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23 Cards in this Set
- Front
- Back
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How is sound transduced to motion?
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External ear focuses sound to tympanic membrane
Tympanic membrane connects to middle ear ossicles, transducing motion from the sound throughout ossicles |
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The _____ collects & enhances sound in a directional manner (front)
What does this allow? |
auricle
localization of sound source w/ one ear= monaural localization |
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The middle ear (ossicles, tympanic membrane, eustachian tube) converts sound to motion in the ________ & then into ______________ in the fluid of the inner ear
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motion
sound waves (sound waves measured in freq (CPS, Hz) & volume (decibels) |
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How does the middle ear provide amplification?
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based on comparison of the footplate of the stapes to the oval window (22:1)
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Neural reflex sound dampening is mediated through the connection of what muscles to the ossicles?
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tensor tympani (CN V)- to the malleus
stapedius muscle (CN VII)- to the stapes |
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The inner ear contains both the auditory and vestibular sensory apparatus in the _________ bone
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(petros portion) temporal bone.
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The bony labyrinth contains _________
The membranous labyrinth contains _______ What do these fluids contribute to? |
perilymph
endolymph contribute to sound transduction to APs w/i cochlea |
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The _______ is the auditory component of both the bony & membranous labyrinth
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cochlea
(membranous= cochlear duct= blind ended tube of cochlea) |
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The pressure waves generated by the _____________ are abated at the __________________.
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stapes in the oval window (scala vestibuli compartment)
round window (scala tympani) |
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Endolymph in the membranous labyrinth is secreted by the ____________ & is similar to intracellular fluid, relatively high in ___ & low in ___.
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stria vascularis
high in K+ & low in Na+. *NOTE: perilymph is similar to CSF |
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__________ is the site of transduction of sound waves into APs. It is a complex epithelium on the basilar membrane that is continuous along the spiral of the cochlea.
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The organ of Corti
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The organ of Corti contains _________, that contact dendrites of neurons in the spiral ganglia.
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hair cells
(two types in rows, 1 inner & 3 outer, extend all the way up the cochlea) |
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The hair cells contain _____ that contact the tectorial membrane
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stereocilia
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Describe the conversion of sound waves to electric potentials.
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1. Sound waves in the cochlear fluid cause a movement of the stereocilia leading to depolarization of the hair cells (=mechanoelectrical transduction)
2. The depolarization produces a Ca++ based release of neurotransmitter at synapses on spiral ganglion cell dendrites |
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Hair cell depolarization varies on sound & can be measured throughout the cochlea. What does this produce?
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cochlear microphonic
(= assess cochlear fxn) |
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How is the electrical potential in hair cells supported?
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by diff ion concentrations in endlymph & perilymph
= apical & soma compartments of hair cell contact diff fluids/diff extracellular ion concentration (*diff necessary for hair cell fxn) |
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Describe place theory
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Hair cells near the base of the cochlea/basilar membrane are activated by high freq, while hair cells near the apex are activated by low freq--> tonotopic organization of sound
(used for auditory neural pathways) |
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Hearing sensitivity is greatest in the range of normal speech (2000-4,000 Hz)
What is the normal hearing frequency range? |
50 to 16,000 Hz, in children 20 -20,000 Hz
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Decibels characterize volume as 1-2 db is barely detectable,
normal conversation 60 db, sounds above ________ can elicit pain and cause damage to hearing. |
120-130 db
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In the spiral ganglia,how is tonotopic organization maintained?
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Diff neurons have diff threshold frequencies to produce APs
(neurons also produce initial bursts of activity = alerting fxn) |
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How is sound volume coded?
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by the dynamic range of individual spiral ganglion neurons & the type of neurons responding
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What are the 2 types of sensory neurons in the spiral ganglia
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type I:
90% afferent innervation of hair cells on inner hair cells (freq detectors) each innervates 1-2 hair cells many neurons may also innervate same cell (& have diff freq) type II: efferent innervation from olivocochlear bundle (contractile properties= auditory sharpening) on outer hair cells (sound detection) innervate multiple cells low threshold, less freq specific |
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Cochlea can also be stimulated through sound conduction through bone. Why is this important?
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Independent of external & middle ear--> can distinguish btwn neural & mechanical damage to cochlea
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