2. Phys of Auditory & vision Flashcards
(41 cards)
what freq has a large deflection a narrow & stiff
high freq
near oval/round window
base of basilar mem
what freq has greatest deflection in the wider and more flexible region
lower freq
near helicotrema
apex of basilar mem
how is freq of sound (pitch) coded
along the basilar membrane there is the greatest deflection.
what does the auditory system do
detects sound and uses acoustic cues to identify and locate sound sources in the environment
what is sound
Oscillations of air pressure that vary rapidly with time.
what is amplitude
sound pressure (intensity) specified by a scale of sound pressure level (SPL) in decibels (dB)
what is freq?
number of oscillations of air pressure per second (Hz).
where does wave propagate from
from base to apex
until point of maximal displacement occurs
how is tonotopy maintained in inner ear
high freq percieved in narrow/stiff (base of basilar mem)
& low freq in wider/flexible (apex of basilar mem
how is the pressure differential produced in cochlea
the cochlea is a closed-structure with one point of entrance and another point of exit for the dissipation of energy, the vibration of the basilar membrane
what does pressure differential cause
shearing force against stationary tectorial mem –> cause stereocilia of outer HC to be displaced
how are inner HCs activated
fluid movement in cochlear duct
how are stereocilia connected & what does movement cause
tip links that transmit force to elastic spring
–> open TRPA1 cells
what is the advantage of mechanotrandsuction
immediate effect -stimulated in 50 us
do not require receptor potential –> increase sensitivity
what is endolymph
the potassium-RICH fluid filling the cochlear duct & the membranous labyrinth;
bathes the apical end HCs.
- Similar to the intracellular fluid (ICF): high in [K+] and low in [Na+].
- Found in scala media
- Produced by the stria vascularis
what is perilymph
the potassium-POOR fluid that bathes the basal end of the cochlear HCs.
- Similar to the extracellular fluid (ECF): high [Na+] and low [K+].
- Found in scala vestibuli and scala tympani
how are NTs released from HC
- stereocilia bathed endolymph –> the opening of the cation channels cause a rapid influx of K+ into the cell –> HC depolarizes.
- –> causes Ca2+ channels at the base of the cells to open. –> NT- filled vesicles fuse with the basilar mem and release NT (glutamate)
- –> afferent cochlear nerve fibers stimulated & transmit this signal to the CNS.
what occurs in upward displacement of basilar mem
Tips of the stereocilia on HCs embedded in the tectorial membrane, and the bodies of HCs rest on the basilar mem.
–> upward displacement basilar mem –> shearing force –> lateral displacement of the stereocilia –> depolarization of the hair cell.
what occurs if there is a downward displacement of basilar mem
A downward displacement –> shearing force–> hyperpolarization of HCS
what are the roles of inner & outer HCs
inner hair cells- hearing. ~ 90% of cochlear nerve fibers
outer hair cells - amplify the signals from inner hair cells.
what is the role of stria vascularis
located in the lateral wall of the cochlear duct (scala media),
produces the endolymph with high levels of K+ (fills membranous labyrinth)
Stratified epithelial cells of SV extend cytoplasmic processes and folds around the capillaries of intraepithelial plexus –> K+ released from capillaries –> across tightly joined cells –> into the endolymph
what are optimal conditions for HC depolarization? How is it maintained
endolymph with high [K+] maintained by stria vascularis
high endocochlear potential (+80 mV) –> drive K+ into HC down [] gradient.
the potential forms what is known as the blood-labyrinth barrier (BLB) = main sites of drug entry to access the inner HC
organization of inner HCs
- = primary source of auditory information
- arranged in a single layer.
- synapse with the peripheral terminal of a primary afferent sensory neuron
- & efferent neuron modulates activity
what do the outer hair cells do? and how to they do this
- =amplify sound waves
- = contractile –> boosts the mechanical vibrations of the basilar membrane
- 3 rows
- synapse with sensory afferent peripheral terminals from spiral ganglia & terminals from efferent ganglia
