aero-Otitis Media, Eye, Hearing, Hearing Damage, Hearing Range in Animals, Knudson′s Law, Otologist, Psychoacoustics, Smell, Sonic, Sound, Temporary Threshold Shift, Tinnitus.

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Subjects: Audio Medical

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