An overview of the anatomy and physiology of the auditory system. Flashcards
What is sound?
Sound is changes in pressure over time.
Any vibrating object creates ________ waves.
pressure
If you are near enough to a vibrating object , the _____ _________ at your ear _________.
Air pressure
changes
pressure changes happen all the time but it happens so ________ that we can’t hear the sound.
slow
We hear “sound” only in a certain ______ of _________.
Range, vibrations.
What is resonant frequency?
A frequency something likes to vibrate at.
Every Object has a ______ frequency.
resonant.
What is the auditory system’s role?
To distinguish between the complex mixture of low frequency and high frequency sounds.
Where do sound waves travel?
Through the air.
Mammalian sensory receptors are located in an __________ environment.
aqueous
Because the cochlea is fluid and sound waves travel in air- what does this create?
an impedance mismatch
If we only had an inner ear- with impedance mismatch, what would happen?
99.9% of acoustic energy would be lost (reflected).
Name the parts of the Outer Ear.
Pinna Ear Canal (auditory meatus)
What is the role of the outer ear?
To focus sound down and into the ear canal.
What does the pinna act as?
A directional Filter.
The pinna acts as a directional filter and __________ sounds.
amplifying.
When we turn our head to the side, the sound can be __________.
Amplified.
The ear canal results in what?
This resonance along the tube results in about a 10dB increase.
The ______ and ________ amplify pressure at the ear drum.
pinna
ear canal
How much does the outer ear increase the sound pressure level by?
20dB.
What can go wrong in terms of the outer ear?
- malformation or missing outer ear
- obstruction in ear canal (like wax)
Name the parts of the middle ear.
- Tympanic membrane
- Ossicles
- Middle ear muscles
- Eustachian Tube
What are middle ear muscles attached to?
The ossicles.
Why would the middle ear muscles contract?
As a reflex to protect hearing.
What would change the resonant frequency of the ear?
Obstruction in ear canal (like wax). It moves the resonant frequency away from range of speech.
There is increasing ______ in the middle ear.
Pressure.
Why is there increasing pressure within the middle ear?
The area of the eardrum is larger than that of the footplate at the oval window- squeezes same amount into a smaller space, increasing the pressure.
The length of the ______ is slightly greater than the length of the inferior process of the _________. What does it increase and what does it act as?
Manubrium
Incus
Increases pressure by 2 dB
Acts as a lever.
From the tympanic membrane to the oval window, there’s a ______ dB gain in sound pressure.
25
What can go wrong in the middle ear?
- malformed or missing ear bones
- dampened vibration due to fluid build up.
What does malformed/missing ear bones result in?
Loss of amplification (25 dB).
When the middle ear is filled with fluid, what is this called?
Glue ear.
How does glue ear affect hearing?
It’s harder for the bones to vibrate, missing out on the amplification.
What makes up the inner ear?
- Oval Window
- Vestibular Apparatus
- Cochlea
- Semi-circular canals
What’s the fancy name for the ear canal?
Auditory Meatus.
Whats the fancy name for the auditory tube?
Eustachian Tube.
The inner ear has 2 sensory structures, name these.
- Vestibular Apparatus
- Cochlea
What does the vestibular apparatus contain?
It contains sensory structures for balance and head movements.
What does the cochlea contain?
It contains sensory epithelium for hearing; the organ of corti.
Name this-
A 3 chambered, tubular bony structure wound into a helix.
Cochlea.
The central axis of the helix of the cochlea is referred to as what?
The modiolus.
Describe how vibrations get into the cochlea.
- Oval window vibrates the vestibule (contains sensory epithelia for the vestibular apparatus- saccule & utricle).
- Vestibule leads into the scala vestibuli (upper duct of the cochlea)
- Waves of pressure pass through the scala vestibuli and back out through the scala tympani (lower duct of the cochlea), terminating at the round window.
The saccule and utricle make up the _____ ________.
Vestibular apparatus.
What is the upper duct of the cochlea called?
The scala vestibuli
What is the lower duct of the cochle called?
The scala tympani.
What is the scala media part of?
The cochlea.
What does the scala media include?
- Organ of Corti
- Stria Vascularis
What is the organ of corti?
Sensory epithelium containing the auditory hair cells.
What regulates the ionic and metabolic environment of scala media?
Stria Vascularis.
The organ of corti is __________ of _____ ___________.
Rows, hair cells.
What are the hair cells in the organ of corti connected up to?
Nerve Fibres.
Objects vibrate most strongly at their ______ _______________.
Resonant Frequency
What determines the resonant frequency of an object?
The mass and the stiffness of an object.
Resonant frequency goes up with ______ stiffness.
Increasing.
Resonant frequency goes down with _________ mass.
Increasing.
What would an object be if it had a high resonant frequency?
It would be stiff and light.
What would an object be if it had a low resonant frequency?
It would be loose and heavy.
What structure in the inner ear is used to separate low from high frequencies?
The basilar membrane.
What membrane sits above the organ of corti?
Tectorial membrane.
What membrane sits below the organ if corti?
Basilar membrane.
Describe the basilar membrane.
It’s stiff and light at one end, and flexible and heavy at the other end.
The basilar membrane’s ____ _________ changes over it’s _____________.
resonant frequency
length
If a low frequency tone is played, what part of the basilar membrane will vibrate?
The loose and heavy end.
If a high frequency tone is plays, what part of the basilar membrane will vibrate?
The stiff and light end.
What is the basilar membrane populated with?
Hair cells.
The basilar membrane is part of the _______.
Cochlea.
What are the hair cells in the basilar membrane responsible for?
For tuning vibration into something the brain can understand.
Hair cells are of ________ origin and resemble the cells that line the _________.
Epithelial
Stomach
What form a bundle at the apical pole of the hair cell?
Stereocilia.
What are stereocilia?
Stereocilia are at the tops of hair cells.
Stereocilia have thread at their tips. What are these called?
Tip links.
A cell is stimulated, the current rushes in, changes the ________ and travels along the _________.
Voltage, Neuron.
An action potential is always the _________.
Same.
An _______ potential is either triggered or not.
action.
What is the currency/language of the brain?
Neurotransmitters.
At the end of the neuron, what is released and what does this cause?
Neurotransmitters are released and this causes the next neuron to let chemicals in.
Hair cells are stimulated, what does this cause the stereocilia to do?
To move in one direction- causing a change in the firing rate.
Depolarisation _________ impulse frequency whereas hyperpolarisation ________ impulse frequency.
increases
decreases.
An inner hair cell has lots of _________ fibres, why?
Afferent.
To take information to the brain.
An outer hair cell has few connections to the ___________. It has more _____________ fibres,why?
brain
efferent, takes information from the brain.
What is the role of inner hair cells?
They turn vibrations into neural signals.
What is the role of outer hair cells?
They amplify vibration.
When activated/stimulated what happens to the outer hair cells?
They change shape and stiffness.
Outer hair cells are ________.
Motile.
Outer hair cells act as ______, increasing the amount of _________ on the basilar membrane.
Amplifiers
Vibration.
Outer hair cells can move the _______ and __________membranes up or down.
Tectorial, basilar.
___________ ___________ motion transmits forces to move hair cell bundles. What does this change?
Basilar membrane
It changes the receptor potentials of the outer hair cells.
Changing the receptor potential makes outer hair cells….
Change shape.
What happens when the outer hair cells change shape?
It generates force that feeds back onto the basilar membrane, amplifying its vibration.
______ hair cells don’t touch the tectorial membrane.
inner.
What does the loss of outer hair cells mean?
It means that vibration isn’t amplified.
What does loss of inner hair cells mean?
It means there will be no signal to the brain.
What would cause more hearing loss- outer or inner hair cells being lost?
Inner- as they communicate with the brain!
What are hair cells vulnerable to?
Noise Infection Aging Certain drugs Wear and Tear.
What hair cells are known as boogie cells?
outer hair cells.
What structure is responsible for encoding speech?
The basilar membrane.
Name the 2 codes within pitch representation.
- place code
- temporal code.
What is place code?
The vibrations to a certain area of the basilar membrane tell us about the pitch.
What is a limit to the place code?
The vibration spreads a bit along the basilar membrane so it isn’t very accurate/concise.
What is temporal code?
Low and high frequency causes spikes of activity in the stereocilia. They fire in sync with the frequency.
What is the limit of the temporal code?
It doesn’t work at high frequencies- too fast so the neurons can’t keep up (due to the refractory period before they can fire again).
As both encoding systems have limits this is why…
They work together in parallel.
Central representation of sound frequency tells you about what?
It tells you about the frequency response area, in other words the specificity of the cell.
The central representation of sound graph tells us what?
How accurate hearing is. (what frequencies we hear).
We should have a small _____ and a ______ length on the central representation of sound frequency.
Width
Long
Although a hearing aid ampifies sound, what can’t it do?
It doesn’t give back any accuracy in picking up the different frequencies (receptive field can’t be narrowed)- so it will be louder but may still sound “muddy”.
What happens with age?
- neurons have higher thresholds
- receptive fields widen (gets less specific)
What could an old person have problems with in regards to central representation of sound frequency?
telling the difference between [g] and [b].
The central processing of sounds requires…
Lots of processes.
The organ of _____ is involved in _________ ________ of sounds.
corti
central processing
The ___________ map is maintained through much of the central auditory system.
Tonotopic.
Where is the tonotopic map?
In the primary auditory cortex.
Explain what the tonotopic map is.
The primary auditory cortex has a specific area for a specific frequency of sound.
When the sound source is right in front of you what happens?
The sound arrives at the same time to both the Left and Right ear, as it travels the same distance.
If the sound source is to the right- the sound takes longer to reach the _____ ear and shorter to reach the _____ ear.
left
right
If it doesn’t take the same time for a sound to reach the L and R ear, what is this called?
Interaural time difference.
What does interaural time difference help us tell?
It helps us to tell where the sound comes from.
The head creates a ______ _______ that causes inetraural ________ differences.
Head shadoe
LEVEL
What is the term for thinking the sound is coming from behind, when it is actually in front?
Front-Back Confusion
__________ and ______________ cues on their own may be ambiguous and lead to front back confusion.
Interaural Time Difference
Interaural Level Difference
When the head blocks high frequency sounds, what is this called?
A head shadow.
What is a filter?
It takes away a specific frequency of sound.
What does does a low pass noise take away?
High Frequency.
What does does a high pass noise get rid of?
Low Frequency
What does a band pass noise filter do?
It takes away high and low frequencies, leaving a little band of middle frequency left.
If a tamber is applied you get ______ noise.
Shaped
The head, pinna and ear canal act as a what?
They act as a directionally dependent spectral filter.
How do the head, pinna and ear canal act as a directionally dependenr spectral filter?
They apply a different filter (certain tamber to them) so we can tell what direction the sound is coming from.
Name this:
The pressure gain measured at the ear as a function of source location and frequency.
The head-related transfer function (HRTF)
HRTFs are specific for specific ______ in space.
locations.
Everyone filters sound _______, why?
Differently
Because everybody has a slightly different ear shape- unique to them (kinda like a fingerprint)
______ _______ strip out HRTF so the sound doesn’t sound as natural.
Hearing aids.
HRTF is heavily dependent on…
The shape of the ear.
Sound localisation is useful for what specifically?
For conversation eg. being able to focus on person on Right and ignore person on left.
Name an addressable source of hearing loss.
Wax in the ear- as wax can be removed.
What is a source of hearing loss that we can’t address?
Hair cell loss- once they are gone, they are goneeee :(
When the receptive field broadens what happens?
Sound clarity is reduced.
Hearing is a ______ sense.
Fragile
What do the physical properties of the outer and middle ear help to do?
They help sound vibrations pass into the inner ear.
The heavy/compliant > light/stiff gradient along the _______ _______ means that different frequencies cause it to _______ most strongly in ___________ _______________.
Basilar membrane
vibrate
different places
Vibrating inner hair cells causes them to send ______ _________ along the ___________ _____________.
Neural Impulses
Auditory Nerve
Vibrating outer hair cells strengthens the….
vibration of the basilar membrane.
What is the basis of the cochlear amplifier?
Outer hair cells.
The arrangement of frequencies in the cochlea is maintained into the ___________________ __________________ ______________________ all the way up to the _____________________________ _________________ _____________________. hat is this referred to as?
Central auditory system
primary auditory cortex
Tonotopic Map
