Ear: Sound & Balance
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Transcript of Ear: Sound & Balance
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Ear: Sound & Balance
Sensory System
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Outer Ear: Auricle• Called the Pinna
– Fx: Collects sound waves–Visible part of the ear, outside the head
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Outer Ear: External Auditory Canal
• Extends from Pinna to eardrum– Fx: Transmits sound waves
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Outer Ear: External Auditory Canal
• Produces Cerumen (earwax)–Fx: Traps foreign bodies
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Middle Ear:• Air-filled• Converts sound waves to mechanical energy
• Amplifies it• Conducts to next chamber
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Components:• Tympanic membrane – Eardrum– Vibrates– Sound toMechanical
Energy
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Perforated Eardrum:
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Otitis Media
• Inflammation of the middle ear
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Components:• Ossicles – 3 bones
– Malleus (Hammer)– Incus (Anvil)– Stapes (Stirrup)
• Fx: Mechanical vibration
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Middle Ear:• Oval window - Tranfers mechanical vibration from middle ear to inner ear
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View of OVAL WINDOW
Oval Window
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Eustachian Tube
Fx:• Adjusts pressures between middle
ear & outside• Drains middle ear
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Eustachian Canal • Normally closed• Swallowing & yawning open it• Tympanic membrane will not
vibrate well if pressures not equal
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Eustachian Canal • If fail to open, increased
pressure (pain) and infections
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Requires Ear Tubes – drain the excess fluid & prevent infection
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Inner Ear
• Bony Chambers (fluid-filled)•Vestibule•Semicircular Canals•Cochlea
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Inner Ear Bony Labyrinth
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Inner Ear Bony Labyrinth
• Fluid-filled = Perilymph • Membranous sac is
suspended in the periliymph = Membranous labyrinth
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Inner Ear Membranous Labyrinth
• Sac contains thick fluid = Endolymph
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Hearing and the Inner Ear
- Cochlea
• Snail-like shape• Membranous sac contains organ of Corti
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Cochlear DuctsPerilymph
Membranous labyrinth
EndolymphOrgan of Corti
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Organ of Corti• Contains specialized hearing
receptors or hair cells• Embedded in basilar
membrane
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Organ of Corti
• Hair cells covered by gel membrane (Tectorial membrane)
• Corti converts mechanical energy into electrochemical energy
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Hearing Process
• Ossicles vibrate oval window
• Sets the fluids into motion (pressure waves)
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Hearing Process
• Vibrate basilar membrane
• Hair cells rub tectorial membrane (bent)
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Hearing Process
• Hair cells transmit impulse to cochlear nerve
• Interpretation of sound in temporal lobe
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Sound Energy to Hearing Interpretation
Sound Energy Mechanical Energy
Mechanical Electrochemical
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Balance: Static Equilibrium
• Position of head when not moving (which way is up)
• Membranous sacs in vestibule contain maculae
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Maculae Physiology• As head moves,
otoliths roll in response to gravity
• Pulls on gel and bends hairs in receptors
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Maculae Physiology• Hair cells send impulse via
vestibular nerve
• Signal to cerebellum for interpretation
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Balance: Dynamic Equilibrium
• Rotation of head or movement is detected
• Membranous semicircular canals filled with endolymph
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Crista Ampullaris• Membranous semicircular
canals contain crista ampullaris
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Crista Ampullaris• Contains receptor cells (w/
hairs) embedded in cupula (gel-like cap)
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Ampullaris Physiology• When head moves,
endolymph lags behind
• Cupula drags against endolymph current and bends hairs
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Ampullaris Physiology• Stimulates hair cells to send
impulse
• Vestibular nerve sends impulse to cerebellum