Exam 3: Auditory Flashcards
2 primary qualities of auditory system
Intensity and Frequency
Intensity correlates to….
Loudness
Frequency correlates to….
Pitch
Range of intensity
0-120 dB
Range of frequency
20 to 20k
external ear
pinna and external auditory meatus
middle ear
TM, ossicles
inner ear
cochlea and semicircular canals
Function of middle ear
Overcome impedance mismatch between air and fluid
P=F/A; increase force through lever action and decreasing area of force applied (stapes vs TM)
How much of acoustic impedance is overcome in middle ear?
-30 from mismatch
+28 from middle ear
Types of hearing loss (2)
Conductive and Sensorineural
How to distinguish conductive vs. sensoineural hearing loss
Tuning fork in air and then on bone
3 compartments of cochlea
Scala vestibuli, media, and tympani
Where is the organ of Corti?
On basilar membrane w/in scala media, contains hair cells
Where are higher frequency sounds heard on the basilar membrane?
closer to the base
How does the basilar membrane vary along the cochlea?
thinner, narrower, and more rigid at base
more flexible, wider, and thicker at the apex
How many hair cells per cochlea?
16k
More inner or outer hair cells?
Outer hair cells
Which hair cells convert mechanical vibration into electrical signals?
Inner hair cells
Perilymph vs endolymph
Perilymph: like normal ECF, high Na and Ca
Endolymph: high K
Which lymph fills which compartment?
Endolymph –> Scala media
Perilymph –> Scala tympani and vestibuli
What produces endolymph
stria vascularis
What is the endocochlear potential?
-80mV
Type I vs Type II Auditory Nerve Fibers
Type I innervate IHCs and are myelinated
Type II innervate OHCs and are unmyelinated
Ratios of nerves to hair cells
10: 1 nerve:IHC
1: 10 nerve:OHC
What sound intensity can cause hearing loss?
120 dB
Causes of conductive hearing loss
Otitis media, otosclerosis, malformations of inner ear, perforations of the TM, static pressure, interruptions of ossicle chain, cholesteatoma (skin cyst)
Causes of sensorineural hearing loss
loud sounds, ototoxic drugs, age (presbycusis), genetics
How to differentiate Conductive and Sensorineural hearing loss?
Tuning fork restores hearing in conductive
How many ANFs per cochlea?
30,000
What percentage of ANFs contact IHCs?
95%
Causes of neural hearing loss
8th nerve tumor, auditory neuropathy, multiple sclerosis
What causes sensory hearing loss?
Loss of endotrochelar potential due to vasculitis, metabolic disorders, or immune disorders
