Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
116 Cards in this Set
- Front
- Back
|
What is sound?
|
Longitudinal waves of air that consist of periodic pressure fluctuations.
|
|
|
How do soundwaves bouncing compare to a golfball bouncing on a table?
|
Sound waves are perfectly elastic; oscillate indefinetely
Golfballs are not perfectly elastic; they will come to rest when dropped on a table. |
|
|
First part of hearing:
|
impingement of the wave's pressure and relaxation on the eardrum.
|
|
|
What is the Amplitude of a sound wave?
|
Its physical correlate of loudness
|
|
|
Pressure
|
F/A - Newtons
|
|
|
Energy
|
Fxd - Joule
|
|
|
Power
|
Energy/time
|
|
|
Intensity
|
Power/area
|
|
|
What does intensity take into account?
|
Force, time, and area
|
|
|
What are the characteristics of high intensity soundwaves?
|
-High force
-Short time -Little area |
|
|
What is the result of a high intensity sound wave?
|
Loud sounds
|
|
|
What is the unit of measurement for sound intensity?
|
The decibel
|
|
|
What is Reference intensity?
|
The softest sound that can be heard by normal adults; the threshold of hearing.
|
|
|
Why is sound measured in decibels?
|
Because as sounds get louder the perceieved loudness increases LOGARITHMICALLY.
|
|
|
Why do we care about measuring sound?
|
Because decibels is how we measure hearing loss.
|
|
|
What is the equation for measuring decibels?
|
dB = 10log(I/Io)
dB = 20log(P/Po) |
|
|
how is intensity related to pressure?
|
I = P^2
|
|
|
How much louder are two stereos blaring at 1 dB each than 1 stereo blaring at 1 dB?
|
Doubling intensity raises loudness by 3 dB
|
|
|
what is the physical correlate of loudness?
|
Amplitude
|
|
|
What is the physical correlate of pitch?
|
Frequency
|
|
|
What is the range of human sensation of frequency?
|
20-16000 Hertz
|
|
|
What is a Hertz?
|
Cycles/second
|
|
|
What are the components of the outer ear?
|
1. Pinna
2. External auditory canal |
|
|
Function of the pinna:
|
Shapes the frequency distribution to LOCALIZE SOUND - modifies it from different directions.
|
|
|
What is the function of the external auditory canal?
|
It is the resonant cavity - it amplifies sound at a given frequency.
|
|
|
How much is sound amplified by the external auditory canal at a frequency of 2.5 kHz?
|
by 15-20 dB
|
|
|
How much does sound intensity increase based on an increase in amplitude of 15-20 dB?
|
30-130 X the original intensity
|
|
|
What happens if the external auditory tube is SHORTER?
|
You can hear higher frequency sounds - dogs can hear dog whistles b/c they have short tubes.
|
|
|
What happens if the external auditory tube is LONGER?
|
You can hear lower frequency sounds.
|
|
|
What is the general function of the middle ear?
|
Mechanical
|
|
|
3 important components of the middle ear:
|
1. Tympanic membrane
2. Oval window 3. Apparatus for coupling sound energy from tympanic membrane to oval window. |
|
|
What is the tympanic membrane?
|
The eardrum at the lateral boundary of the middle ear.
|
|
|
What is the oval window?
|
The medial boundary (innermost) of the middle ear.
|
|
|
What is the apparatus that couples sound energy from the tympanic membrane to the oval window?
|
The ossicle apparatus
|
|
|
What are the ossicles?
|
Bones:
-Malleus -Incus -Stapes |
|
|
What is the function of the ossicles?
|
Coupling of sound waves impinging on the tympanic membrane to the cochlea for sound transduction.
|
|
|
Where does the stapes terminate?
|
On the oval window - the beginning of the cochlea
|
|
|
What else is in the middle ear other than bones?
|
Muscles:
-Tensor tympani -Stapedius |
|
|
Which muscle is more important?
|
Stapedius
|
|
|
Why is the stapedius important?
|
Because when it contracts it reduces sound transmission by about 10 dB
|
|
|
Why does the middle ear attenuate sound energy?
|
To protect the ear from damage.
|
|
|
What is the mechanism of the stapedius and tensor tympani called?
|
The attenuation reflex
|
|
|
How does the attenuation reflex work?
|
When a person hears a loud sound the muscles tighten and keep the bones from moving - impedes energy transfer to cochlea.
|
|
|
What would it be like if you lacked the attenuation reflex?
|
Loud sounds would feel like someone jumping on your back
|
|
|
What is the attenuation reflex not good for?
|
Protecting against sudden loud sounds - because of its reflex time - takes .25 sec to occur.
|
|
|
What principle needs to be accounted for in transferring energy from the tympanic membrane to the cochlea?
|
Impedence - going from low impedence of air to higher impedence of cochlear fluids.
|
|
|
What is the acoustic impedance transformer principle akin to?
|
Belly flopping - easily move through air, then all of a sudden hit the water and whack you're impeded a lot more.
|
|
|
What eases the impedence transformation during a dive?
|
if you turn your body so that it has less surface area impacting the water surface.
|
|
|
What are the 3 principles used by the middle ear ossicle apparatus to couple sound energy from the tympanic membrane to oval window impedence transformer?
|
1. Hydraulic effect
2. Lever action 3. Buckling motion |
|
|
What is the hydraulic effect?
|
going from larger area of tympanic membrane to lower area of oval window -> greatly increases the pressure exerted per unit force.
|
|
|
What is the lever effect?
|
-Decreased Distance/time for F mvmt
-E is constant -Increased Force transferred. |
|
|
What does the Buckling motion contribute to impedance transformation?
|
Buckling decreases the velocity and size of movements and hence amplifies Force at the oval window.
|
|
|
How much does the external acoustic canal increase force?
|
100X
|
|
|
How much does the hydraulic effect increase force?
|
35X
|
|
|
How much do the buckling and lever effects increase force?
|
3X
|
|
|
So how much is the pressure of sound increased when it hits the oval window?
|
10000 times
|
|
|
What happens when the ossicles are broken and this sound amplification can't occur?
|
There is a 40 dB reduction in hearing at 2500 Hz.
|
|
|
How much more intense does sound have to be to be able to just hear it?
|
10000 times higher.
|
|
|
What does the inner ear consist of?
|
The cochlea
|
|
|
What is the cochlea?
|
A very tightly coiled, fluid-filled chamber that is embedded in bone.
|
|
|
Divisions of the cochlea:
|
Scala vestibuli
Scala media Scala tympani |
|
|
What is the scala vestibuli?
Where does it terminate? |
The upper chamber; terminates at the oval window where the footplate of the stapes is.
|
|
|
What is within the scala vestibuli and what is it like?
|
Perilymph - similar to ECF in composition.
|
|
|
What does the scala vestibuli communicate with and how?
|
With the scala tympani at the helicotrema - at the extreme end of the cochlea.
|
|
|
What is the scala media also called?
|
Cochlear duct
|
|
|
What does the scala media contain?
|
the transducer and endolymph
|
|
|
Endolymph is like what:
|
intracellular fluid - high in K and low in Na.
|
|
|
Where does the scala tympani terminate? What is its function there?
|
At the round window; functions to alleviate the pressure that occurs when the oval window is pushed in by the stapes.
|
|
|
What is contained in the scala tympani?
|
Perilymph - again similar to ECF in its composition.
|
|
|
What separates the Scala Vestibuli from the Scala media?
|
Reissner's membrane
|
|
|
What separates the Scala media from the Scala tympani?
|
Basilar membrane
|
|
|
What sits on top of the basilar membrane?
|
The organ of Corti - which contains the receptors for hearing.
|
|
|
Function of reticular lamina
|
forms a true chemical division between the ions in the endolymph of scala media and perilymph of scala tympani.
|
|
|
What membrane covers the organ of Corti? What is its structure like?
|
The tectorial membrane - a gelatinous and fibrous flap.
|
|
|
2 cell types that make up the organ of Corti:
|
1. Hair cells
2. Supporting cells |
|
|
What are the support cells for the organ of corti?
|
Glial cells
|
|
|
2 types of hair cells:
(what percentage is each?) |
Inner hair cells - 20%
Outer hair cells - 80% |
|
|
How many hair cells are there on average in man?
|
15000
|
|
|
What types of innervation is there to hair cells?
|
Afferents and Efferents (efferents not well understood)
|
|
|
Where are the cell bodies located for
-Afferents? -Efferents? |
Afferents - spiral ganglion
Efferents - superior olivary nucleus in brain stem |
|
|
What type of hair cells have more afferents?
|
Inner - even though they're lower in number, 95% of afferents contact them.
|
|
|
How many contacts with axon afferents does each inner hair cell have?
|
15-20
|
|
|
How many contacts with axon afferents does each outer hair cell have?
|
1; actually each axon branches to itself contact about 10 outer hair cells.
|
|
|
What type of axons contact inner hair cells?
|
Myelinated axons of bipolar cells
|
|
|
What type of axons contact outer hair cells?
|
Unmyelinated axons of unipolar cells.
|
|
|
How does the basilar membrane structure change going from the base to apex of the cochlear duct?
|
Base: narrow/rigid
Apex: wide/floppy |
|
|
What is the functional significance of the change in basilar membrane structure?
|
Base: more sensitive to high frequency sounds
Apex: more sensitive to low frequency sounds. |
|
|
How do we know that the basilar membrane responds differently to different sound frequencies at different areas on it?
|
Via Von Bekesy's experiments with cadaver cochleae.
|
|
|
What were Von Bekesy's observations?
|
1. High frequency tones produce waves that peak in displacement near the BASE
2. Low frequency tones produce waves that peak in displacement near the apex. |
|
|
What do we call the differential sensitivity to frequencies of the basilar membrane?
|
Frequency selectivity
|
|
|
What is the frequency selectivity of the basilar membrane like at SINGLE POINTS along it in a cadaver?
|
POOR
|
|
|
How do low frequencies move along the basilar membrane in a cadaver?
|
They travel all along the entire length of the membrane.
|
|
|
How do high frequencies move along the basilar membrane in a cadaver?
|
They move only near the base.
|
|
|
What is the frequency selectivity of the basilar membrane like at SINGLE POINTS along it in a live cat?
|
Quite selective - narrowly tuned
|
|
|
What does not cause the narrow tuning of a living cochlear neuron?
|
Lateral inhibition does not cause fine tuning!
|
|
|
What is responsible for the fine tuning of the basilar membrane in living cochleae?
|
Probably outer hair cells
|
|
|
Why do we think the OHC might be responsible for the basilar membrane's fine tuning?
|
Because when poisoned with kanamycin or furosemide the tuning curve is broadened.
|
|
|
What is a cochlear emission?
|
An echo generated by the ear in response to a sound
|
|
|
What is absence of cochlear emission caused by?
|
Sensorineural deafness
|
|
|
What is prolonged cochlear emission associated with?
|
Tinnitus (ringing in the ears)
|
|
|
What generates the echo that is Cochlear emission?
|
Outer hair cells, acting like little moters.
|
|
|
What do we call these outer hair cells?
|
the Cochlear Amplifier
|
|
|
How is it that OHC's can generate the cochlear echo?
|
They have motor proteins in their membranes.
|
|
|
What activates the motor proteins in OHCs? What is their response?
|
Potassium influx into the cells; activates them to lengthen.
|
|
|
How do outer hair cells cause echoing?
|
-Activation is caused by sound pushing on the basilar membrane; In turn the OHCs vibrate the membrane back and forth.
|
|
|
What allows outer hair cells to vibrate the basilar membrane?
|
Motor proteins activated by K influx into the cells.
|
|
|
How do OHC vibratory movements affect the basilar membrane?
|
Increase its bending and amplify the effect of mechanical vibration originally caused by the sound.
|
|
|
Where on the soundwave does the OHC motor activity magnify it?
|
At the POINT of maximal deflection - result is that frequency is MUCH more sharply tuned than if no OHCs.
|
|
|
How exactly do hair cells cause sound transduction into electrical signals?
|
Vibration of the basilar membrane and organ of Corti result in hair cell stereocilia bending.
|
|
|
What happens when stereocilia bend?
|
Depends on the direction of bending; one way results in depolarization; the other way results in hyperpolarization.
|
|
|
What happens when hair cells hyperpolarize or depolarize?
|
It changes the amt of NT released by the cells.
|
|
|
What does NT release from stereocilia do?
|
Activates the auditory nerve fibers.
|
|
|
Where exactly are the stereocilia located (between)?
|
Between the basilar membrane and tectorial membrane.
|
|
|
What happens when stereocilia bend at 90' right angles?
|
Nothing
|
|
|
How do stereocilia work together?
|
They are linked into TRANSDUCTION LINKS
|
|
|
When are stereocilia transduction links active?
|
When stretched
|
