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20 Cards in this Set
- Front
- Back
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Def of Conductive hearing loss
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Associated with interference of sound transmission in the outer or middle ear
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Def of Sensorineural hearing loss
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Associated with the pathology of the cochlea or CN VIII
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Three characteristics of sound and how we perceive them
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• Frequency - pitch/tone
• Intensity - Loudness • Point of origin - Location |
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Structure and Fxn of the Ear:
• Outer - medium the sound travels in - where sound is focused - where vibrations are produced • Middle ear - Medium sound travels - The goal of the middle ear - how its connected to the nasopharynx - the bones it contains (3) • Inner ear - medium the air travel in - Contains this structure - how vibrations are passed in this region - Signal transduction takes place on this structure |
Structure and Fxn of the Ear:
• Outer - Air - External auditory meatus - Tympanic membrane • Middle ear - Air - Amplify sound - Eustacian tube - Malleus, Incus and Stapes • Inner ear - Fluid (Endolymph and perilymph) - Cochlea - The stapes sits on the oval window of the cochlea and generates pressure waves - Organ of Corti |
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Describe two reasons behind pressure amplification in the middle ear
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1. Size difference btwn the tympanic membrane and the oval window allows for greater force
2. Lever ratios of the ossicular chain. Large movements w/ little force are transformed into small movements w/ greater force produced at the oval window |
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Fluid compartments of the cochlea:
• Name the 3 compartments and the major ion in each • Basilar membrane - compartments it separates - Supports this organ |
Fluid compartments of the cochlea:
• 3 compartments - S. vestibuli and tympani: High in Na+ and Cl- (similar to ECF) - S. media: High on K+ (similar to ICF) • Basilar membrane - It separates the S. media from the S. tympani - Supports the Organ of Corti |
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Describe how sound frequency is encoded in the cochlea
• The relationship w/ the basilar membrane • What the envelope of waves represents • How the basilar membrane and place code relate |
At the base of the cochlea, near the oval window:
- the basilar membrane is narrow and stiff --> detect high frequency At the tip of the cochlea (apex), the basilar membrane is wide and floppy ---> detect low frequencies • The envelope of waves is the sum of the deflections of the basilar membrane at diferent sages of wave travel • The place code is the location a nerve cell encodes for a specific stimulus, such as frequency, and the nerve is most active at that particular frequency. When sound moves along as waves along the basilar membrane, the membrane deflects up and down. The points at which there are maximum deflection indicate the overlying hair cells will be the most activated (are the most sensitive at this frequency) and will produce the highest signal in the underlying afferent neurons. |
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Auditory Signal Transduction:
• 1st step in the process -what traveling waves in the cochlea do • 2nd step in the process • Role of outer hair cells - how the hair cells react to depolarization |
Auditory Signal Transduction:
• Deflection of hair cell stereocilia - they deflect the basilar membrane relative to the tectorial membrane • As long as the deflection is in the direction of the cilia, the 2nd step would be to open ion channels • Amplify sound - Hair cells shorten in response to depolarization, then lengthen at rest |
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Essence of the auditory pathways:
• Which structures are represented by the CNS? (5) • What are the components of these structures (7) • What part of the PNS is represented (1) • Where does CN VIII enter the brain and what is the synaptic target? • Where can a lesion produce along the pathway unilateral hearing loss? |
• It enters at the brain stem at the level of the pontomeduallary jxn and
synapses in the Anterior & Posterior cochlear nuclei • B/c of the extensive cross fiber connections at every level of the auditory system, here is NO lesion along the Auditory pathway that can produce unilateral hearing loss. However lesions can diminish the ability to hear. |
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The primary auditory cortex:
• Brodmann's areas • the gyrus and lobe +area involved • Two types of organization - how frequencies are distributed - Type of iNN seen - how cells in A1 are grouped - from where it receives input and to which layer this input is projected |
The primary auditory cortex:
• 41/42 • Transverse temporal gyrus of Heschl on the superior surface of the Temporal Lobe • Two types of organization 1. Tonotopic - frequencies are distributed along a rostral-caudal axis of A1 > low freq --> rostrally & laterally > high freq --> caudally & medially 2. Columnar Organization - has binaural innervation - the cells are grouped according to their pattern of input from both ears > Columns alternate with one being excited by input from both ears while the next being excited by input from just one ear and inhibited by input from another ear. - receives input from the thalamus in layer 4, where the thalamo-cortical fibers synapse |
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Sound localization of low frequencies:
• its foundation • The mechanism used - how the parameter is detected - The relationship btwn EPSPs and larger signals |
Sound localization of low frequencies:
• based on interaural time differences • The mechanism is Coincidence Detection - Time delay, the parameter, is detected via binaural pathways to the Medial Superior Olive (MSO) - When EPSPs are produced by a neuron of the MSO at the same time by signals arriving from both ears, a larger signal will be produced than if the signals had produced separate EPSPs due to the time delay |
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Sound localization of high frequencies:
• its foundation • what is the sound/acoustic shadow? |
Sound localization of high frequencies:
• based on differences in the sound intensity in the two ears when the sound originates from positions lateral to the midline • It is a barrier, usually produced by the head, that diminishes the sound pressure signal, resulting in the other ear receiving a sound of lower intensity |
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How the NS calculates Amplitude differences:
• The first thing to recognize about sound intensity when the sound source is lateral to the midline - which side experiences a higher sound intensity and how does this affect the activity of both LSOs? • From where does the LSO receive excitatory and inhibitory input? • With both LSOs experiencing different initial Amplitude differences, what are the resulting states of the LSOs? |
How the NS calculates Amplitude differences:
• The sound intensity signal will be larger one one side than the other. This produces asymmetrical activity in the LSOs • Input to LSO - Excitatory: Directly from the ipsilateral sensory input fibers - Inhibitory: Indirectly from Contralateral input fibers via the interneurons of the trapezoid nucleus • Resulting states - One LSO will be excited/depolarized and forward its output to higher regions in the brainstem an cortex - The other LSO will be inhibited/hyperpolarized and send no output signals |
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Two neurological examinations of auditory fxn
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Weber's test and Rinne's test
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Weber's Test
• What it tests • The instrument it uses and where it is placed • What is expected in a normal individual • What is expected with conductive hearing loss • What is expected with sensorineural hearing loss |
Weber's Test
• Lateralization of hearing • Tuning fork, placed in the vertex or forehead • Sound quality is heard equally well in both ears • Sound lateralizes to the ipsilateral/diseased side • Sound lateralizes to the contralateral/normal side |
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Rhinne's test
• What it tests • The instrument it uses and where i is placed • What is expected in a normal individual • What is expected with conductive hearing loss • What is expected with sensorineural hearing loss |
Rhinne's test
• Tests air conduction and bone conduction for each ear, separately • Tuning fork; It is placed on the mastoid process until the subject no longer hears a sound - this tests bone conduction. The same fork is then placed near the ear of the subject to determine air conduction • In a normal individual, Air conduction is better than bone conduction due to the amplification mechanisms of the middle ear • Expected with conductive hearing loss - bone conduction is better (last longer) than air conduction • Expected with conductive hearing loss - AC conduction is still better (last longer) than bone conduction |
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Otosklerosis:
• etiology - two structures are involved • Clincal manifestation |
Otosklerosis:
• The bony labyrinth and stapes footplate is gradually replaced by lamellar bone • The stapes fuses with the oval; window --> conductive hearing loss |
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Vestibular Schwannoma
• etiology • Affected structure • Clinical presentation |
Vestibular Schwannoma:
• A benign tumor originating from Schwann cells of the vestibular division of CN VIII • CN VIII is compressed within the internal acoustic meatus • Sensorineural hearing loss and tinnitus |
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Another source of Senorineural hearing loss
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Loss of hair cells in the Organ of Corti (hair cells cannot be replaced)
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The situation where cochlear implants are useful
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When there is sensorineural hearing loss, due to damaged hair cell but the afferent fibers adjacent to the hair cells may still be inact
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