ANATOMY AND
PHYSIOLOGY OF THE EAR
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Main Components of the
Hearing Mechanism
 Outer Ear
 Middle Ear
 Inner Ear
 Central Auditory Nervous System
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Structures of the Outer Ear
 Auricle (Pinna)
– Collects sound
– Helps in sound localization
– Most efficient in directing high frequency sounds to the eardrum
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External Auditory Canal
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Approximately 1¼ inch in length
“S” shaped
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Lined with cerumen glands
Outer 1/3rd cartilage; inner
2/3rds mastoid bone
Increases sound pressure at the tympanic membrane by as much as 5-6 dB (due to acoustic resonance)
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Mastoid Process
 Bony ridge behind the auricle
 Provides support to the external ear and posterior wall of the middle ear cavity
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Tympanic Membrane
 Thin membrane
 Forms boundary between outer and middle ear
 Vibrates in response to sound
 Changes acoustical energy into mechanical energy
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 A: Malleus
 B: Incus
 C: Stapes
– Ossicles are smallest bones in the body
– Act as a lever system
– Footplate of stapes enters oval window of the cochlea
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 Lined with mucous membrane; connects middle ear to back of the throat
(nasopharynx)
 Equalizes air pressure
 Normally closed except during yawning or swallowing
 Not a part of the hearing process
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Stapedius Muscle
 Connects the stapes to the middle ear wall
 Contracts in response to loud sounds; known as the Acoustic Reflex
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 Cochlea - Snail-shaped organ with a series of fluidfilled tunnels; converts mechanical energy into electrical energy
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Structures of the Inner Ear (Cont.)
 Oval Window – located at the footplate of the stapes; when the footplate vibrates, the cochlear fluid is set into motion
 Round Window
– functions as the pressure relief port for the fluid set into motion initially by the movement of the stapes in the oval window
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Organ of Corti
 The end organ of hearing; contains stereocilia and hair cells.
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Frequency-specific
High pitch sounds = base of cochlea
Low pitch sounds = apex of cochlea
When the basilar membrane moves, a shearing action between the tectorial membrane and the organ of Corti causes hair cells to bend
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 Consists of three semicircular canals
 Shares fluid with the cochlea
 Controls balance
 No part in hearing process
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Central Auditory System

8th Cranial Nerve or “Auditory Nerve” carries signals from cochlea to brain
 Fibers of the auditory nerve are present in the hair cells of the inner ear
 Auditory Cortex: Temporal lobe of the brain where sound is perceived and analyzed
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How Sound Travels Through
The Ear...
Acoustic energy , in the form of sound waves, is channeled into the ear canal by the pinna . Sound waves strike the tympanic membrane, causing it to vibrate like a drum, and changing it into mechanical energy . The malleus , which is attached to the tympanic membrane, starts the ossicles into motion. (The middle ear components mechanically amplify sound). The stapes moves in and out of the oval window of the cochlea creating a fluid motion. The fluid movement within the cochlea causes membranes in the Organ of Corti to shear against the hair cells . This creates an electrical signal which is sent via the Auditory Nerve to the brain, where sound is interpreted!
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QUESTIONS?
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