reminder: basilar membrane & frequencies
stiff peak- high frequency
floppy apex: low frequency
analysis of complex sound waves
breaks down complex waves and represents in different places along membrane
afferant and efferants to the organ of corti
95% afferant on inner hair cell (do most of the hearing)
- 20 afferants converge onto each IHC
90% efferant on outer hair cells
tuning curves in tired animals
saw that tuning curves were best when animal was fresh, when animal got tired curve became broader and lost peak (similar to basilar membrane)
- something was weakening and losing ability
outer hair cells
motile and involved in cochlear amplification
- gain control and frequency tuning in cochlea through efferant innervations (oliviocochlear bundle)
what is the molecular motor
most likely prestin
- binds chloride when cell is hyperpolarized there is a negative charge and Cl is repelled into expanded state of molecule
cochlear feedback loop
chloride goes out: hair cell shortens
positive loop: shortening of hair cells causes basilar membrane to move, sound causes motion which is amplified, depolarizes, shortens and causes more motion
what are the tuning curves in animals with no OHC or without prestin
without prestin gene- similar to the dead animals
otoacoustic emissions
generated by OHC
structure of a force conveying cadherin bondessential for inner ear mechanotransduction
made up of 2 types of cadherin molecules
- extracellular loops lock into eachother
- have Ca binding sites
- when you change extracellular Ca hair cell stops responding to sound because tip link gets disrupted
mechanoelectrical transduction mediated by hair cells
spring loaded tip links gate channels physically
- pushes to the right which causes depolarization and potassium rushes in
- high K concentration allows K to flow in (scala media)
directional response of transduction
rectification allows flow in one direction but not the other
- large depolarization response
- not much hyperpolarization response (not equal)
graded mechanoelectrical transduction currents
- adapt to constant stimulation
responds to positive deflection but not to negative - different decays because adaptation (channels r closing)
- look at slides
slow adaptation
when tiplink is stretched it opens channel and slides down
- reducing tension and closing channels
- mediated by myosin motors
- moves back to starting position to re-establish tension
what does adaptation of hair cells do
- shifts the operating range of the channel
- in noisy environment you can still be able to hear sounds
- curve shifts to the right
what myosin is implicated in adaptation
myosin 1c
