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39 Cards in this Set
- Front
- Back
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What are the 2 types of hearing loss?
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1. Conductive - blockage of sound in conducting path from source to cochlea
2. Sensorineural - damage to inner ear or central-auditory pathway |
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Conductive disorders are principally found where?
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Middle Ear
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Sensorineural hearing loss usually arises where?
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Cochlea and involves damage or loss of hair cells and auditory nerve connection
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What is presbycusis?
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Age related hearing loss - most marked at HIGH frequency
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What are the 3 bones of the middle ear?
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1. Maleus
2. Incus 3. Stapes |
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Why do we need a middle ear?
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Recall pool analogy.
Amplifies the energy that was reflected as sound goes from air to water |
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What is the membrane that separates the middle ear from the outer ear?
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Tympanic membrane
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The vibrational input from the stapes footplate is into where?
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Scala vestibuli
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The sensory structure of the inner ear is what?
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The organ of corti
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The scala media is filled with what?
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Endolymph - filtrate of CSF
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The scala vestibuli is filled with what?
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perilymph
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The ionic gradients between the endolypmh and perilymph generate what?
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+80mV positive voltage in scala media
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What is the "business end" of the cochlea?
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Scala media
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What cells bring efferents to the ear from brain?
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Outer hair cells
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What cells bring afferents from the ear to the brain?
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Inner hair cells
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What is the organization of hair cells in the organ of corti?
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- Single row of inner hair cells
- Three rows of outer hair cells |
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What are the characteristics of the auditory nerve axons synapsing with inner hair cells?
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1. 35,000 Type 1 afferents
2. 8-12 afferents per IHC 3. Mylenated |
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What are the characteristics of the auiditory nerve axons synapsing with outer hair cells?
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1. 800 Type II afferents
2. 1 afferent per OHC 3. Each innervates ~ 14 OHCs 4. Unmylinated |
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Hair cell cilia are connected via what?
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Tip-links
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What is the gating spring hypothesis of hair cell transduction?
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Cilia pulled in one direction causes ion channels to open
Cilia pushed in other direction closes ion channels |
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How do hair bundles get stimulated?
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Deflections in the basilar membrane causes pressure waves in fluid of inner ear, these deflections cause movements/stimulation of hair bundles
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High frequency sounds elicit vibrations where in the basilar membrane?
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BASE
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Low frequency sounds elicit vibrations where in the basilar membrane?
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APEX
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Movement of the basilar membrane in what direction causes tilting of sterovilli that opens transduction channels?
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Upward Movement
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In inner hair cells, depolarization causes what?
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NT release
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In outer hair cells, depolarization causes what?
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Contraction of PRESTIN
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What is the pattern of membrane depolarization at low frequency sounds?
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Membrane follows periodic motions of the sensory hairs
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What is the pattern of membrane depolarization at high frequency sounds?
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Membrane depolarization is constant
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What is one of the main roles of the inner ear in terms of complex sound?
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Perform spectral decomposition - breakdown complex sound into different frequencies.
And represent these frequencies at distinct locations along the tonotopically organized organ on corti |
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Overall, how is pitch/frequency encoded in the ear?
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Labeled Line
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What is the periodicity principle of frequency coding?
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Output of a single inner hair cell is encoded by MULTIPLE neurons synapsing on an IHC
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Are the characteristics of the HC's different in different locations of the basilar membrane?
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NO, they are all the same
Different properties of the BASILAR MEMBRANE gives rise to differences in tuning |
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In presbiscus, where is the progression of damage?
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Loss of HC's from BASE (high freq) to the APEX (low freq) of the basilar membrane
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In presbiscus, is there any nerve damage?
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NO, ONLY HC's
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Sharpness of the type I afferent tuning curves is dependent on what?
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Outer Hair cells
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How is intensity of sound encoded?
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By the NUMBER of AP's
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How can a single HC encode/cover such a wide range of intensities?
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Different afferent neurons carry a subset of optimal ranges
Their ensemble allows for full range to be covered |
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Large synapses on the IHC cover what level of intensities?
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small
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Small synapses on the IHC covere what level of intensities?
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LOUD!
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