Chapter 15b Hearing and Equilibrium
Ear anatomy
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external ear
external acoustic canal
tympanic membrane
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middle ear
3 ossicles
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inner ear
• malleus
• incus
• stapes
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cochlea
hearing
vestibule
equilibrium
semicircular canals
equilibrium
HEARING
cochlea anatomy
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cochlear duct
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fluid filled membrane
fluid
endolymph
receptor
Organ of Corti = spiral organ
surrounded by 2 chambers :
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fluid
perilymph
scala vestibuli
contacts oval window
scala tympani
contact round window
Organ of Corti
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= spiral organ
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receptors for hearing
within cochlear duct
basilar membrane
support
hair cells
receptor cells
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stereocilia
extensions into tectorial membrane
tectorial membrane
covers stereocilia ; stationary
Sound
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= alternating zones of high and low pressure
sound is a vibration
waves of vibrating air (or any medium)
physics terms
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frequency
# waves per second
wavelength
distance betw crests
amplitude
height of each wave
pitch = frequency
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hertz (Hz) = cps
20 to 20000 Hz
most sensitive range
• 1500 – 4000 Hz
loudness
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hertz (Hz)
= amplitude
decibels (dB)
0 to 120 dB
0 = threshold
hearing
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GOAL = change sound into action potential
depolarize the receptor cells
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open Na channels
How?
stretch their hair
transmission of sound / vibration
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sound wave (air) vibrates tympanic membrane
3 ossicles amplify the vibration
stapes vibrates the oval window
oval window vibrates perilymph
perilymph vibrates endolymph
endolymph vibrates basilar membrane
basilar membrane vibrates hair cells
excitation of receptor cells
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organ of Corti
basilar membrane vibrates hair cells
stereocilia stretch against tectorial membrane
open K channels
K+ (in endolymph) rushes into cell
hair cells depolarize
hair cells release NT
Pitch
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varied thickness of basilar membrane
responds to different frequency
frequency ~ pitch
multiple pitches possible
specific areas of auditory cortex
Pitch and auditory cortex
auditory processing
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pitch
area of basilar membrane / auditory cortex
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loudness
number of hair cells stimulated
frequency of action potentials
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localization
where is sound coming from
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compares both ears
• intensity
• timing
auditory pathway
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to temporal lobe
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cochlear nerve
spiral ganglion
cochlear nuclei
thalamus
temporal lobe
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to inferior colliculi
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auditory reflex
to cerebellum
problems
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deafness
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conduction deafness
neural deafness
tinnitus
Meniere’s syndrome
hearing loss
tinnitus
vertigo
EQUILIBRIUM
equilibrium anatomy
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Vestibular apparatus = 2 structures :
vestibule
linear equilibrium
(static)
semicircular canals
rotational equilibrium (dynamic)
receptors
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linear acceleration
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utricle
saccule
macula
receptor mechanism
hair cells
receptors
rotational acceleration semicircular ducts
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ampulla
receptor mechanism
hair cells
receptors
macula anatomy
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receptor mechanism in utricle , saccule
hair cells
stereocilia
kinocilium
otoliths
excitation of macula
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position change moves otoliths -
bends sterocilia
toward kinocilium
depolarize
away from kinocilium
hyperpolarize
opposite sides
ampulla anatomy
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receptor mechanism of semicircular ducts
crista ampullaris
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hair cells
cupula
excitation of ampulla
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rotation moves endolymph
endolymph deforms cupula
cupula bends sterocilia depolarize
equilibrium pathway
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hair cells
vestibular nerve
vestibular nuclei
medulla
cerebellum
reflex movement
cerebrum
parietal lobe
conscious awareness of position and movement
equilibrium reflexes
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sensory input from
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vestibular apparatus
proprioception
vision
response
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eye movment
skeletal muscle
esp neck and torso
• vestibulospinal tract
• CN XI
problems
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vertigo
nystagmus
motion sickness
dizziness