Download The Ear and Hearing 1. Outer Ear

1. Outer Ear- main purpose is to funnel sound
waves to inner ear.
1a. Auricle-gathers sound waves
1b. External acoustic meatus- transmits sound waves to
tympanic membrane
1c. Tympanic membrane (eardrum)-amplifies sound and
transmits it to middle ear.
2. Middle Ear (tympanic cavity)- main purpose is to
transmit sound waves through movement and
vibration of the ossicles (bones) to the inner ear.
2a. Malleus-receives sound waves from eardrum
2b. Incus-transmits sound waves to stapes
2c. Stapes-transmits sound waves to oval window
2d. Auditory tube (Eustachian tube)-connects
middle ear to throat and helps maintain air
pressure
2e. Tympanic cavity- air filled cavity that connects
to the auditory tube
Fig10.07
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Incus
Malleus
Stapes
© The McGraw-Hill Companies, Inc./Jim Womack, photographer
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3. Inner Ear- major purpose is to generate movement of
tiny hair like cells with a fluid called endolymph
and perilymph to transmit impulses to the brain
through nerves.
3a. Oval window -receives amplified sounds waves
from stapes.
3b. Round window-opening to inner ear, moves
opposite oval window to ensure fluid moves in
cochlea.
3c. Cochlea-hearing, hair cells detect frequency of
sound
3d. Cochlear nerve -sends information about sound
to brain
3e. Vestibular nerve -sends information about the
heads position to brain
3f. Vestibule-detects static equilibrium (the position
of the head when still)
3g. Semicircular canals -detect dynamic equilibrium
(motion of head) and aids in balance
Fig10.08
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Osseous labyrinth
Perilymph
Membranous labyrinth
Endolymph
Osseous labyrinth
(contains perilymph)
Membranous labyrinth
(contains endolymph)
Semicircular
canals
Utricle
Vestibular nerve
Saccule
Cochlear nerve
Scala
chambers (cut)
containing
perilymph
Cochlear
duct (cut)
containing
endolymph
Ampullae
Oval
window
Round Maculae
window
Cochlea
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Video Links
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How Hearing Works
Conductive Hearing Loss
Sensorineural Hearing Loss
Cochlear Implants
I. HOW WE HEAR
A. The outer ear- funnels sound waves of a given
frequency (measured in hertz) and intensity
(measured in decibels) to the tympanic membrane,
causing it to vibrate.
B. Vibration of the tympanic membrane causes
vibrations in the middle ear ossicles(tiny bones)malleus, incus and stapes, which vibrates the oval
window of the cochlea.
C. Vibration of the oval window sets up a traveling
wave of perilymph in the vestibule of the inner ear.
The wave passes through the cochlear duct- filled
with endolymph.
D. The sensory structure of the cochlea is called the
organ of Corti.
1. Organ of Corti- consists of sensory hair cells on
the basilar membrane. The hair cells send
messages to vestibulocochlear nerve when
stimulated.
2. High frequency sounds- cause maximal
displacement of the basilar membranecloser to its base near the stapes.
3. Low frequency sounds- produce maximal
displacement of the basilar membrane closer to
its apex.
4. Pitch discrimination -- depends on the region
of the basilar membrane that vibrates
maximally to sounds of different frequency.
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Conductive hearing loss -something is
inhibiting the sound waves from
reaching the inner ear
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Malformation of outer ear, ear canal, or middle ear structures.
Fluid in the middle ear from colds.
Ear infection.
Allergies.
Poor Eustachian tube function.
Perforated eardrum.
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Sensorineural hearing loss -indicates the
malfunction of the inner ear in
conducting the message to the brain.
Exposure to loud noise.
 Head trauma.
 Virus or disease.
 Autoimmune inner ear disease.
 Hearing loss that runs in the family.
 Aging (presbycusis)
 Malformation of the inner ear.
 Meniere's Disease.
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