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49 Cards in this Set

  • Front
  • Back
what are the functions of auditory system?
-determine the frequency, intensity and other properties of sound
-locate the sound
-interprets meaning of sound
where are sensory receptors for auditory system found?
in inner ear(cochlea)
-hair cells, sensory neurons
Def of sound
audible variations in air pressure
-whether air molecules are compressed or rarefied.
frequency
number of compressed or rarefied patches of air that pass by our ear each second

cycles/sec
pitch
intensity
-loudness
-difference in pressure between compressed and rarefied patches of air
what's the cause of conduction deafness and what is it?
-otoschlerosis (ossification of stapes)
-bone conduction >air conduction
What is sensorineural deafness?
-decreased bone and air conduction
3 functions of attenuation reflex?

what is it?
what are the two muscles that contract?
1. to adapt the ear to continuous sound at high intensities(increase the dynamic range we can hear)
2.protects the inner ear from loud sounds
3.suppress low frequencies more. Hight frequency can be heard easily(easier to understand speech)
-delay 50-100msec
-loud sound triggers neural response that causes 2 muscles in middle ear contract to make the chain of ossicles more rigid and the sound conduction to the inner ear diminish.
-Tensor Tympani muscle
-Stapedius muscle
perilymph in which cross sections of cochlea?

properties
scala vestibuli
scale tympani

ionic content similar to CSF
low K+. high Na+
Reissner's membrane

Basilar membrane
Reissner's membrane:separate scala vestibuli from scala media

Basilar membrane:separate scala tympani from scala media
Endolymph

What is endolymph potential?
in scala media
similar to intracellular fluid High K+, Low Na+

-electrical potential 80mV more positive than that of perilymph
-due to ionic concentration differences, by active transport process at stria vascularis
-enhances auditory transduction
What is orgna of corti?
sitting on basilar membrane
-contain auditory receeptor neurons
What is helicotrema?
-at the apex of cochlea, where scala tympani become continuous with scala vestibuli
Stria vascularis
-reabsorbs sodium and secretes potassium against their concentration gradients
-cause of ionic concentration differences between endolymph and perilymph
Steps for inner ear
1.fluid pressure at oval window
2.scala vestibuli
3.helicotrema
4.back down the scala tympani
5.round window (bulge)
Basilar membrane
-flexible, bends in respond to sound
-winder at the apex than at the base by factor of 5
-stiffer 100x at the base than at the apex
Von Bekesy on basilar membrane
-movement of endolymph make basilar memb. bend near its base and start a wave that propagates toward the apex
-high frequency-wave vibrate stiff fibers best, travel short distance
-low frequency-wave vibrate floppy fivers best, travel entire distance
basilar membrane and frequency
-hair cells in these regions of b.m. have receptive fields differing in frequency preference
1. Frequency coding of level of b.m.
2. Mechanical property of b.m.(length of hair cells)
High frequency detected best by Hair cells in _______

Low frequency detected best by Hair cells in _______
base

apex
True/False
Sound wave transform to pressure wave in inner ear
T
organ of cori is composed of?
-hair cells
-supporting structures

where auditory receptor cells which convert mechanical energy into a change in membrane polarization
-all but tectorial memb moves as a unit
Hair cells
-auditory receptor cells
-each one has stereocilia
-in btw basilar memb and reticular lamina which are supported by rods of corti
-form synapses on neurons
Inner hair cells
-btw modiolus and rods of corti
-stereocilia just below the tectorial memb.
Outer hair cells
-farther out than the rods of corti
-stereocilia extend above the reticular lamina into endolymph, tips end in gelatonious substance of tectorial memb.
where are cell bodies of hair cells located?
-in the spiral ganglion within the modiolus
spiral ganglion cells
-bipolar
-neurites extending to the base and sides of hair cells, here they recieve synaptic input
-axons from spiral ganglion enter auditory nerve (a bunch of auditory vestibular nerve)
-projects to the cochlear nucleus in medulla
Transduction of hair cells
-stereocilia in endolymph
-base of hair cell facing perilymph
-K+ driven into the cell in sterecilia

-at rest:mechanical gated channels(linked together)-slightly open, K+ enter the cell
-when b.m. displaced, channels open more
-More K+ enter the cell and depolarizes the cell
-depolarization opens voltage gated Ca2+ channel
-Ca2+ enter the cell
-cause exocytosis of neurotransmitter(glutamate)
-glutamate released and bind with receptor neurons
-A.P in 1st order neuron (spiral ganglion)
Repolarization
-K+ efflux into perilymph through Ca2+ dependent K+ channels and V-gated K+ channels
outer hair cells

motor protein
-cochlear amplifier
-amplify air pressure wave
-motor protein-cause elongation and shortening of har cells. Alter the placement of basilar memb.
-Transduction facilitated when greater displacement of B.M.
T/F
Inner hair cell-95% of info about sound into central auditory system (1 to 1 fidelity)

Outer hair cell inervate more than 1
T
Characteristic frequency
for 1st order neuron (# of spikes generated)
-preference for certain frequency
Tonotopy
-found at all auditory levles
-going from the base to the apex of the cochlea, the b.m. resonates with incresingly lower frequencies. This tonotopy is preserved in the auditory nerve and cochlear nucleus.
-In the cochlear nucleus, there are bands of cells with similar characteristic frequencies; characteristic frequencies increase progressively from posterior to anterior
Isofrequency bands
cortical columns with different tonal receptive fields
Steps of Ventral Cochlear Pathway
-each cochlea is bilaterally represented in the brain

Spiral ganglion(1)
V. cochlear nucleus(2)
(bilaterally)
superior olive(3)
(lateral lemniscus)
Inferior colliculus(4)
MGN(5)
Auditory cortex
how to get deafness in one ear?
-can't get it by lesioning superior olive and on
-lesion V. cochlear nucleus
(receives info from 1 ear L-L R-R)
Intensity coding
3 mechanisms
Soft vs Loud sound

Loud sound
1. stronger displacement than soft(temporal summation)-same hair cells stimulated both cases but greater degree in loud sound.
-more A.P. firing in that 1st order neuron(spiral ganglion neuron)

2.wider area diplaced(spatial summation)
more hair cells responding
more 1st order neurons responding

3.special hair cells-high threshold
activated if the basilar memb.stimuated beyond threshold

Intensity coding at b.m. interferes with frequency coding
3 problems with Tonotopy
1. basilar memb. is also dependent on intensity
2. tonotopy maps do not represent sound frequencies below 200Hz, but we can hear down to 20Hz.
3. Neurons can not faithfully represent sounds beyond 500Hz because AP lasts 1-2msec
500events/sec=500Hz
Phase Locking
-the consistent firing of a cell at the same phase of a soundwave
-frequency encoded in timing of neuronal firing

-respond to low frequencies (20-200Hz)1. response on every cycle of the stimulus
2. response on some fraction of the cycles
Volley principle
-at intermediate frequencies(500Hz-4KHz) group of neurons that are sensitive to same frequencies have to work together so that every cycle can be represented. (pooled activity)
-group of neurons, each responding to different cycles of the input signal. It is possible to have a response to every cycle
T/F
Low f (20-200Hz)-phase lock
Intermediate f (500Hz-4KHz)-phase locking, volley, tonotopy

High f(above 4KHz)-tonotopy
-no phase locking can occur due to intrinsic variability in timing of A.P.
T
Sound localization
-duplex theory

horizontal localization (2 ears)

vertical
Horizontal localization
2 methods
1. Interaural time delay
2. interaural intensity difference
Interaural time delay
-use the distance of both ears
-sudden sounds of all frequencies and continous sounds of 20-2000Hz
-the time at which sound arrives at both ears is different because ditance btw ears is 20cm
-if sound source directly infront of face, interaural time=0

continuous-use interaural time delay of phase of sound wave (only for low and intermediate frequencies)
Sudden sound-no problem
Interaural intensity difference
-for continuous sonds with high frequencies (2-20KHz)
-If sound comes from the right, the left ear will hear a significantly lower intensity
-higher f sound will be detected with louder intensity
-head casts a sound shadow to ear furthest from sound
-lower intensity sound at one ear is a cue that the sound came from the other direction.
-No sound shadow at low frequencies
-if sound source directly infront of face, 0
binaural neurons
-neurons that recieve info from more than 1 ear
-
T/F
Neurons in the cochlear nuclei are monaural neurons since they only receive afferents from one ear. Later ones are binaural neurons
T
Superior olivary neurons
Binaural receptive fields
different populations of neurons respond best to specific interaural time delays
A1 primary auditory cortex
EE
El
EE-summation columns(neurons respond best to sound info from both ears)

El-suppression columns (neurons respond best to sound info from one ear)
Sound localization in Vertical plane
-sound reflected by Pinna