lecture 18 (test 2) Flashcards
how many auditory nerves innervate each hair cell
5-30
transmission occurs though the cochlear brach via the
vestibulocochlear nerve
where do cell bodies of afferent fibers lie
in the cochlear ganglion
afferent axons synapse within the
brainstem
hair cells are innervated with afferent fibers in what fashion
systematic and topographic fashion
characteristic frequency
lowest point on tuning curve
frequency at which afferent fiber is most sensitive
how do we obtain a tuning curve
absolute threshold experiment
take electrode and place in auditory nerve near a nerve fiber
fibers that innervate near the base of the basilar membrane respond most strongly to
high frequencies
what are the 2 ways we encode sound frequency
1) looking at response of individual auditory nerve fibers
2) looking at pressure changes of sound wave
what is it called to look at the pressure changes in a sound wave
phase locked response
true phase locking can only occur up to
400-500 Hz
volley principle
neurons work together to create a high frequency response
dispersed phase locking up to 4000Hz
can neurons actually fire at 10 000Hz
nope
temporal code
states the firing rate of an auditory nerve attached to a hair cell will match the incoming sound frequency
how long is a average AP
2ms
low spontaneous fibers
- low action potential frequency
- high activation threshold
- activates at high intensities
- saturates higher intensities
- does not fire till sound is loud
high spontaneous fibers
- high action potential frequency
- low activation threshold
- activates at low intensities
- very sensitive
- plateau at about 30 dB
auditory system determines frequency of incoming sound by looking at
pattern of firing across ALL afferent nerve fibers
contralateral
opposite side
ipsilateral
same side
where does spinal ganglion synapse onto
CNS in the medulla
what are cochlear nuclei sensitive to
each only sensitive to sound from one ear
where does the calculation occur that determines when sound reaches each ear
superior olive
response modification
auditory signals are processed to some degree in some structures, excitement and inhibition occurs at each relay site
tonotopic organization
place code
laterality
extent to which subcortical structures can be separately driven by the 2 ears
most neurons above what are binaural
cochlear nucleus
contralateral inputs are usually
excitatory
ipsilateral inputs are usually
excitatory or inhibitory
as we get closer to auditory cortex there is
more integration from both sides
where is the primary auditory cortex located
superior temporal gyrus in the temporal lobe
where is the secondary auditory cortex (V2) located
directly surrounding the primary auditory cortex
what does area V2 process
more complex signals
conductive hearing loss
when outer or middle ear are affected, leading to reduced transmission of sound to the cochlea
congenital hearing loss
hearing loss in children before language development causes deaf-mutism the absence of language vocalization ability
can be genetic or caused by an issue in the birth process
acquired hearing loss
occurs later in life
Otitis media
middle ear infection
inflation of the eustachian tube
changes ear drum transmission
fluid build-up interferes with ossicle vibration
prevalent in children (tube smaller and more horizontal)
Otosclerosis
inherited bone disease, producing abnormal development and function of the ossicles
increased accumulation of calcium on ossicles
surgeons can shave off to allow vibration again
advances in microsurgery allow ossicle repair or replacement
sensorineural hearing loss
more common and most frequent damage to hair cells or auditory nerve causes may include: ingestion of toxins traumatic injury tumor disease noise-induced hearing loss (NHL)
do our hair cells regenerate
nope
types of hereditary hearing loss
Usher syndrome
Waardenburg syndrome
presbycusis
hearing loss that occurs gradually by effects of aging
loss begins with high-frequency sounds
otolaryngologists (ENT)
clinical diagnosis of auditory disorders
audiologists
evaluate hearing function
tests audiologists use
Rinne test
conductive hearing loss rinne results
louder when tuning for on bone than in air
hearing aids work better when
work better when no hair or cochlear function is impaired
components of hearing aid
small microphone
electronic amplifier
small speaker
the main problem with hearing aids
don’t want to amplify all noises