Auditory System Flashcards
What is the function of the outer ear
Collection of sound; protection, funneling of sound, and spectral filtering for sound localization
What is the function of the inner ear
Transduction of sound; functions as the sensory transducer of sound-driven vibrations, gravity, and acceleration into neuronal signals via inner hair cells
What is the function of the middle ear
Conduction/Amplification of sound; serves as an impedance matching device, allowing for adequate transfer of energy from air-borne sound to fluid-filled cochlea
What is the route of conduction of sound from the middle to the inner ear?
Tympanum –> malleus –> incus –> stapes –> oval window –> scala vestibuli –> helicotrema –> scala tympani –> round window
What is the stapedius reflex?
Contraction of the stapedius in response to high intensity sounds or just before speaking
What is the route of the stapedius reflex?
Loud sound travels to auditory nerve –> V. Cochlear nucleus –> S. Olivary nucleus –> facial motor nucleus, which release ACh to cause stapedius muscle contraction
How does sound transduction occur?
Pressure oscillations in the cochlea induce movement (vibration of the organ of corti); different parts of the basilar membrane move optimally at different frequencies of sound
What is endolymph
Contains high K+ and low Na+ and protein. +80mV, secreted from stria vascularis via Na/K
What is perilymph
Similar to interstitial fluid, with high Na+ and Cl-, low protein
What is the difference between perilymph and endolymph
Perilymph has high Na+, endolymph has low Na+; both have low protein; perilymph fills the vestibuli and tympani while endolymph fills the cochlear duct (media)
What is the result of the Rinne test if there is unilateral conduction hearing loss?
Bone louder than airborne
What is the result of the Weber test if there is unilateral conduction hearing loss?
Louder on affected side
Where does sound travel faster, water or air?
WATER, but most of it gets rejected
Which bone of the middle ear is referred to as the “anvil”
incus
Which bone of the middle ear is referred to as the “stirrup”
stapes
Which bone of the middle ear is referred to as the “hammer”
Malleus
What is the innervation of the middle ear?
A branch of the facial nerve and a branch of the trigeminal nerve
What is the musculature of the middle ear
Stapedius muscle and tensor tympani muscle
What do the facial nerve branch and stapedius muscle act on?
The stapes; nerve innervates the stapedius muscle
What do the trigeminal nerve branch and tensor tympani muscle act on?
tympanic membrane (muscle travels through the proximal portion of the eustachian tube); nerve innervates the tensor tympani
How does contraction of the middle ear muscles (stapedius and tensor tympani) affect amplification
Decreases amplification of the movements of the middle ear ossicles (increased impedance)
What is the purpose of contraction of the middle ear muscles
Protection against loud sounds, especially at lower frequencies to allow detection of higher frequencies
Where does the perilymph drain?
From the perilymph duct into the CSF of the subarachnoid space
What is the helicotrema
Apex of the cochlear labyrinth. The hair cells near this area best detect low frequency sounds.
What are the 3 fluid filled chambers of the cochlea?
Scala vestibuli, scala tympani, and scala media (cochlear duct)
What is the organ of corti
Site of mechano-electrical transduction
What is the frequency discrimination in humans?
0.2%
What three factors does frequency discrimination depend upon?
- tonotopic organization of hair cells
- membrane potential
- cilia length
What is place theory?
The PLACE along the basilar membrane where the optimal hair cell discharge is attained; explains how frequencies of sound are coded
What causes the bending of cilia?
Basilar membrane moving up and down, resulting in the organ of corti sliding in and out relative to the tectorial membrane
Does the basilar membrane go up or down during excitation? inhibition?
Excitation - up
inhibition - down
How does inner hair cell transduction work?
K+ and Ca++ influx results in glutamate release, which acts on AMPA-type glutamate receptors of cochlear nerve fibers
What is the auditory pathway, starting from the dorsal acoustic stria
Cochlear nuclei –> dorsal acoustic stria –> contralateral to the nucleus of lateral lemniscus (pons) –> inferior colliculus (midbrain) –> medial geniculate nucleus (midbrain) –> primary auditory cortex (AKA temporal gyrus, Heschl’s gyrus, area 41)
What is the auditory pathway, starting from the trapezoid body
Cochlear nuclei –> trapezoid body –> bilateral superior olivary nuclei (pons) –> bilateral nuclei of lateral lemniscus –> bilateral inferior colliculus –> unilaterally to medial geniculate nucleus –> primary auditory cortex
What is the auditory pathway, starting from the intermediate acoustic stria
Cochlear nuclei –> intermediate acoustic stria –> nucleus of the lateral lemniscus –> inferior colliculus –> medial geniculate nucleus –> primary auditory cortex
What are the 5 main classifications of deafness?
Conduction, sensorineural, neural, central, genetic
What is the sound intensity level equation?
L = 20log(P/Pref)
What is the decibel loss equation?
-20log(Ppt/Pnl)
A noise level of 20 decibels would best equate to which of the following? A) a quiet room at night B) A busy street C) a pneumatic drill D) Aircraft taking off
A) Quiet room
A noise level of 60 decibels would best equate to which of the following?
A) Personal music player at high volume
B) A busy street
C) An ordinary spoken conversation
D) Aircraft taking off
C) an ordinary spoken conversation
A noise level of 70 decibels would best equate to which of the following? A) a quiet room at night B) A busy street C) a pneumatic drill D) Aircraft taking off
B) a busy street
A noise level of 100 decibels would best equate to which of the following? A) a quiet room at night B) A busy street C) a pneumatic drill D) Aircraft taking off
C) a pneumatic drill
A noise level of 105 decibels would best equate to which of the following? A) Personal music player at high volume B) A busy street C) An ordinary spoken conversation D) Aircraft taking off
A) Personal music player at high volume
A noise level of 110 decibels would best equate to which of the following? A) Personal music player at high volume B) A busy street C) An ordinary spoken conversation D) Aircraft taking off
D) Aircraft taking off
What is BAER used for?
Brain stem auditory evoked response is used to assess auditory function in infants and in general in patients not able to respond
What are the steps in audiometry?
- present different tones to each ear
- increase intensity to threshold
- Hearing ability at given frequency is given as threshold pressure compared to normal population and is presented as hearing loss in decibels
What is the amount of decibel loss that is considered abnormal?
> -20 dB loss
What would be the decibel loss if a patient’s threshold pressure is 1000x normal?
60
What is conduction deafness?
Decreased vibrations to the basilar membrane and decreased air conduction; bone conduction is okay
Which frequency range is affected in conduction deafness?
Broad range, but especially low frequencies
Which frequency range is affected in conduction deafness?
Broad range, but especially low frequencies
What are possible causes of conduction deafness?
Foreign objects/wax in the ear canal, otitis media, otosclerosis
What is otosclerosis?
A cause of conduction deafness; overgrowth of temporal bone around oval window, limiting stapes movement
What are the treatments for conduction deafness?
Remove cause, surgery, hearing aids
What are the presynaptic changes during temporary conduction hearing loss?
Decrease in VGlut1 in auditory nerve endings and SV size
What are the postsynaptic changes during temporary conduction hearing loss
Thicker PSD, increased GluA3 AMPARs - decrease in vesicular glutamate transporter postsynaptic densities altered as well
What are presynaptic changes when hearing is restored after temporary conduction hearing loss
Increased SV size and density in auditory nerve endings
What are the postsynaptic changes when hearing is restored after temporary conduction hearing loss
Thicker and larger PSD, increased GluA3, fewer GluA2 AMPARs
What is sensorineural deafness
Loss of both air and bone conduction
What frequencies are affected in sensorineural deafness
High frequencies
What are some causes of sensorineural deafness?
Chronic loud sounds, aminoglycoside antibiotics (parental use of streptomycin, neomycin, gentamicin, esp. long duration use), quinine, prolonged high doses of aspirin, vaccines (rubella), old age (presbyacusis)
What is the treatment for sensorineural deafness?
Hearing aids (microphone-amplifier-speaker)
Hair cell loss can be associated with which classification of deafness?
Sensorineural
What is the purpose of cochlear implants?
They are important for severe and complete hearing loss; they are multi-channel stimulatory devices placed in the cochlear duct
What is neural deafness?
Unilateral, sensorineural deafness
What are the most common causes of neural deafness?
Schwannoma or acoustic neuroma of auditory nerve in the internal auditory canal
What is central deafness
Deafness that may manifest as auditory hallucinations (schizophrenia, temporal lobe damage, seizures), pure word deafness, auditory agnosia, and amusia (right hemisphere)
What are possible causes of central deafness?
Lesion in the CNS causing abnormal processing of auditory signals (very rare) OR bilateral brainstem injury (inferior colliculus) OR cortical deafness (bilateral embolic stroke Heschl’s gyri)
What is the prevalence of genetic deafness?
1/1,000
Which genes are affected in genetic deafness?
Connexins 26 and 30, SLC26A4, and mitochondrial genes
