Auditory System

Front 1

what are the functions of auditory system?

Back 1

-determine the frequency, intensity and other properties of sound
-locate the sound
-interprets meaning of sound

Front 2

where are sensory receptors for auditory system found?

Back 2

in inner ear(cochlea)
-hair cells, sensory neurons

Front 3

Def of sound

Back 3

audible variations in air pressure
-whether air molecules are compressed or rarefied.

Front 4

frequency

Back 4

number of compressed or rarefied patches of air that pass by our ear each second

cycles/sec
pitch

Front 5

intensity

Back 5

-loudness
-difference in pressure between compressed and rarefied patches of air

Front 6

what's the cause of conduction deafness and what is it?

Back 6

-otoschlerosis (ossification of stapes)
-bone conduction >air conduction

Front 7

What is sensorineural deafness?

Back 7

-decreased bone and air conduction

Front 8

3 functions of attenuation reflex?

what is it?
what are the two muscles that contract?

Back 8

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

Front 9

perilymph in which cross sections of cochlea?

properties

Back 9

scala vestibuli
scale tympani

ionic content similar to CSF
low K+. high Na+

Front 10

Reissner's membrane

Basilar membrane

Back 10

Reissner's membrane:separate scala vestibuli from scala media

Basilar membrane:separate scala tympani from scala media

Front 11

Endolymph

What is endolymph potential?

Back 11

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

Front 12

What is orgna of corti?

Back 12

sitting on basilar membrane
-contain auditory receeptor neurons

Front 13

What is helicotrema?

Back 13

-at the apex of cochlea, where scala tympani become continuous with scala vestibuli

Front 14

Stria vascularis

Back 14

-reabsorbs sodium and secretes potassium against their concentration gradients
-cause of ionic concentration differences between endolymph and perilymph

Front 15

Steps for inner ear

Back 15

1.fluid pressure at oval window
2.scala vestibuli
3.helicotrema
4.back down the scala tympani
5.round window (bulge)

Front 16

Basilar membrane

Back 16

-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

Front 17

Von Bekesy on basilar membrane

Back 17

-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

Front 18

basilar membrane and frequency

Back 18

-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)

Front 19

High frequency detected best by Hair cells in _______

Low frequency detected best by Hair cells in _______

Back 19

base

apex

Front 20

True/False
Sound wave transform to pressure wave in inner ear

Back 20

T

Front 21

organ of cori is composed of?

Back 21

-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

Front 22

Hair cells

Back 22

-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

Front 23

Inner hair cells

Back 23

-btw modiolus and rods of corti
-stereocilia just below the tectorial memb.

Front 24

Outer hair cells

Back 24

-farther out than the rods of corti
-stereocilia extend above the reticular lamina into endolymph, tips end in gelatonious substance of tectorial memb.

Front 25

where are cell bodies of hair cells located?

Back 25

-in the spiral ganglion within the modiolus

Front 26

spiral ganglion cells

Back 26

-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

Front 27

Transduction of hair cells

Back 27

-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)

Front 28

Repolarization

Back 28

-K+ efflux into perilymph through Ca2+ dependent K+ channels and V-gated K+ channels

Front 29

outer hair cells

motor protein

Back 29

-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.

Front 30

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

Back 30

T

Front 31

Characteristic frequency

Back 31

for 1st order neuron (# of spikes generated)
-preference for certain frequency

Front 32

Tonotopy

Back 32

-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

Front 33

Isofrequency bands

Back 33

cortical columns with different tonal receptive fields

Front 34

Steps of Ventral Cochlear Pathway

Back 34

-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

Front 35

how to get deafness in one ear?

Back 35

-can't get it by lesioning superior olive and on
-lesion V. cochlear nucleus
(receives info from 1 ear L-L R-R)

Front 36

Intensity coding
3 mechanisms

Back 36

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

Front 37

3 problems with Tonotopy

Back 37

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

Front 38

Phase Locking

Back 38

-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

Front 39

Volley principle

Back 39

-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

Front 40

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.

Back 40

T

Front 41

Sound localization

Back 41

-duplex theory

horizontal localization (2 ears)

vertical

Front 42

Horizontal localization
2 methods

Back 42

1. Interaural time delay
2. interaural intensity difference

Front 43

Interaural time delay

Back 43

-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

Front 44

Interaural intensity difference

Back 44

-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

Front 45

binaural neurons

Back 45

-neurons that recieve info from more than 1 ear
-

Front 46

T/F
Neurons in the cochlear nuclei are monaural neurons since they only receive afferents from one ear. Later ones are binaural neurons

Back 46

T

Front 47

Superior olivary neurons
Binaural receptive fields

Back 47

different populations of neurons respond best to specific interaural time delays

Front 48

A1 primary auditory cortex
EE
El

Back 48

EE-summation columns(neurons respond best to sound info from both ears)

El-suppression columns (neurons respond best to sound info from one ear)

Front 49

Sound localization in Vertical plane

Back 49

-sound reflected by Pinna