Lecture 21: Hearing Flashcards
Thursday 13th March 2025
What scale is the magnitude of sound expressed on?
A logarithmic scale
What is the equation for dB SPL?
dB SPL = 20 x log10(P/Pref)
dB SPL, decibels sound pressure level
Where P is the sound pressure and Pref for the threshold of human hearing at 4kHz
What is the loudest tolerable sound?
Loudest tolerable sound is 120dB SPL (106 fold over threshold)
What is the basilar membrane?
The mechanical analyser of sound
Is it true that the 3 compartments of the cochlear are filled with fluid?
Yes
Does the basilar membrane vary along its length?
Yes, the membrane is thin and floppy at the apex, and thicker and taught at the base
Is the cochlea covered by hair cells?
Yes
The sensitivity of the cochlea is too great and the frequency selectivity too sharp to result solely from the passive mechanical properties of the cochlea
There must be a means of amplifying sound, especially at low sound intensities
The sensitivity of the cochlea is too great and the frequency selectivity too sharp to result solely from the passive mechanical properties of the cochlea
There must be a means of amplifying sound, especially at low sound intensities
What are Otoacoustical emissions?
Sounds produced by the ear
What is prestin?
The motor protein in the plasma membrane
What do the movements of cilia generate in hair cells?
Potentials
What is the Stereocilia?
The site if mechanotransduction
The endocochlear potential provides the driving force on K+ to give the inward currents into hair cells during mechano-sensory transduction
The endocochlear potential is essentially a K+ diffusion potential that is generated across the KCNJ10 K+ channel by the very low K+ concentration in the intrastrial fluid spaces and the high K+ concentration in the cytosol of intermediate cells.
The endocochlear potential provides the driving force on K+ to give the inward currents into hair cells during mechano-sensory transduction
The endocochlear potential is essentially a K+ diffusion potential that is generated across the KCNJ10 K+ channel by the very low K+ concentration in the intrastrial fluid spaces and the high K+ concentration in the cytosol of intermediate cells.
What are the advantages of K+?
Influx of K+ ions into the sensory cells causes the least change in the cytosolic concentration compared to any other ion. This is because K+ is by far the most abundant ion in the cytosol.
Influx and extrusion of K+ are energetically inexpensive for the sensory cell since both occur down an electrochemical gradient.
Remember the hair cells still have a negative resting membrane potential because their basolateral membrane is not in the high K+ endolymph.
Efflux of K+ through the basolateral membrane generates a resting membrane potential in the normal way
Remember the hair cells still have a negative resting membrane potential because their basolateral membrane is not in the high K+ endolymph.
Efflux of K+ through the basolateral membrane generates a resting membrane potential in the normal way
- There is a 140mV of driving force driving potassium into the cell.
- There is a 65mV driving force driving K+ out of the cell
- There is a 140mV of driving force driving potassium into the cell.
- There is a 65mV driving force driving K+ out of the cell
How many genes have been identified for hearing loss?
More than 14
Where do the genes for hearing loss come from?
- Some genes are expressed in hair cell
- Some genes are expressed in supporting cells/ striavascularis
Is it true that deafness mutations affect potassium recycling in the cochlea?
Yes
Is it true that mutations that affect the movement of potassium cause hearing loss?
Yes
- Develoment of the cochlea can be affected if C26 is deleted early, and not deleted late.
- However, hearing deficits can take time to appear
- There is a 140mV of driving force driving potassium into the cell.
- There is a 65mV driving force driving K+ out of the cell
What can the C26 mutation cause?
Hair cell degeneration (hair cells themselves do not express connexins). This degeneration can take time to occur.
Affects the electromotility of the outer hair cells (OHCs do not express connexins)
The OHCs still show electromotility but the active cochlear amplification is reduced
Hair cells are not only found in the cochlear, they are also found….
In the vestibular system
What are spiral ganglion neurones?
Spiral ganglion neurons are the afferent neurons contacting hair cells
They also encode the intensity of spound
They only innervate one hair cell, but one hair cell can be innervated by 10 spinal ganglion neurones
