2. Phys of Auditory & vision Flashcards
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
what is otoacoustic emission
- Motility of the outer HC –> basilar membrane & movement could be backward AKA toward the oval window and through the middle ear via the ossicles –> displacement of TM
- result in the ear itself producing a sound ==> this can be measured in the external auditory meatus as otoacoustic emissions (OAE).
1. Originate in the superior olivary complex.
2. Known as olivocochlear efferents
3. Medial olivary complex neurons innervate outer hair cells
4. Lateral olivary complex neurons innervate inner hair cells
what does OAE testing measure
measures absence of sound waves by the cochlear outer HCs in response to sound stimuli
A microphone at the external ear canal detects the low-intensity OAEs (evaluates hearing from middle ear to outer hair cells–>used to screen for sensorineural hearing loss but cannot detect auditory neuropathy)
what do Olivocochlear efferents do
- Reduces electromotility of outer hair cells.
- Decreases basilar membrane motion
- Reduces responses of inner hair cells and auditory nerve fibers
what do Medial ear efferents do
- Attenuates sound.
- Tensor tympani to the malleus and the tympanic membrane
- Stapedius to the stapes (from CN VII).
- Bilateral response to high sound levels.
- Contractions decrease transmission of sound.
- Act at low frequencies.
- May prevent damage, low frequency masking (improving speech discrimination), HC from damage to intense sounds.
- Implicated in tinnitus
what do automatic efferents do
- Arises from 8th cranial nerve
- Sympathetic adrenergic fibers
- Regulates vascular tone in blood supply to cochlea
what is the fxn of dorsal & ventral cochlear nuclei
DCN= integrates the acoustic information with somatosensory information
VCN = Begins processing the temporal and spectral features of the sound.
what do medial & lateral superior olivary complex do
-Receives glutamatergic (excitatory) input
MSO = a map of interaural TIME differences to help localization of sound.
LSO = amap of interaural INTENSITY differences to help localize the source of a sound.
Tonotopic map is maintained
what is the function of inferior colliculus
- suppresses information related to echoes, (that interferes with localization) and arrives at a final estimation of localization of sound along the horizon.
- Information about time and intensity differences converge into the IC to help create a precise origin of sound location along the horizon.
- Tonotopic map is maintained in IC.
what does medial geniculate nucleus do
- Part of the thalamus
Lots of convergence from distinct spectral and temporal pathways, allowing for processing features of speech inflections.
Precise information regarding intensity, frequency, and binaural properties of sound are integrated and relayed onward.
Tonotopic map is maintained.
what is the fxn of primary auditory cortex (A1)
Essential in conscious perception of sound.
Higher order processing of sound (loudness, modulations in volume, rate of frequency modulation).
Tonotopic map is maintained.
what is the secondary auditory association cortex (A2)
Less specifically organized in the tonotopic arrangement than the primary auditory cortex.
This is thought to respond to more complex sounds (music), identifying (naming) a sound, and speech.
Anterior semicircular canal
Rotation in the vertical plane forwards maximally activates the anterior semicircular canal.
horizontal semicircular canal
Rotation in the horizontal plane is best detected by the horizontal semicircular canal
Posterior semicircular canal
Rotation in the vertical plane backwards maximally activates the posterior semicircular canal.
utricle
detects linear acceleration forward and backward.
saccule
linear acceleration up & down
how does cochlear prosthesis work
proble with HC or cochlear N
implant - external & internal component
internal component = receiver - decode signal & deliver electrical signal & electrode array - inserted into cochlea thru oval window & sits in cochlear duct along afferent CN 8 –> electical signal stimulate cochlear N alone basilar men
array - mimic tonotopy
