L5 + L6 - Audition Flashcards
What is the function of the pinnea?
To amplify sound
What is the auricle?
The ear lone
What did the middle ear evolve from?
the branchial arch skeleton
What did the quadratum and articulare from primitive reptiles develop into?
The malleus and incus
What did the columella from primitive reptiles develop into?
The stapes
Outline Saunder’s compared transfer function experiment
He tested the difference between the 3 ossicle middle ear model belonging to mammals and the 1 ossicle middle ear model belonging to birds. He tested the relative dB that could be detected at certain frequencies. He found that generally mammals can hear much higher frequencies up to 100kHz were as birds could only hear up to 10kHz. Humans are an exception to this as out hearing is limited to a maximum of 10-20kHz.
What is the function of the middle ear?
To enable transfer of airborn sound into the fluid filled inner ear, acting as an impedence transformer.
How does the impedence transformer function of the middle ear work?
The ratio between the tympanic membrane and stapes footplate surface area i very large and the lever action of the malleus to the incus is 1.3:1, this amplifies the pressure to the footplate by another 30dB.
What happens if the stereocilia are pushed towards the kinocilia?
Excitation occurs as the transduction links are stretched
What happens if the kinocilia is pushed towards the steroeocilia?
Inhibition as the transduction links are compressed
What happens when the transduction links are stretched?
The apical ion channels at the tip links re opened letting K into the cell. This opens VGCC which then open both ligand gated and VG potassium channels, extruding potassium into the Scala Tympani. Calcium is also pumped out. Meanwhile NTs are being released which stimulate the auditory afferent nerve fibres, where the sound is converted into an AP travelling to the brain.
What are the 2 types of spiral ganglion cells that afferently innervate the cochlea?
Large myelinated cells which innervate Inner hair cells
Small unmyelinated cells which innervate outer hair cells
What are ribbon synapses in the cochlea specialized for?
High precision temporal sound coding over a wide range of intensities and time periods
What is the main function of the outer hair cells?
They act as a cochlear amplifier
What are otoacoustic emissions?
Sounds emitted from the ear due to the motility of outer hair cells. They can be used to check outer hair cell function.
Outline spontaneous otoacoustic emissions (SOAE)
These occur without a sound stimulus
Present in 20-40% of normal hearing ears
Not used clinically
What are the two types of evoked otoacoustic emissions?
Transitions evoked otoacoustic emissions (TEOAE)
Distortion product otoacoustic emissions
Outline transitions evoked oto acoustic emissions
They are stimulated by a short click
They are fast but have low frequency selectivity
They are absent at hearing loss >30-40 dB
Used to test new-borns hearing
Outline distortion produced oto acoustic emissions
To elicit must use a probe with a mini microphone and two speakers inserted into the ear canal. These then emit two frequencies f1 and f2. these cause overlapping waves on the basilar membrane.In the region of the overlap a distortion with a frequency 2f1-2f2 occurs. This can then be measured by the microphone.
What is the driving force for K influx in the cochlear?
The positive endocochlear potential of 80mV
Where does K recycling take place in the cochlear?
In the supporting cells of the organ of corti, the fibrocytes of the lamina spiralis and the stria vascularis
In the auditory at low frequencies are the action potentials timelocked to the stimulus?
Yes
Is there a smaller frequency detection at high volume?
No there is a larger frequency detection
Is the volume threshold the same for different frequencies?
No it changes
What are the low SR fibres useful for?
Decoding human speech
What are the 3 response components of the cochlea
Cochlear microphones - generated by transduction current through the OHC and follow closely the time course of the stimulus
Summating Potential - a dc potential generated by hair cells
Compound action potential - synchronised response of the auditory nerve fibres to onset of the stimulus
Outline the ascending auditory pathway
Auditory nerve fibres –> Cochlear nucleus –> superior olivary complex –> lateral lemniscus –> inferior colliculus –> medial geniculate nucleus —> auditory cortex
Outline the descending auditory pathway
Inferior colliculus –> cochlear nucleus –> spiral ganglion within bony
What is processed in the acoustic parallel pathways?
Dorsal stream = sound identification
Ventral stream - binaural sound localization
Where do the auditory parallel pathways combine?
The inferior colliculus
What are the two methods of binaural sound localisation?
Interaural level difference
Interaural temporal difference
What is interaural level difference (ILD)?
The difference in volume between the two, due to the acoustic shadow of the head. The minimus difference detectable is 1-2dB
What is the interaural temporal difference (ITD)?
The time between both ears. The minimum difference that can be detected is
Where is ILD processed?
The lateral superior olive (LSO)
How is ILD processed?
Direct excitatory input from the ipsi-lateral spherical cells of the AVCN.
Indirect inhibitory input from the contra-lateral globular cells of the AVCN through the MNTB.
These converge in the LSO.
this is then projected to the inferior colliculus.
Where is ITD processed?
Medial superior olive (MSO)
How is ITD processed?
Direct excitatory input from the ipsi-lateral and contra-lateral spherical bushy cells of th AVCN to the MSO.
Indirect inhibitory input from the ipsi-lateral globular bushy cells of the AVCN via the LNTB
Indirect inhibitory input from the contra-lateral globular bushy cells of the AVCN via the MNTB.
MSO neurons then project to the inferior colliculus
Which hemisphere is speech limited to?
The left
What are on the axes for an audiogram?
On the y axis is he threshold in dBSPL and on the x axis is the frequency
How is air conduction stimulated?
The inner ear is stimulated via a headphone
How is bone conduction stimulated?
Via a bone conduction transducer
What is the presentation for conductive hearing loss on an audiogram?
Normal bone conduction
Air conduction hearing loss
What is the presentation for sensorineural hearing loss on an audiogram?
Air an bone conduction are similarly reduced.
What is the presentation for combined hearing loss on an audiogram
Both have hearing loss however air conduction hearing loss is more severe.
What are the possible causes of conductive hearing loss?
Ear canal blocked
Middle ear infection
Rupture of the ear drum
Pathology of the ossicles e.e. cholesteatome or ostosklerosis
What are the possible causes of sensorineural hearing loss?
Damage and loss of hair cells
Loss of auditory nerve fibres and spiral ganglion cells
Auditory nerve neuropathy/synaptopathy
Pathology of the Stria vascularis
What is an EAS?
A new type of hearing aid which uses acoustical amplification at low frequencies and electrical stimualtion at high frequencies
How does a cochlear implant work?
It stimulates the auditory nerve directly
How do you identify that the gerbil heard a sound?
Use a natural behaviour e.g. jumping on an elevate platform and train it so that when it hears the sound it will jump off
Gerbils to test hearing loss
Tested their ability to notice a gap in the acoustic stimulus at varying volumes. It was found that the older gerbils were worse at this.
