LING330: Quiz #2 Flashcards
Outer ear (aka auricle)
Consists of:
1- pinna (visible shell of the ear)
2- tympanic membrane (ear canal leading down the eardrum)
Function of the pinna
Shell of the ear
Captures sound waves
Aids in localization
Function of ear canal
Keep eardrums safely inside our heads (shielded from changes in temp and humidity, and sharp objects)
Acts as a resonator (amplifies sounds especially in 3000hz range, crucial frequency area for speech sounds)
Why do we have two ears?
Locate sounds in space
Keep track of source of sound in a noisy enviro
Why is there a delay in time and intensity when a sound reaches one ear and the other?
Because they’re separated by a heads width and decrease in intensity is bc “shadow” of the head
How does the brain interpret location of sound source?
Sounds echo in folds of pinna in characteristic ways (depending on where sound is coming from)
Interpreted into diffs in phase, intensity, and frequency
Further used to determine location of source
Middle ear
Consists of:
1- eardrum (aka tympanic membrane)
2- ossicles (three tiny bones)
What are the three ossicles?
1- malleus (touches tympanic membrane; transmits movement to incus)
2- incus (transmits movements to stapes)
3- stapes (transmits movements to oval window and liquid of inner ear)
**hammer, anvil, stirrup
Function of ossicles
Connects the eardrum to a second membrane (the oval window of the inner ear)
Transfers sound patterns from one membrane to the other (minimizes reflection of energy, amplifies soft sounds, protects inner ear from very loud sounds)
Describe what happens when sound waves travel down the ear canal
1- hit the eardrum
2- eardrum vibrates (mimicking vibration patterns in the sound wave)
**vibration maximized when air pressure on both sides of eardrum is equal (middle ear=air-filled chamber)
How is pressure equalization achieved in the middle ear?
Normal circumstances: Eustachian tube creates passageway between middle ear and the mouth (and thus the outside world)
Abnormal circumstances (ex: tube blocked by infection): pressure builds up in middle ear and causes an earache
How can you “pop” your ears?
Swallowing/chewing gum activates muscles around Eustachian tube
Can induce exchange of air and release of pressure (aka ears popping)
Extreme pressure differences cause what?
Tympanic membrane to rupture
Three parts of the ear
Outer
Middle
Inner
How is energy transferred in ear?
Eardrum to malleus to incus to stapes to oval window (force increased at each step which amplifies the sound energy)
Describe the middle ear reflex
Process that can impede the transfer of energy in very loud sounds
Involuntary contraction of muscles attached to the ossicles (stapedius and tensor tympani) in response to any sound above 80 decibels
Muscle contraction = bones pulled away from membranes
Damps vibrations
Protects oval window from being overly displaced
Protection is only partial so damage is still possible
Smallest muscle in the body
Stapedius
What is the inner ear encased in?
Temporal bone
Aka thickest part of the skull
Two connected parts of inner ear
Vestibular system (for balance) Cochlea (for hearing)
Vestibular system of the inner ear
- three semicircular canals (loops orientated in diff planes at right angles to each other that sense motion in three dimensions)
- utricle + sacchule (sense horizontal and vertical acceleration)
- *both lined with tiny hairs (cilia) and filled with fluid I
How does the inner ear maintain balance, fix the gaze and coordinate body motion?
- inner ear organs filled with fluid and lined with tiny hairs called cilia
- cilia attached to nerve fibers
- head moves = motion of fluid makes hairs bend
- triggers nerves to fire
- brain interprets patterns of activation as movement and orientation of the body in space
Otoliths
Small crystals of calcium carbonate floating in the fluid in the utricle and saccule which further stimulate the cilia
Cochlea
Coiled tube like a snail shell
No bigger than a marble
Divided lengthwise into three parts (scalae):
1- scala vestibuli (on top)
2- scala tympani (on the bottom)
3- scala media (aka cochlear duct; in the middle)
End of cochlea adjacent to middle ear=basal end
Far end of cochlea=apex
Filled with lymphatic fluid
Helicotrema=at the apex of cochlea; connects scala vestibuli and scala tympani
The path of sound that leads to hearing
- sound vibrations pass through the eardrum
- pass ossicles
- end up at oval window
- oval window vibrates causing complex pressure waves to move thru lymphatic fluid in the cochlea
- waves move up scala vestibuli
- around helicotrema
- down scala tympani
- at basal end of scala tympani=membrane called round window
- round window expands and contracts as sound waves impact it (acting as a pressure release valve)
- pressure waves move thru cochlea
- cochlear duct becomes deformed
- deformation=hearing !!!
What are the two membranes separating the cochlear duct from the scala vestibuli and the scala tympani?
Top (from scala vestibuli): vestibular membrane
Bottom (from scala tympani): basilar membrane
What two parts are the basilar membrane touching?
1- connected to protrusion of the temporal bone, a bony shelf that supports the inner ear
2- on top of basilar membrane=tunnel-shaped set of structures known as ORGAN OF CORTI
What does the organ of Corti consist of?
A set of hair cells spread out along the cochlear duct
Hair cells connected to nerve cells
Fine hair cells (stereocilia) protrude from the hair cells
What covers the stereocilia?
Tectorial membrane
Described as gelatinous flap
What is the organ of Corti bathed in?
Bathed in lymphatic fluid that fills the cochlear duct
How is sound interpreted in the cochlea?
- pressure waves reverberate thru scalae
- basilar and tectorial membranes move
- stereocilia deforms
- connected nerves fire
- nerve signals carried thru auditory nerve to brain
- interpreted as sound
How do the stereocilia send their own very low amplitude signals?
They move in delayed response to (or sometimes in absence of) external stimulation
Can be heard as acoustic admissions by sensitive microphone placed in the ear
Sign of healthy auditory system
What part of the ear distinguishes different sounds, and how?
Depends on structure of BASILAR membrane
Not the same along its length
Basal end=thin and stiff; supported by bony shelf
Apex=bony shelf tapers off; basilar membrane is thicker and less stiff
Tapered shape creates fine-tuned spectral analysis of the incoming pressure wave
Oval window vibrates + sends pressure waves thru the scalae
Basilar membrane deforms bc waves
Place of greatest deformation depends on frequency
Thin end of basilar membrane=responds to high frequencies; thick end=low frequencies; middle=every frequency in between
How is complex sound responded to?
Different parts of basilar membrane will respond to the diff component frequencies
Amplitude of vibration of basilar membrane at a certain points depends on relative amplitude of frequency in signal (greater amplitude -> greater displacement -> stronger firing of nerves)
This organ of Corti creates complete spectral analysis (frequency + amplitude info encoded in message sent to brain)
Describe relationship between acoustic frequency and perceived pitch
Bc frequency response not evenly distributed along the basilar membrane, relationship between acoustic frequency and perceived pitch= non linear
**more than half basilar membrane devoted to most important frequencies for distinguishing speech sounds
What range is the cochlea devoted to?
200-3000 hz
Humans can discriminate sounds in this range better than higher or lower
**humans can’t hear above 20,000 hz but dogs bats and dolphins can
Conductive hearing loss
When sound is not being properly transferred from outer to middle to inner ear
Neurosensory hearing loss
Inner ear not properly responding to sounds it receives
How does congenital deafness (from birth) occur?
Part of the ear doesn’t develop normally
What are some ways that the ear can be damaged ?
- infections and tumours (inner/middle ear)
- some meds cause neural or hair cell damage as side effect
- exposure to high amplitude noise
- stereocilia damage from over stimulation
- aging (structures of ear stiffen over time and stereocilia damaged and lost)
How do hearing aids work?
Undo partial hearing loss by boosting amplitude of frequencies to which the ear has lost sensitivity
How do cochlear implants work ?
Bypass the ear completely
Directly stimulate auditory nerve cells in the way that the cochlea would if it were working
Detects level of sound energy at different frequencies and stimulate appropriate nerves accordingly
Tympanic membrane
- air right
- works like a microphone
- protects inner ear from high sounds pressure through partial oscillations
Is the tympanic cavity air tight?
No, because if it were, the variations in air pressure would pull/push on the tympanic membrane
The Eustachian tubes
- from middle ear to nasopharynx
- normally closed, loosely together
- can be opened by yawning/swallowing
- large air pressure differential between ends=air forced through tube (ex: airplane landing/taking off)
How is sound transmitted in the ear?
- the ossicles increase the pressure variations by 22
- as a result of surface area changes and leverage
- pressure variations in inner ear are 22x stronger than original pressure of sound waves
- amplification of 27 dB
What are the three parts of the cochlear tube?
Scala vestibuli
Scala tympani
Scala media
What does the cochlea do?
Transforms sound waves into neural impulses which pass through auditory nerve to brain
Two windows of the base of the cochlea
Oval window: where pressure waves reach cochlea (scala vestibuli)
Round window (scala tympani): releases sound waves back into tympanic cavity; adjusts pressure inside cochlea
Apex of the cochlea
Helicotrema !!!
Tip
Thinner and wider
Softer
Path of the scala vestibuli vs the scala tympani
Scala vestibuli: oval window to apex
Scala tympani: apex to round window
**both are filled with fluid
Basilar membrane
Separates scalas Where auditory nerve originates Oscillates Transmits pressure waves as transverse surface wave (but movement controlled by the brain) Contains the organ of Corti
Describe the way sound travels from the tympanic cavity, to the apex of the cochlea and back out into the tympanic cavity?
Through the oval window via the scala vestibuli, to the helicotrema, then back to the oval window via the scala tympani
What are the two types of info that the movement of the basilar membrane send to the brain?
Frequency
Amplitude
How does the organ of Corti create neural impulses
- linked to auditory nerve
- contains outer and inner hair cells
1- sound happens 2- moves outer hair cells 3- amplifies endolymph movement 4- moves stereocilia of inner hair cells 5- change in electrical impulse =neural impulse!
Outer hair cells
20,000 of them
Mechanical amplifier of quieter sounds
Touch both basilar and tectorial membranes
How do the outer hair cells work ?
1- sound causes basilar membrane to vibrate (causes shearing between basilar and tectorial membranes)
2- moves the stereocilia back and forth
3- movement of the stereocilia cause the cells to shorten then lengthen (electro motile response)
4- amplifies the movement of the endolymph
**also regulated by neural impulses from brain and responsible for oto-acoustic transmissions
Oto-acoustic transmissions
Outer hair cells are responsible for this
Def=an echo caused by the brain sending signals to outer hair cells
-causes basilar membrane to move
-what newborns are tested for in the hospital
Inner hair cells
3,500 of them
Covert mechanical movement of basilar membrane into neural impulses (transmit info to brain)
Don’t touch tectorial membrane (react to changes in endolymph speed caused by outer hair cells)
How is pitch interpreted?
Brain interprets pitch of sound based on location of cells sending impulses
- basilar membrane (base=thin and stiff, apex=thick and less stiff)
- hair cells: shorter and stiffer hairs at base=high frequencies, longer and more flexible hairs at apex=low frequencies
How the brain interpret loudness?
Based on number of hair cells activated
Displacement of basilar membrane
Does hearing = perception?
No, physical stimulus doesn’t equal auditory sensation
Non-linear relationship between frequency (acoustic property) and pitch (perceptual correlate)
Half of the basilar membrane dedicated to frequencies for speech (200-3000hz, were better at distinguishing these)
Sounds and their damage
Typical convo: 60 dB
Prolonged exposure causes hearing loss: 85 dB
Threshold for pain: 120 dB
Maximum MP3 player volume: 110 dB (hearing damage after just 1 hour per day)
