Title: BV4 / Modul 2 / Hörsel

Q: WHat is the hearing system mainly composed of?
A: Mainly composed of the external ear

Q: What is the middle ear composed by?
A: Middle ear composed of malleus, incus, stapes

Q: What does the inner ear consist of?
A: The cochlea

Q: What does the inner ear originate from?
A: Everything is blue becuase they originate from the same embryonic structure (the otocyst)

Q: What is similar between cochlea and vestibular system?
A: The cochlea and the vestibular system share similar properties

Q: What is the function of the middle ear?
A: The middle ear has a fucntion to transfer the sounds  that are in the ear and that will propagate towards the cochlea which in contrast is filled with liquids, bc of this there is change in the aucustic impedance - so about 98-99% of the energy that is carried in the soundwaves in the ear is lost when reaching the water fluids

Q: How much of the energy carried in the soundwaves is lost when reaching the fluid?
A: About 98-99% of the energy that is carried in the soundwaves in the ear is lost when reaching the water fluids

Q: What causes the change of acoustic impedance?
A: That the soundwaves go from travelling in air to liquids

Q: What is a consequence of the acoustic impedance?
A: As a consequence this is translating down to about 40 decibel loss in the sound intensity this is why terristial animals have engeneered a system to compensate for that loss of energy and change in the acoustic impedance

Q: WHich 2 effects are important in the middle ear?
A: - Lever effect
- Change of surface size from the tympanic membrane to the ovale window (ratio 20:1)

Q: How do the size of the membranes change in the ear (middle), and why is this important?
A: The surface of the tympanic membrane is very large and the energies that are transferred from here to the samll ovale wondow is over a ration of 20:1 in surface and this helps in transfering the energy and the force into a  greater system

Q: What is the effect of the differences in size of the membranes in the ear (middle)?
A: The waves hitting the tymanic membrane are transferred onto a smaller surface and this is why it is compensation for that loss of energy

Q: What is the lever effect dependant on?
A: It's
depending on the distance and the weight that is displaced

Q: Which things are acting as levers in the middle ear and what's their function?
A: We have three levers (bones) that are acting in conjuncton to help compensating for that loss in energy

Q: How are the bones in the middle ear attached?
A: - These 3 bones are th samllest bones in the body, they are tied up to differnt ligaments and muscles and help this movement to help maintain fluidity

Q: What is the most important part of teh middle ear?
A: The bones: Malleus, Incus, Stapes

Q: How many cavities does the cochlea contain?
A: - Vestibular duct
- Tympanic duct
- Cochlear duct

Q: What are the vestibular and tympanic ducts composed of?
A: Both are composed of the same liquid that we call the perilymph

Q: What is the liquid in the cochlear duct called?
A: Is enriched with another type of liquiud called the endolymph

Q: What is the main idea of teh shape of the cochlea?
A: The main idea is that if u can fold this into a very long snail shape- if u undfold the snail u can see that the cavities of the vestibular and tymanic duct are relayed on to each other trough the end of it which is the helicotrema

Q: What is the top and the thickest most outer part of the cochlea called?
A: The top of the cochlea we call the apex and the thickest most outer part is the base

Q: How are the frequencies arranged in teh cochlea?
A: The frequencs are arranged in what we called a tonotopic gradient where the higher frequencies are located at the base of the cochlea and the lower frequences are at the apex

Q: Where are trhe higher frequencies located in the cochlea?
A: The
higher frequencies are located at the base of the cochle

Q: Where are the lower frequencies located in the cochlea?
A: The
lower frequences are at the apex

Q: What is the cochlear duct marked by?
A: The cochlear duct is marked with one lined/finelined membrane - which is the basilar membrane

Q: What do we have in the cochlear duct?
A: In
the cochlear duct we have a sensory epithelium which harbours the sensory
haircells

Q: How are the sensory haricells in the sensory epithelium in the cochlear duct connected?
A: These are connected with a bunch of neurons called the spiral ganglion nerves (spiral ganglion because of the shape of the cochlea)

Q: What does the organ of corti contain?
A: - Inner hair cells
- Outer hair cells

Q: What do the hair cells in the organ of corti have on them?
A: The sensory haircells have little bundles on top of them called stereocilia

Q: Where are the outer haircells of the organ of corti?
A: Outer haircells which are on the exterior/the periphery of the cochlea

Q: Where are the inner haircells of the organ of corti?
A: Inner hair cells are on the interior of the cochlea

Q: To what are the outer haircells attached?
A: Are attached to a membrane which is called the tectorial membrane

Q: What are the iner hair cells not connected to?
A: Are not connected to the tectorial membrane

Q: When will the bundles of the inner hair cells be stimulated?
A: They will be having their bundles being stimulated if the amplitude of the movements over the basilar membrane are sufficiently high so they will start shaping, moving up the stererocilia in different directions

Q: What else are the hair cells in teh organ of corti connected to?
A: The
haircells are connetced to different neurons and they propagate information
in higher relays in the brain

Q: What is the point of teh structure striae vascularis?
A: We have a range of cells from a structure called the striae vascularis (in scala media), because its highly vascularized

Q: What is the function of the striae vascularis?
A: The idea with this structure is that it sucks upp K+ from the blood and enriches the scala media/endolymph with this high K+ level

Q: What is the composition of the endolymph?
A: The
endolymph has one of the highest conc of K+ in the whole body (150mM), whereas
it is very low in Na+

Q: What is the composition of the perilymph?
A: In contrast perilymph is very low in K+ and very high in Na+

Q: What is the point of the high conc. of K+ in the endolymph?
A: The idea is having this very high level of K+ available in that cavity for the endolymph, is that it helps concentrating the K+ to such a level that atm the bundles of the haircells are sheered - we see that the channels are opening and the mekanosensory channels are opening  as well and the flow of K+ will be sucked into the cells, bc osmosis, and further relay the info into electric signals

Q: What happens to when the bundles of haircells are sheered?
A: The bundles of haircells are sheered - the channels are opening and the mekanosensory channels are opening as well, and the flow of K+ will be sucked into the cells, bc osmosis, and further relay the info into electric signals

Q: What does the high conc of K+ in teh endolymph trigger?
A: So, that very high konc. Of K+ is also triggering an endogenous potential taht is helping in the activation of the hair cells

Q: What can problems with hearing result from?
A: So when u have problems with ur hearing, these can result from issues with the hair cells functioning in the sprial ganglion neurons, but also problems in the stria vascularis

Q: What is the conc of ions in the endolymph?
A: - High K+ (150 mM)
- Low NaCl (1mM)

Q: What is the conc of ions in the perilymph?
A: - Low K+ (3mM)
- High NaCl (150 mM)

Q: What is the mechanical channels  not sensitive to?
A: - Not voltage sensitive
- Not ion sensitive

Q: What is the mechanotransduction of the haircells?
A: The mechanotransduction is a very fine and sensitive phenomenon bc these cells are not already very numerous in the system and these channels are in so low abundance so its been very hard to identify them

Q: How are the bundles of strerocilia arragned?
A: In
the contex of a hyperpolarization we can see first that the bundels of the
steroeocilia are in staircase shape and the channels that are fixed on the top
of the stereocilia are connetec to the top of the next stereocilia with a small
spring which we call a tip-link

Q: What is the tip link?
A: A small spring which connects the tips of the stereocilia of a hair bundle

Q: What is the tip-link composed of?
A: That tip-link is composed of differnet "caterine channels"  caterine proteins, and protein caterine which are acting like springs and help the channels be open when there is a deflection in the stereocilia

Q: How is a channel on the stereocilia opened or closed?
A: So the upper stereocilia is pushed away of forward and that closes or opens the cahnnel

Q: WHat happens when the tip-link is pulled?
A: When the tip-link is pulled like a spring this opens up the channel and this is when there is an influx of K+

Q: What else can there be an influx of whe the tip-links open the channels?
A: There can also be an influx of Ca2+ but we dont know if this is a key element in this mechanism

Q: What happens when there is hyperpolarization in teh stereocilia?
A: In the contex of a hyperpolarizataion all channels are closed and vesicles containing glutamate do not release transmittor

Q: What happens when there is depolarization in teh stereocilia?
A: Sheering of the
stereocilia in the outer (hair cells?) arrange there is an opeing in these channels, K+
flows in and there is a opening of ca2+-channels that causes the release of the
vesicles containing gluatmate and this is when neurotransmission happens

Q: Why don't the hair cells ahve a resting state?
A: Bc there is no absolute silence in the environment, so there is always a constant activity and that resting activity is kinda a mid-range(?) with which the haircells sometimes depolarise or hyperpolarise, and that movement of depolarization and hyperpolarization is matching the frequency of the sound stimulations

Q: What is hyper-/depolarization in the hair cells matching?
A: The movement
of depolarization and hyperpolarization is matching the frequency of the sound
stimulations

Q: What is an ex. of how the movement of depolarization and hyperpolarization is matching the frequency of the sound stimulations in the hair cells?
A: - So if u have 1 kilohertz stimulus you will have the movement of those sterocilia that will beat up at the frequenzy of 1 kilohertz and the subsequent release of the vesicles will also be at 1 kilohertz
- Then, higher regions from the base, meaning lower frequencies are then if we have 100 hertz frequency of stimulation, the same thing happens, the bundles will be moved at a 100 hertz frequency as well as the release of the vesicle

Q: What type of channel is there in the stereocilia?
A: Its a mecanical channel which doesnt close, its not voltage sensitive, not ion sensitive - it is ion permissive because K+ flows in, but its purely mechanic

Q: What are the sensory cells arranged/arrayed(?) in?
A: - Inner hair cells (rows on the top)
- Outer hair cells (stereocilia are formed into V-shaped structure)

Q: Where do we have cilia in the haircells?
A: We have top cilia, and lowest ones that are more  in the interior side of the haircell

Q: HOw can the stereocilia be damaged?
A: These cells can be damaged by different phenomena that can be sound exposure, ageing, medication (aminoglyecides, anticancer drugs (it can damage stereoculia, kill haircells and affect how stereoccilia are arragne which impacts our hearing) - there is no regeneration happening

Q: Can stereocilia of hair cells regenerate?
A: No

Q: What are the stereocilia of outer haircells attached to?
A: Outer
haircells which stereocilia is attached to the tectorial membrane

Q: What do the outer hair cells look like?
A: The outer haircells
are long and tubular and they have a pistant-like movement

Q: WHy do outer haircells have a pistant like movement?
A: This is becuase they contain a protein thats called prestine, one of the only proteins in the body that contracts upon electric stimulation - so, as soon as the stereocilia are stimulated by the upper movements

Q: What is prestine?
A: One of the only proteins in the body that contracts upon electric stimulation - so, as soon as the stereocilia are stimulated by the upper movements

Q: When does prestine contract?
A: Upon electric stimulation, so, as soon as the stereocilia are stimulated by the upper movements

Q: What does the basilar membrane do?
A: The
basilar membrane pushes up and down the stereocilia against the tectorial
membrane, which opens and closes up the channels which in turn will activate the
prestine protein in a frequency-locked manner - so in the same way the protein
will go up and down

Q: What does it result in that the basilar membrane pushes the stereocilia up and down against the tectorial membrane?
A: It opens up and closes the channels which in turn will activate the prestine protein in a frequency-locked manner - so in the same way the protein will go up and down

Q: What does contractions of outer haircells do?
A: The contractions of the outer haircells somewhat helps amplifying this oscillating movemnet (done by the basilar membrane) - it is only when this oscillation movement is ample enough that the bundles of inner haircells get stimulated and this is when inner hair cells starts propageating the information to the brain

Q: When do the inner hair cells become activated?
A: It is only when this oscillation movement from the contractions of outer hair cells, is ample enough that the bundles of inner haircells get stimulated and this is when inner hair cells starts propageating the information to the brain

Q: Which properties do neurons connected to the inner hair cells have?
A: The inner hair cells are connected with afference,
so the send info to the brain

Q: Which properties do neurons connected to the outer hair cells have?
A: The
outer haircells are connected to efference, so the get info from the brain to
evaluate is the sound too loud, not loud enough

Q: What happens if the sounds are too high (outer hair cells)?
A: If the sounds are too high there will be a compression mechanism that will avoid that sound from being amplified too high

Q: What happens if the sounds are too low (outer hair cells)?
A: If the sound isnt loud enough outer haircells help amplifying this, so there is very rapid feedback going on here

Q: What else do we call the outer hair cells?
A: Counter-amplifier mechanism - they can modify the loudness of the sounds

Q: What else are outer hair cells regulating?
A: They
are also regulating their own perception of intensity

Q: Why is it good that outer hair cells are regulating their own perception of intensity?
A: Because from
0 decibel to 120, note that this is a logarithmic scale, we cant have a linear progression in this there is somekind of dampening at the highest
loudness and the lower loudness levels (sigmoidal curve) - this is where the
cochlea is taking a large part of it

Q: HOw does sound enter the cochlea?
A: At the base the sound can enter the cochlea thorugh the ovale window and will propagate over the basiliar membrane until it recahes a stage of resonance

Q: Why do sounds enter the base of the cochlea?
A: Because if u have low freqcency the oscillation will stop at the apex of the cochlea, medium frequencies will stop in the middle and higher frequencies will stop at the base

Q: What happens when we have complex sounds entering the cochlea?
A: When u have complex sounds we have oscialltion throughout the whole length of the basilar membrane

Q: What makes the oscillation (of the basilar membrane) restricted to one position?
A: Gradient of stiffness

Q: How does the gradient of stiffness affect the base of teh cochlea?
A: We have a region in the base which is very ridgid, this is where the higher frequencies will start to resonate

Q: How does the gradient of stiffness affect the apex of teh cochlea?
A: At the apex we have a very sloppy membrane which stiffness is lower but allows low frequencies to start oscillating the basilar membrane in that area

Q: What is the frequencies in the apex?
A: Low frequency

Q: What is the frequencies at the base?
A: High frequency

Q: What are our ears able to catch?
A: Our ear is able to capture 1 hertz, which is roughtly the twelvthed of the difference between 2 keys on a piano, take 2 keys of white key and the dark keys next to each other our ear is able to distinguish a difference in sound which is 1/12 of that nuance here - so its very high precision

Q: DO we have lateral inhibition in the ear?
A: In the ear there is no system of lateral inhibition, systems like that we see in the visionary or olfactry system - here we are taking advantage of multiple physical aspects

Q: Which physical aspects are important for frequency coding?
A: - Basilar membaren stiffness
- OHC amplification
- Nerve frequency selectivity

Q: Whne will OHC react?
A: Outer
hair cells will react at the moment they are stimulated by the oscillation and
they will amplify this movement

Q: What would happen with the basilar membrane if we had no OHC?
A: If u consider the basilar membrane in absense of outer hair cells u see the light grey wave-oscillation, the amplitude of it is very small

Q: What happens with the oscillations of a cochlea with functional OHC?
A: In the ocillations of the cochlea with functional OCH there is an amplification of that oscillation at a particular frequency place

Q: What does CF mean?
A: CF- place means the characteristic frequency

Q: What do the OHC do if we have 1 kHz tone?
A: If u have a 1 kilohertz tone at that particulary freqencuy the OCH will react even more and amplify this movement so that there is an increased perception of that 1 kilohertz tone
- However this is not sufficinet to enable a very good freqency in deportation(?)

Q: What happens after the oscillation have been amplified by the OHC?
A: What is happening next is that we have a nerve frequency selectivity, there is a phase locking happening between the neurons and the haircells, that means that under the haircells that perceive a tone of 1 kilohertz we have neurons tat are responsive to a 1 kilohertz release of glutamate - the further we go away from that 1 kilohertz these neurons dont respond equally well, we ned much more louder stimulus in decibels to achieve their response

Q: What is the function of nerve frequency selectivity?
A: There is a phase locking happening between the neurons and the haircells, that means that under the haircells that perceive a tone of 1 kilohertz we have neurons tat are responsive to a 1 kilohertz release of glutamate - the further we go away from that 1 kilohertz these neurons dont respond equally well, we need much more/louder stimulus in decibels to achieve their response

Q: How do different neurons signal at differet frequencies? Explain the different graphs:
A: - So at this particular frecuenxy (low,1) u need very little stimulation for these to respond and send information to the brain that someting is hurt
  - The further u go from that region those neurons wont be able to capture that 1 kilohertz sound equally welll
- 3,5 kH thre is their characteristic frequency, but if we go down to 1 kilohertz, these neurons need about 50 decibel extra stimulation to start firing a respons towards the barin
- Yellow - we are at high frequencies, and the neuron here repsonds well to higher frequency, but at 1 kHz it needs 70 decibel to start sending info to the brain

Q: What does the frequency coding in hearing combine?
A: The frequency coding in hearing combines 3 different systems
- Basilar Membrane stiffness
- OCH amplification fo the sounds and thus the movements of the basilar membrane
- Nerve frequency selectivity, nerves that are underneith the haircells and are resonding in a frequency selective manner

Q: What happens on the stimulus way from cochlea to the brain?
A: When we go from the cochlea and propagate info to the brain there are several relays

Q: Which are the relays on the way from teh cochlea to teh brain (C.S. LIMA)?
A: - Cochlear nucleus
- Superior Olive complex
- Lateral lemniscus
- Inferior colliculus
- Medial geniculate
- Auditory cortex
C.S. LIMA
(to remeber them)

Q: What is meant by the fact that there is a persistance of the tonotropic gradient in the auditory cortex?
A: In the auditory cortex we have a persistance of this tonotopic gradient, meaning that from the cochlea were we have high frequencies in the base, low frequences in the apex, that array persists throughout the auditory pathway up to the auditory cortex

Q: Which regions do we have in the superior olive complex?
A: - LSO
- MSO

Q: What are the LSO and MSO important for?
A: They are
important for capturing differencens in sound intesities between the 2 ears

Q: What is the MSO responsible for?
A: Time changes
The MSO is responsible for detecting time differences, if the sound comes into ur left ear it will reach it before the sound affects the other ear and the MSO is repsonsible for detecting these small differences (milliseconds)

Q: What does the LSO detect?
A: Intensity of sound

Q: What does tinnitus result from?
A: Tinnitus results from a sensory deprevation in the same way that u have phantom sensation of an amputated hand in this case the brain is trying to compensate for the lack of sensory imput when there is none, the brain has a added detection to this and compensates with increasing the gain and perceives that the hand is still there although its not

Q: WHich cells are most often affected in tinnitus?
A: Most often the high frequency cells, so if they are missing the brain will start compensating for that missing sensory imput and push out the gain to try to capture these cells, this is whne suddleny a ficktive tone is generated in the brain but it doesnt exist physically - this is tinnitus

Q: What does tinnitus usually cause?
A: Usually it creates a wave of hyper activity all along the way of the auditory pathway and this is thought to be someting everybody sometimes experience in their lives

Q: Why do some people perceive tinnitus as very bothersome?
A: This
is bc there are interactions with other pathways like the somatosensory pathway
which propagates and joins the cochlear nucleus where it starts interacting on
the plasticity that is altered - this makes it louder

Q: What are ex. of regions that will interact with the auditory pathway and affect tinnitus?
A: Regions like the hippocampus and amygdala will also interact with certain regions of the auditory pathway and will make that excererbation

Q: What is the difference between hebbian plasticity and homeostatic?
A: Hebbian plasticity provides a synaptic basis for associative learning, whereas homeostatic plasticity serves to stabilize network activity