Hearing

Question 1

overview of process

Answer 1

Sound waves are collected by the pinna, which is the visible part of the outer ear, and funneled into the ear canal.

The sound waves cause the eardrum (or tympanic membrane) to vibrate, which in turn causes the three tiny bones of the middle ear (the malleus, incus, and stapes) to vibrate as well.

The vibration of the stapes bone causes a fluid-filled structure called the cochlea to vibrate. The cochlea is the organ responsible for converting sound into electrical signals that can be interpreted by the brain.

Within the cochlea, there are thousands of tiny hair cells that are responsible for detecting the vibration caused by the sound waves. When the hair cells move, they generate electrical signals that travel up the auditory nerve to the brain. Scala vestibuli and scala tympani move the basilar membrane

The auditory nerve carries the electrical signals to the brainstem, where they are processed and interpreted. From there, the signals travel to the higher regions of the brain, where they are further processed and perceived as sound.

Question 2

Basilar Membrane

Answer 2

• contains hair cells with stereocilia tethered to tectorial membrane
• Basilar membrane vibration bends stereocilia
• Opens ion channels -> depolarizes hair cell -> triggers nerve impulse in nerve fiber
  Changes something mechanical to electrical transduction

Question 3

how do inner hair cells trigger an action potential?

Answer 3

vibrations of basilar membrane bend hair cell called stereocilia in tectorial membrane
Increase tension in tip links on tips of stereocilia

Ion channels open
Potassium and calcium ions rush in
Depolarize cell
Influx of Ca2+ ions at base of cell
Transmitter release (glutamate)
Trigger action potential in afferent nerve

Question 4

what is the tonotopic mapping of the basilar membrane

Answer 4

• Regions of basilar membrane only move if sound is
  specific frequency (elasticity differences along length)
• Hair cells in specific region respond to specific
  frequency
• Base = narrow/stiff = responds to higher frequencies
• Apex = broad/floppy = response to lower frequencies

Question 5

outer hair cells

Answer 5

Cell body elongates and contracts along with sound
Help both amplify and tune signal
How to have feedback to help transduce sound more efficiently
How? They adjust basilar membrane displacement
How does movement occur? Voltage within membrane activates the amplifier motor protein prestin

Question 6

the prestin gene is associated with

how does aspirin affect prestin

Answer 6

deafness

aspirin overdose inhibits prestin

Question 7

Sensorineural deafness

Answer 7

damage to organ of corti (e.g. hair cells)
Infection, toxins, trauma, exposure to loud noise
Permanent hearing loss (could we regrow damaged hair cells?)
Ability of auditory nerve to conduct action potential is often preserved

Question 8

what is the signal for hearing

Answer 8

changes in pressure waves
mechanical energy caused by the vibration of matter. there are increases and decreases in air pressure. so compression and expansion of air molecules produce sound

Question 9

what does amplitude mean for sound

Answer 9

indicates loudness

high amplitude = louder
low amplitude = quieter

If the amplitude is too high, you start getting hearing damage

Question 10

what does frequency mean for sound

Answer 10

Frequency: (cycles per second) Is what represents pitch - how high or low sound is

Question 11

what is the restricted range or responsiveness?

Answer 11

is the range of sound an individual can hear

Ex: elephants can hear lower frequencies
audible range for humans = 20-20k Hz

Question 12

how does the transmission of sound waves occur?

Answer 12

1. sound wave comes in through ear
2. tympanic membrane vibrates in response to sound wave
3. vibrations are amplified across ossicles
4. vibrations against oval window set up standing wave in fluid of vestibuli
5. pressure bends the membrane of the cochlear dict ata point of maximum vibration for a given frequency causing hair cells in the basilar membrane to vibrate

Question 13

what is the cochlea

Answer 13

coiled, fluid-filled structure in the inner ear
Transduce sound energy into neural activity
Contains primary receptor cells (hair cells. Are embedded in basilar membrane)

Question 14

what is the oval window

Answer 14

Where sound goes from middle to inner ear (ossicles are transforming mechanical energy to tympanic membrane)
It sends signal through different chambers of cochlea

Question 15

what is the basilar membrane and what is its influence in how sound is transmitted to the brain?

Answer 15

• vibrates in response to sound
• contains hair cells with stereocilia tethered to tectorial membrane
• Basilar membrane vibration bends stereocilia (which is what actually bends from sound)
• Opens ion channels → depolarizes hair cell → triggers nerve impulse in nerve fiber
  Changes something mechanical to electrical transduction

Question 16

how do the inner hair cells work to send sound signals?

Answer 16

Vibrations of basilar membrane bend hair cell stereocilia in tectorial membranes increase tension in tip links on tips of stereocilia causing the ion channels to pop open → Potassium and calcium ions rush in which depolarizes cell causing → influx of Ca2+ ions at base of cell which then causes → transmitter release (glutamate) ultimately → Triggers action potential in afferent nerve

Question 17

The Basilar Membrane has Tonotopic mapping. What does this mean and what part is related to which kind of frequency (high vs low)?

Answer 17

Regions of basilar membrane only move if sound is at a
specific frequency (elasticity differences along length)

Hair cells in specific region respond to specific frequency
* Base = narrow/stiff = responds to higher frequencies
* Apex (center) = broad/floppy = responds to lower frequencies

Question 18

what is place coding in the basilar membrane?

Answer 18

Pitch encoded in physical location of activated receptors along length of basilar membrane
Base = high frequencies = treble
Apex = low frequencies = bass

Question 19

What do outer hair cells do and how?

Answer 19

Cell body elongates and contracts along with sound
Help both amplify and tune signal
How to have feedback to help transduce sound more efficiently
How? They adjust basilar membrane displacement

How does movement occur? Voltage within the membrane activates amplifier motor protein. Motor protein: prestin (shorten/lengthens the outer hair cell)

Question 20

implications for hearing loss bc of prestin gene

Answer 20

• Mutations in Prestin gene in humans associated with deafness
• Aspirin overdose inhibits Prestin function

Knockout mice with alterations in
Prestin protein have less somatic motility
& demonstrate hearing deficiency

Question 21

sensorineural deafness

Answer 21

caused by damage to organ of corti (e.g.,, hair cells) from Infection, toxins, trauma, or exposure to loud noise for example
Leads to permanent hearing loss
Ability of auditory nerve to conduct action potential is often preserved

Question 22

How do cochlear implants work?

Answer 22

They directly stimulate the auditory nerve so it takes the sounds and sends it to the wire
Skips the NT part and directly stimulates the nerve
Limitations: only a certain number of electrode can be mapped onto the regions, so only a couple of frequencies can be transduced
Sounds can be warped, music does not sound as good sometimes

Question 23

overview of the primary ascending auditory pathway

Answer 23

Left and right ear sound signals cross. First hit the Cochlear nuclei in the brainstem (70% of the fibers cross to the opposite hemisphere). → Superior olivary nuclei inputs from both ears converge. (important for localizing sounds by comparing the sounds coming into both ears. Ex: loudness and timing differences bc one ear is closer than the other) → Inferior colliculi in midbrain where basic processing of sound is done → Medial geniculate of nuclei of Thalamus (which is top of brainstem). A lot of sensory information goes through this → projects info to the cortex

Cochlear nuclei → superior olivary nuclei → inferior colliculi → medial geniculate of nuclei of thalamus → auditory cortex

Question 24

cortical auditory networks

Answer 24

• Fronto-temporal (ventral) connections = “what”
  Ventral helps identify the what of the sound
• Parietal lobe (dorsal) connections = “where”
  Dorsal help think of where sound is in space

Question 25

what happens in amusia

Answer 25

Can hear sounds but can’t interpret them as music

Primary auditory cortex is fine, but they cant interpret it as music. The tract from primary auditory cortex to frontal cortex is impaired. (superior temporal gyrus and inferior frontal gyrus )

Question 26

how are motor areas and auditory systems interconnected? how is is used in Gait training in Parkinson’s disease?

Answer 26

Auditory and Motor systems being co-activated when listening to music to interpret it. Rhythmic music activates cortical and subcortical motor areas (premotor cortex, supplementary motor cortex, basal ganglia, and cerebellum)

Gait training in Parkinson’s disease: use music to help patients move. Rhythmic music activates mesolimbic and mesocortical dopamine pathway (pleasure and reward)

Question 27

what is auditory entrainment? how is this important for language comprehension

Answer 27

Pacemaker sets the rhythm frequencies of neural oscillations (Alignment of neural oscillations to frequency of auditory rhythms)

if there is an aligned frequency then you are more inclined to interpret a rhythm one way than another. helps brain predict and understand sounds as language

Question 28

Why might it be useful to know about broader networks engaged by auditory stimuli? what are the therapeutic implications?

Answer 28

EX: potential role of rhythmic entrainment and music therapy with ASD ppl
Using is as a predictive factor for Dyslexia