A&P Of Auditory System Flashcards
What does an vibrating object create?
Pressure waves
What happens if you are near enough to a vibrating object?
The air pressure at your ear changes
What is sound?
Changes in pressure over time
What happens to tuning forks vibrating at a high frequency?
They are stiff and light
What happens to tuning forks vibrating at a low frequency?
Flexible and heavy
Where do sound waves travel?
Through air
Mammalian sensory receptors are located where?
In an aqueous environment (the cochlea), which has a different impedance than air.
What happens Because of this ‘impedance-mismatch’ between the low density air and higher density water?
about 99.9% of the acoustic energy would lost (reflected) if sounds impinged directly on the fluids of the inner ear.
What are the areas of the outer ear?
Pinna
Ear canal
What does the pinna do?
acts as a directional filter, amplifying sounds from some directions more than others. Note that this effect is frequency- specific.
What is the wavelength of the resonant frequency (F0)?
4x the length of the tube
F0=?
Speed of sound/4*length
If a tube is 2.5cm long what is the F0?
Fo = c/4L
Fo= 344ms/4.025
Fo=~3400 Hz
Results in about a 10dB increase in a signal level.
What do the two major parts of the outer ear work together to increase?
the sound pressure level by up to 20 dB
What are the sections of the middle ear?
Tympanic membrane
Ossicles
Middle ear muscles
What is the are of the eardrum larger than?
That of the footplate at the oval window
What is the area of the eardrum?
55mm2
What is the area of the footplate?
3.2mm2
What does 20log(55/3.2) =?
25dB gain in sound pressure
The length of the manubrium is slightly greater that the length of what?
The inferior process of the incus
What is the lever ration in the inner ear?
1.3:1 (~2dB)
What are the contents of the inner ear?
Cochlea
What are the two sensory structures in the inner ear?
Vestibular apparatus
Cochlia
What does the Vestibular apparatus contain?
Sensory structures for balance and head movement
What does the cochlea contain?
Sensory epithelium for hearing, the organ of corti
What is the cochlea?
A three-chambered, tubular bony structure wound into a helix.
How many turns are in the cochlea?
3.5, 35mm long from base to apex
What is the central axis of the helix referred as?
The modiolus
How do vibrations get to the cochlea?
Oval window faces into the vestibule. Vestibule contains sensory epithelia for vestibular apparatus (saccule and 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
What does the Scala media contain?
Organ of corti
Stria vascularis
What is the organ of corti?
sensory epithelium containing the auditory hair cells.
What is the stria vascularis?
Regulates ionic and metabolic environment of scala media.
When do objects vibrate most strongly?
At their resonant frequency
What determines an objects resonant frequency?
The mass and stiffness
Fs=sqrt(s/m) explain
Square root of stiffness divided by mass equals the resonant frequency
What happens with increasing stiffness?
Frequency goes up
What happens with increasing mass?
Frequency goes down
Describe the basilar membrane ends
• Stiff and light at one end
• Flexible and heavy at the other end
Does the resonant frequency change over length?
Yes
The basilar membrane is populated with what?
Hair cells
What are hair cells the origin of?
Epithelial origin
What do hair cells resemble?
The cells that line the stomach
What does sterocilia form?
A bundle at apical pole of the hair cell.
What do inner hair cells turn vibrations into?
Neural signals
What do outer hair cells do?
Amplify vibration
When are outer hair cells motile?
When stimulated, outer hair cells change their shape and stiffness.
What do hair cells act as?
amplifiers, increasing the amount of vibration on the basilar membrane.
What does basilar membrane motion transmit? What is the result of this?
forces to move hair cell bundles, this changes the receptor potentials of the outer hair cells.
What happens when the receptor potential changes?
makes outer hair cells change shape
What do outer hair cell shape changes generate?
generates force that feeds back onto the basilar membrane, amplifying its vibration
What happens if outer hair cells are lost?
vibration isn’t sufficiently amplified.
What happens if inner hair cells are lost?
means no signal to the brain.
What are all hair cells vulnerable to?
noise, infections, aging, certain drugs, and just plain wear and tear.
Where is the tonotopic map maintained?
through much of the central auditory system.
What does path length differences cause?
interaural time difference
What does a head shadow cause?
interaural level differences
What may be ambiguous when on their own?
ITD and ILD
What do the head, pinna and ear canal act as?
a directionally- dependent spectral filter.
What is head related transfer function?
The pressure gain measured at the ear as a function of source location and frequency.
Head related transfer functions are specific for what?
specific locations in space.
In vertical plane, spectral notches are associated with what?
Specific elevations
What does HRTF heavily dependant on?
The shape of the ear
Are some sources of hearing loss addressable?
Yes
Is hearing a fragile sense?
Yes
How can you protect you hearing?
With ear plugs or defenders
Why should you drink tea and eat blueberries?
evidence suggests that antioxidants may help preserve your hearing.
What do The physical properties of the outer and middle ears help?
sound vibrations to pass into the inner ear.
What does The heavy/compliant → light/stiff gradient along the basilar membrane mean?
that different frequencies cause it to vibrate most strongly in different places.
Vibrating inner hair cells causes them to what?
Send neural impulses along the auditory nerve
What does Vibrating outer hair cells do?
strengthens the vibration of the basilar membrane. This is the basis of the cochlear amplifier.
The arrangement of frequencies in the cochlea is maintained into what?
the central auditory system all the way up to primary auditory cortex. This is referred to as the tonotopic map.
