1
Q
what is the function of oval window?
A
entry point for sound
footplate of stapes pushes fluid inside the cochlea
2
Q
what is the function of scala vestibuli?
A
upper chamber
filled with perilymph
first to receive fluid VIBRATION from stapes through oval window
3
Q
what is the function of scala tympani?
A
lower chamber
also perilymph
4
Q
what is helicotreme?
A
apex connection between the scala vestibuli and scala tympani allowing fluid to move into both chambers( vestibuli and tympani )
5
Q
what is the function of cochlear duct/ scala media ?
A
middle chamber
contains endolymph
the organ of corti
tectorial membrane
6
Q
function of basilar membrane ?
A
has/supports organ of corti
vibrates up and down in response to sound ( UP AND DOOWNW )
7
Q
Function of tectorial membrane?
A
stiff membrane that stereocilia push against to create shearing or HORIZONTALL MOVEMENT
as the basilar membrane moves up and down it pushes the hair cells stereocilia against the overlying tectorial membrane
so the tectorial membrane moves with organ of corti creating a wiper like motion that bends the hair cells
8
Q
Function of round window?
A
Pressure release outlet
prevents fluid lock up
the entire perilymph moves instantly once the stapes pushes the oval window —> NO DELAY
this creates waves that travel all the way to the round window to dissipate
9
Q
basilar membrane vs frequencies?
A
specific parts in the basilar membrane respond to specific frequencies
so depending on the sound frequency specific areas in the basilar membrane which correspond to that specific frequency will best vibrate
10
Q
high frequency?
A
cause maximal vibration at the base near the oval window —> NARROW STIFF
11
Q
Mid frequency?
A
vibrates in the middle turns /parts of the cochlea
12
Q
low frequency?
A
vibrates the apexx–> Wide , flexible, near the HELICOTREMA
13
Q
What is tonotopic organization ?
A
specific physical locations respond to specific frequencies
14
Q
importance of tonotopic organization ?
A
the same tonotopic pattern is the same all way the to the cortex
meaning certain cortical regions respond to certain sound frequencies
15
Q
where are low frequencies processed ?
A
antero lateral auditory cortex
16
Q
where is high frequency processed ?
A
postero medial auditory cortex
17
Q
a sound of 8k Hz note will stimulate which part of the cochlea ?
A
the base –> near oval window
cuz 8k is very high frequency
18
Q
a sound of 250 hz will stimulate?
A
the apex of the cochlea near the helicotrema
Cuz its low frequency
19
Q
what is the actual sensory organ for hearing?
A
organ of corti
20
Q
describe the organ of corti?
A
sits on top of the basilar membrane inside scala media
it converts mechanical vibration into electrical signals
tectorial membrane is hanging over the organ of corti, stereocillia of outer hair cells are embedded in it ( tectorial membrane )
it creates shearing force of to bend the sctereocilia
when the basilr membrane goes up/down the tectorial membrane shifts horizontelly, this produces horizontal shearing motion
21
Q
what happens when sound vibration hit the stapes?
A
it will make the footplate of the stapes set up a series of TRAVELLING WAVESS in the perilymph of scala vestibule
22
Q
what happens to its height of waves in the perilymph ?
A
increases to the maximum and then drops off rapidly
23
Q
is the distance always the same?
A
no
The distance from the stapes to this point of maximum height varies with the frequency of the vibrations initiating the wave
24
Q
summarize what happens when the stapes push the oval window?
A
1- traveling wave is created in perilymph of scala vestibuli
2- Wave reaches a point of basilar membrane that resonates most at that sound frequency as we discussed ( specific regions in the basilar membrane best respond to specific frequencies )
3- the amplitude rises to a peak in that point then drops sharply
4- each frequency therefore has a unique place of maximal basement membrane displacements
25
note about basilar membrane and vestibuli?
basilar membrane and scala vestibuli are not directly in contact with each others
the perilymph of scala vestibuli is continuous with the scala tympani
so the waves in the scala vestibuli can still create a pressure difference across the scala media
plus the pressure in reissner membrane can transfer to the basilar membrane as well
26
the stereocillia of the hair receptors are rigid?
yes they are tightly fixed in a rigid structure
27
where are the stereocilia fixed in?
reticular lamina
triangular rods of the corti
Basilar fiber
these structures hold the stereocilia in place and prevent them from collapsing or bending randomly and only bend when an actual shearing force occurs
28
how does basilar membrane respond to sound waves?
Vibrates and move up and down
vibration in the cochlea naturally move the basilar membrane up and down --> vertical
29
what is the movement of reticular lamina in response to the movement of basilar membrane up and down?
Inward and outward
30
when does excitation happen?
when the hair cells bend toward the longer ones
31
hair cells only respond to which type of movement?
horizontal
they are built to detect side to side movement NOT VERTICAL MOTION
32
how does vertical movement of the basilar membrane become horizontal so hair cells can detect it?
Tectorial membrane
33
how so?
tectorial membrane is anchored differently from the basilar membrane
so when BM goes up and down the tectorial membrane lags or moves horizontally creating relative movement
34
what causes the stereocilia to bend away or toward?
the difference in motion between the tectorial membrane and basilar membrane:
if move toward = depolarization n excitation
if move away = hyperpolarize
35
note about tectorial membrane and reticular lamina ?
they were considered one structure but now its two separate
stereocilia are embedded in the tectorial membrane and the movement of the tectorial membrane leads to depolarization
so if it wasnt horizontal vibration, the hair cells would not bend easily to any direction and sound would probably note be heard at all because theres no tipping of stereocilia --->no ap = no sound perceived
36
so in summary what is the movement of basilar membrane and whats is the movement of stereocilia ?
basilar = up and down
stereocilia = left or right
37
what do waves do inside the basilar membrane?
they initiate a response when they reach the region of the basilar membrane that matches their respective sound frequency
38
what happens to the basilar membrane if the stimulation is further away from the oval window ?
it becomes wider and more flexible
39
why is this flexibility?
better for detecting low frequency waves
remember we said low frequency voices go to the helicotrema which is the apex and further away from the oval window
40
what happens to the basilar membrane if the stimulation near the oval window ?
stiff and narrow
so if you are close to window = stiff and narrow
and if you go far to the helictorema = wide and flexible
41
what part of the basilar membrane is stimulated by high frequency?
near the oval window
stiff and narrow
42
what part is stimulated by low frequency?
helicotrema
flexible and wide
43
explain the function of round widnow?
when the stapes pushes the oval window to move fluid inside the cochlea ---> allowing sound to be detected by hair cells
As stapes pushes in = round window pushes out to relieve pressure enabling the fluid to move properly
44
what would happen if round window was missing or stiff?
the stapes would be pushing against an immovable fluid and there would almost no movement inside the cohclea
this lack of movement would cause significant hearing loss about 60 dB
45
What about intesnity ?
we have 2 theories for it:
Firing rate hypothesis
Number of neurons hypothesis
both are by prof david heeger
46
what is firing rate hypothesis ?
Louder sound = greater cell deflection = higher action potential rate
47
what is number of neurons hypothesis ?
Louder sound = wider region of BM virbates = more neurons activated
48
so how is frequency represented by the basilar membrane?
frequency = which location on the BM is stimulated
49
what about loudness according tot he theory?
intensity = loudness
its how much neural activity ( rate or number of neurons ) is produced
50
core idea of firing rate hypothesis
?
louder sound cause greater basilar membrane displacement = greater depolarization = higher firing rate in auditory nerve
as the hair cells are bent more strongly the receptor potential becomes larger which increases the frequency of action potentials in the cochlear nerves
51
what encodes intensity ?
frequency of action potentials
because more bending = more open channels = stronger depolarization = more neurotransmitter release
weaker sound = small stereocilia bend --> few Aps per second
Loud sound = stronger bend = many AP per second
52
so what how does brain interpet the loudness of the sound ?
by the rate of AP
more ap per second = loud
few ap per second = weak
53
what is the core idea of number of neuron hypothesis ?
louder sounds activate wider area of basilar membrane
leading to recruiting MORE hair cells = STIMULATE MORE NERVE FIBERS
larger amplitude waves cause the area of basilar membrane excitation to Spread - activating adjacent hair cells that would normally be silent at low intesnity
54
in the number of neuron hypothesis how does the brain interpret the loudness?
higher number of active neurons = loud
low number of active neurons = quiet
a quiet sound activates only a small core group of neurons at one point on BM
sound gets louder = vibration spread laterally = more hair cells fire = more fibers send signals
55
what are two types of specialized hair cells we have in the cochela?
hair cells = nerve cells
Internal
External
56
describe inner hair cells ?
ONE ROW
about 3500 cells , 12 qm in diameter in each cochlea
less in number but larger in size
57
describe external ouer hair cells?
3 to 4 rows
20k
8qm in diameter
more in number but smaller size
58
what is the type of hair cell that is the main sensory receptor ?
inner one
59
why inner one?
90-95% of auditory nerve fibers synapse in the inner hair cells
60
what happens if the inner hair cells are destroyed ?
complete deafness
61
what is the function of outer hair cells then if inner is sesnory?
amplify and fine tune vibration
improve clarity and sensitivity
62
what happens if you lose outer hair cells?
you would still hear
but poorly -muffled unclear
if outer hair cells are excluded you would still be able to hear but sound would seem duller or quieter or unclear because fine tuning and amplification would be lost
63
direction of bending matter?
yes
Toward the longest stereocilia = depolarization / excitatory
Away = hyperpolarization
64
which channels are opened when bending happens ?
mechanically gated potassium channels K
endolymph is very K rich
65
the tip of hair cells is embedded in?
thin membrane = tectorial membrane
66
which hair cell type is majorly innervated by cochlea nerve?
Inner hair cell
90-95% of the cochlear nerve
important for sound detected
67
% of cochlear nerve innervating outer hair cell?
5-10%
but damage to it only affect the quality of hearing but doesnt eliminate it
68
what is tunning phenomenon ?
Outer hair cells involved in controlling the sensitivity of inner hair cells to different sound pithces
inner hair cells are essential for hearing itself cuz they convert sound vibration into signalss that reach the brain
losing inner hair cells = loss of hearing
69
what is place theory ?
determination of sound frequency by CNS
different sound frequencies activate different regions of the basilar membrane
this goes back to our definition of representation --> specific neurons dedicate to a specific function or purpose
the place theory in hearing basically says that different parts of the basilar membrane in the cochlea respond to different sound frequencies --> many sections of the basilar membrane are tuned to specific frequencies - high,middle ,low
each area of the basilar membrane vibrates most strongly in response to a particular frequency as we stated before
70
why is this place theory important ?
cuz its also mirrored in the brain
where certain areas are dedicated to processing PARTICULAR SOUND FREQUENCIES
71
what activates specific neurons in the brainstem and auditory cortex?
represented and activated in response to SPECIFIC SOUND FREQUENCIESS
THATS WHY PLACE THEORY IS IMPORTANT
72
we said antero-lateral was which type of frequency?
low
73
postero medial?
high frequency
74
why this representation is important ?
allow us to distinguish between different pitches and tones in the sound we hear much like a map where each region has its own role or identity
It is significant for the brain to identify the most stimulated regions of the BM to process the information related to specific sound frequencies.
75
so how is the primary auditory cortex A1 tonotopically organized ?
just like basilar membrane :
Low freq= antero lateral
High freq = postero medial
76
are the neurons in the cortex uni or bi lateral?
bi
most neurons respond to BOTH EARSS
77
what is the function of higher auditory cortex?
interpret meaningful pattern --> speech, music, voices
78
function of Medial geniculate nucleus?
help filter and modulate before sending signals to cortex
79
how does sound reach the brain and get interperpreted - auditory projection pathway?
1- sound is perceived by organ of corti - spiral ganglion
2- transduced signal travels to the brain via COCHLEAR division of CN8 - auditory nerve
3- Vestibulocochlear nerve synapse with the COCHLEAR NUCLEI in the brain stem ( PONNSS)
4- cochlear nuclei send nuerons to synapse with SUPERIOR OLIVARY NUCLEUS
- majority of fibers cross contralateral to terminate in the Superior olivary nucleus
-small amount remain IPSILATERAL for binauarl integration occurs
5- lateral lemniscus asecnding tract carry auditory info from cochlear nuclei and superior olivary nucleus to INFERIOR COLLICULUS
6- the superior olivary nucleus send neurons to the inferior colliculus ( inferior colliculus play role in reflexes )
7- the signals is relayed to the thalamus -- Specifically the MEDIAL GENICULATE NUCLEUS - ( medial for music )
8- finally fibers from medial geniculate project in temporal lobe to the auditory cortex
so in summary :
CN8 --> cochlear nucleus ---> superior olivary nucleus --> inferior colliculus --> thalamus ---> primary auditory cortex
80
what is another destination for the collateral fibers?
RASSS
for startleness and alertness
81
what does binaural means?
relating to or involving BOTH EARS
82
Role of inferior colliculus?
reflex
83
mnemonic for pathway?
ECOLIMA
E- cranial nerve EIGHT
C- cochlear nuclei
O- superior Olivary nuclei
L- lateral leminsicus
I- inferior coniculi
M- medial geniculate nuclei
A- auditory cortex
84
detailed auditory projection?
1- impulses are generated in the cochlea pass through the SPIRAL GANGLION-- AUDITORY NERVE
- Sound signals generated in the cochlea first pass to the spiral ganglion before traveling through auditory nerve ( cochlear division )
2- Then to DOSRAL and VENTRAL cochlear nuclei of the MEDULLA where all fibers synapse
3- Majority ( not all ) pass to the opposite side to terminate IN THE SUPERIOR OLIVARY NUCLEUS
- while it may look like that fibers end on the same side in the picture, most of them actually CROSS OVER to connect with the CONTRALATERALLLL SUPERIOORR OLIVARY NUCLEUS on the opposite side
BUT REMEMBER SMALL AMOUNT GO TO THE SAME SIDE OLIVAROY NUCLE
85
what is the significance of the having some fibers go contralateral superior olivary nuclie and some going ipsilateral ?
it makes each auditory cortex receive from both ears
cuz from one ear will go ipsilateral and contralateral
86
how does each auditory cortex receiving from both ears help?
having few fibers stay on the same side help with sound localization and spatial hearing
by receiving input from both ears each side of the brain can compare slight difference in TIMING AND INTESNITYYYY of sounds between the two ears, this allows us to determine the direction and distance of sounds in our environment
like listening to a friend while listenting to noise noise in the traffic, we are able to distinguish which is which
87
continue pathway from superior olivary nuclei ?
1- passes upward through LATERAL LEMNISCUS
- some fibers terminate in nucleus of lateral lemniscus to Inferior colliculus ( for auditory reflexEs)
2- majority of fibers continue the pathway passes to medial geniculate nucleus of the thalamus by way of the auditory radiation to the auditory cortex located in the SUPERIORRRRRR GYRUUSSSS of temporal lobe
- FOR THE MAJORTIY THAT DOESNT END IN THE INFERIOR COLICULIS
3- many collateral fibers pass directly into the RAS of the brainstem --> activate entire nervous system in response to loud sounds
we said some terminate in RASS
88
what can worsen the aging process of hair cells?
high frequency sounds
89
quick overviiew of the whole pathway?
Organ of corti
spiral ganglion
auditory nerve - cochlear nuclei in medulla
many synapse in superior olivary nucleus ( some contra some ipsi )
through lateral lemnisicus to inferior colliculi ( some stop here )
to medial geniculate nucleus --> auditory cortex ( superior gyrus of the temporal lobe )
some collateral go to RAS
90
MNEMONIC for it?
Our Stereo’s Annoying! Can Someone Leave It Muted Already?!
Our: Organ Corti
Stereo’s: Spiral Ganglion
Annoying: Auditory Nerve
Can: Cochlear Nuclei
Someone: Superior Olivary
Leave: Lateral Lemniscus
It: Inferior Collicus
Muted: Medial Geniculate
Already: Auditory cortex
91
how does the aduitory reflex pathway start?
organ of corti :
sound causes hair cell activation
afferent signals travel through CN8
these signals reach the cochlear nuclei in the pons
92
what is the main pathway pathway after cochlear nuclei?
1- ASCENDING sound pathway :
goes to superior olivary nucleus
lateral lemniscus
inferior colliculus
MGN - thalamus
Primary auditory cortex
this is the normal hearing patwahy
93
what is the reflex Hub nucleus ?
superior olivary nucleus
cuz its the first one that receives signals from both ears ( We said some contra and some ipsi!!)
94
what are 2 reflexes?
tympanic attentuation reflex
Head turning reflex
95
purpose of the tympanic attentuation reflex?
protect inner ear from loud sounds
96
what happens in tympanic attentuation reflex?
Both muscles in the ear contract and tense the tympanic membrane
Reducing the intensity reaching the cochlea = lower amount of sound perceived
97
what is the nerve supply for these muscles of the ear?
stapedius =facial
tensor tympani = mandibular v3
so we need to activate these 2
98
what is the pathway for tympanic attenuation reflex?
We start at Superior olivary nucleis
1- send motor signals to : tensor tympanic and stapedius
2- these muscles contract reflexively
3- they stiffen the ossicular chain and tympanic membrane
4- result in reduced sound transmission protecting the cohclea
99
what is the location of superior olviary nuclei?
pons
and both V3 and facial nucleis are in the pons as well
99
when does the tympanic reflex activate?
loud noise
your own voice - prevent damage from your own speaking
100
what is the purpose of head turning reflex?
help locate and orient toward the sound source
101
pathway of head turning reflex?
we start at superior olive nucleus as well :
1- inferior colliculus ( midbrain reflex center )
2- motor neurons to the neck muscles
3- rapid head turn toward the sound
this explains how sudden noise like dropped object or someone calling your name makes you turn instantly
102
what is the key reflex center in head turning reflex?
inferior colliculus
103
what extra loop we have in the pathway?
cochlear tuning
olivocochlear bundle
104
purpose of cochlear tuning ?
improves ability to distinguish speech from background noise
help reduce unwanted amplification
Enhances signal to noise ratio
this is a feedback control system
105
pathway of cochlear tuning pathway?
also start superior olivary nucleus :
1- send efferent fibers DOWN BACK TO COHLEAAAAAA ( cochlea send to superior olivary normally )
2- these fibers act on OUTER HAIR CELLLSSS and activate them
3- result in adjusting the sensitivity and sharpens tuning - improves clarity in noise
Again this is a feedback control system
106
so what are the reflexes in the auditory pathway?
sound goes up to brain through CN8 then at superior olive it branches:
1- path goes up for hearing
2- other path goes back down to fine tune cochlea
3- one path goes to ear muscles to protect it
4- one path goes to neck muscles to turn your head toward the sound
107
auditory cortex regions ?
like the Basilar membrane in which different regions are associated with particular sound frequencies
the primary auditory cortex in the temporal lobe is also TONOTOPICALLY ORGANIZED
PLACE THEORRYY
You can say the primary auditory cortex (in the temporal lobe) and the Basilar Membrane are tonotopically organized in perceiving sound. (Which, once again, means different regions exist to perceive different sound frequencies)
108
How is the auditory cortex mapped?
according to sound frequencies
specific cortical neurons are stimulated only in response to specific sound frequencies
High frequencies activate one area, and low frequencies activate another, creating a “map” of sound frequencies.
109
what nuclei are involved in processing auditory?
several ones of the brainstem
Medial geniculate nucleus of the thalamus
are involved in processing of the auditory signals
MGN- processing and modulating what enters the auditory cortex
110
function of higher auditory cortex?
integration of separated sound signals into a coherent and meaningful patterns
111
how many tonotpic maps are found in the primary auditory cortex and auditory association area?
6
112
where are low tones represented?
Antero lateralllyy
ALT
AL= antero laterally
LT= low tune
113
where are high tones represented?
Postero Medially
114
are neurons of auditory cortex uni or bi ?
bi
most neurons respond to inputs from both ears
115
what is the location of auditory association areas?
adjacent to the primary auditory receiving areas
they are widespread
116
what is deafness?
loss of hearing
wether temporary or permanent or partial or complete
can be congenital or acquired
117
types of deafness ?
its based on the dysfunction of hearing mechanism:
Conductive deafness
Sensorineural deafness
Neural prebyscusis
118
what is conductive deafness?
occurs when sound waves ARE NOT CONDUCTEDDD
sound cannot reach the cochlea
119
causes of conductive deafness?
physical blockage of the ear - EARWAX
Rupture of tympanic membrane - perforation
Middle ear infection - otitis media
Otosclerosis - ossicle fixation (limited movement of the ossicles )
120
what is sensorineural deafness?
occurs when the transmission of the sound to the inner ear is intact- sound can reach cochlea
but then a problem happens after that --> cochlea or nerve problem
damage to neural components of the auditory system AT ANY POINT--> After reaching the cochlea
Sound waves are not translated to nerve signals and NOT recognized as sound sensation by the brain
121
what can cause sensorineural deafness?
Hair cell damage
CN8 lesions
Noise trauma
Aging - presbycusis
Ototoxic drugs
122
what is neural prebycusis ?
Partial loss of hearing due to aging
by the age of 65 we lose more than 40% of cochlear hair cells
and loss of hair cells = loss of neuronsw
123
what disappear first in neural prebycusis ?
high frequencies- -> cuz basal cochlea is the most vulnerable- NEAR THE OVAL WINDOW
124
what differentiate neural presbycusis from other deafness types?
neural presbycusis is BILATERAL AND SYMMETRICAL
Physiology Year 3 SEM1
flashcards
Decks in class (15)
# Cards
-
ORAGNIZATION of nerves53
-
conduction system45
-
CSF physiology94
-
physiology of RASS84
-
brain waves86
-
basal gangli86
-
memory100
-
PHOTORECEPTORS88
-
cerebral blood flow75
-
neuro of retina109
-
Central processing of vision115
-
Vesti and equil part 199
-
Vesti and equil part 247
-
physiology of hearing108
-
processing of hearing125
