auditory Flashcards
humans are stuck within the ___ to ____ range
20 Hz-20 kHz
Middle ear cavity is ___-filled
Inner ear is ___-filled.
If sound waves were to impinge directly on the oval window, the membrane would barely move. Most of the sound would be reflected back because the fluid in the inner ear is denser than air and resists being moved much more than air does.
Consequently, in order to drive the movement of the oval window and vibrate the fluid, greater ___ is needed.
Middle ear cavity is air-filled
Inner ear is fluid-filled.
If sound waves were to impinge directly on the oval window, the membrane would barely move. Most of the sound would be reflected back because the fluid in the inner ear is denser than air and resists being moved much more than air does.
Consequently, in order to drive the movement of the oval window and vibrate the fluid, greater pressure is needed.
conductive hearing loss
Diminished sense of hearing due to the reduced ability of sounds to be mechanically transmitted to the inner ear. Common causes include occlusion of the ear canal, perforation of the tympanic membrane, and arthritic degeneration of the middle ear ossicles. Contrast with sensorineural hearing loss.
endolymph
-what is found there?
The potassium-rich fluid filling both the cochlear duct and the membranous labyrinth; bathes the apical end of the hair cells.
fluid of the labyrinth and the cochlear duct
what is sound? ***
• In physical terms:
• In casual terms:
- In physical terms: pressure waves generated by vibrating air molecules
- In casual terms: sounds refers to an auditory percept
• Two physical components of sound
- Displacement component- movement of molecules
- Pressure component- More about the density of molecules
• Sound is created by pressure waves in air. These waves are often induced by vibrating membranes such as vocal cords.
***What part of sound can we hear?
• what component of sound are humans sensitive to?
-between what Hz?
• Human ears are sensitive only to the pressure component, and only between 20 Hz and 20 kHz alternating compression and rarefaction (reduction in density)
Two characteristics we attend to most:
frequency and intensity
Humans cannot actually detect the movement of sound molecules but are sensitive to the pressure compnent of sound between 20 Hz and 20 kHz alternating compression and rarefaction
define rarefaction and compression
Compression- get more dense
• Rarefaction- get less dense
frequnecy def
A. The spacing between waves or period. This can also be thought of in terms of how many wave cycles pass by in one second- that is, the sound’s frequency in Hz=cycles/second
intensity def (measured in..)
The intensity of amplitude of the sound measured in decibels.
Tasks of the auditory system
**
Tasks of the auditory system
- Resolve intensity (loudness) and frequency (pitch, timbre) components of sound stimuli
- Encode temporal features
- Localize sound sources in space
compression
- air molecules gets more dense
- Peak
do animal vocalizations, speech, and music or environmental sounds such as wind contain highly periodic elements?
Note that animal vocalizations, speech, and music can contain highly periodic (tonal and harmonic) elements, whereas environmental sounds such as wind lack such periodic structure. (Courtesy of Timothy Warren.)
audible spectrum
-does it differ among species?
Species-specific
May have to shift want saying depending species
This, in turn, has an effect on the types of vocalizations each animal makes
Stick to ones within the realms of perception
Humans try to keep speaking within the spectrum
Same with the other species
Mice are always chatting – we just cant hear it (goes outside our range of hearing)
We are blocked within our rhelm of hearing
***How does the outer ear contribute to hearing?
- The outer ear and canal guide, amplify, and filter sound.
- Collects the sound energy and concentrates it on the TYMPANIC MEMBRANE (ear drum)
- The tympanic membrane and ossicles transmit the vibrations to the cochlea
- Especially effective at amplifying sounds in 2-5kHz range… super important for speech perception
- -Helps determine elevation of sound
• All sound is still air-based at this point
tympanic membrane
eardrum
-this is where the outer ear collects the sound energy and concentrates it
what air sound runs into
for what range is the outer ear effective at amplifying?
this helps to determine?
- Especially effective at amplifying sounds in 2-5kHz range… super important for speech perception
- -Helps determine elevation of sound
How does the middle ear contribute to hearing? ***
The vibrations from the eardrum set the ossicles into motion. The ossicles are actually tiny bones — the smallest in the human body. The three bones are named after their shapes: the malleus (hammer), incus (anvil) and stapes (stirrup). The ossicles further amplify the sound. The ossicles connect the tympanic membrane to the oval window
• At this point, we need to start converting sound in air to sound in liquid (Remember- sound consists of pressure waves). The tympanic membrane and auditory ossicles are a mechanism for transferring sound energy from the air medium to the liquid medium of the cochlea
• Air: low impedance; Liquid: high impedance
Each sound pressure wave moves the tympanic membrane back and forth, ultimately moving the oval window back and forth.
• Since liquid in the cochlea is incompressible, movements of the oval window are compensated for by movements of the round window.
• Oval window-
membrane where the bones of the middle ear meet the inner ear
• Ossicles
- little bones (malleus, incus, and stapes) that connect the tympanic membrane to the oval window. Move in response to sound/movement of tympanic membrane. Their movement causes movement of the oval window
• Oval window-
• Oval window- membrane where the bones of the middle ear meet the inner ear
• Stapedius
- smallest muscle in body; helps stabilize the stapes
• Innervated by cranial nerve VII (facial nerve)
Tensor tympani
Tensor tympani- connected to the malleus
• Innervated by cranial nerve V (trigeminal)
why is chewing not that loud
- Together, the muscles help dampen loud sounds (thunder, chewing) by counteracting the movement of the ossicles to the sound
- Reducing the amount of sound going from one side…
- This is why chewing is not that loud
- Super loud noises: dampening it down
mechanism for transferring sound energy from the air medium to the liquid medium of the cochlea
The tympanic membrane and auditory ossicles are a mechanism for transferring sound energy from the air medium to the liquid medium of the cochlea
• Air: low impedance; Liquid: high impedance
the cochlea tansduces action potentials in the?
sound is transduced into depolarizations and then action potentials in the vestibular-cochlear nerve (cranial nerve 8) **
the cochlea can only perceive sound, not amplify it T/F
FALSE - can also amplify it
• Vibrations enter the cochlea via the ____ and exit via the ____
• Vibrations enter the cochlea via the round window and exit via the round window.
• Chambers of the chochlea (probs label these too)
•
- the scala tympani: The lowermost of the three chambers. It too has a basal aperture, the round window, which is closed by an elastic membrane.
- The scala vestibuli: forms the upper chamber
- The scala media (cochlear duct): separates the other two chambers along most of their length.
what type of coding is found in the cochlea? explain it
tonotopic map- a location code- formed on the cochlea. due to the basilar membrane
higher frequencies cause movement in the _____ of the cochlea, and deeper frequencies work at the _____.
higher frequencies cause movement in the base of the cochlea, and deeper frequencies work at the apex.
Reissner’s membrane
divides the scala vestibulli and the scala media
How is vestibular information collected? What types of movements are detected? Where does that information go? ***
- Utricle and Saccule- respond to translational movements (linear motion) of the head and static head position in relation to gravity
- Semicircular canals- respond to rotations of the head
• information gets relayed to the cerebellum, thalamus, and the cortex
What types of movements are detected by the vestibular information?
- translational movements (linear motion) of the head and static head position in relation to gravity : Uticle and Saccule
- rotations of the head: Semicircular canals
Air vs liquid in regards to impedance
Air: low impedance; Liquid: high impedance
impedance is = resistance i think
Labyrinth is composed of
Composed of two otolith organs- the utricle and saccule- and three semicircular canals
-vestibular information
Semicircular canals
the semicircular canal has hair cells in its ampullae (swellings at base)
- each canal has the hair cells oriented in one direction, giving a pretty good representation of X, Y, and Z axes
*rotations of the head
THE SEMICIRCULAR CANALS: HORIZONTAL, POSTERIOR, AND ANTERIOR.
These three semicircular canals lie perpendicular to one another and detect rotational acceleration
otolith organs*
collective term used to refer to the utricle and the saccule, two components of the vestibular system that are designed to detect gravitational forces and linear acceleration of the head.
do pressure waves usually have fixed spacing? why or why not?
• Because the membranes usually vibrate in a regular manner, the pressure waves have a fixed spacing.
the first membrane sound hits in the outer ear is
the tympanic membrane
cochlear duct
The scala media (cochlear duct): separates the other two chambers along most of their length.
order of the three bones
malleus, incus, stapes
the stapes strikes the oval window.
The Basilar membrane
The Basilar membrane separates the cochlear and tympanic ducts.
-on which the cohlear hair cells are located
The basilar membrane is thinnest at its ___ and widest at its ___.
The basilar membrane is thinnest at its base and widest at its apex.
Auditory cortex- where is it, how is it organized, what is it doing ***
- In the temporal lobe
- Conscious perception of sound
- Recognition of speech and music
- Not as well understood as other sensory regions of the cortex
- We do know that core divisions of the auditory cortex get a tonotopic map based off of the topographical map of the cochlea
The primary auditory cortex is a map of the _____
The primary auditory cortex is a map of the contralateral cochlea
Where does the thalamus get its information?
from the inferior colliculus
How is the primary auditory cortex organized?
The primary auditory cortex is tonotopically organised, meaning that the cells within the cortex, will receive inputs from cells in the inner ear that respond to specific frequencies.
The medial geniculate nucleus=
The medial geniculate nucleus - This is the nucleus of the thalamus that acts as the relay point between the inferior colliculus and the auditory cortex. The lateral geniculate nucleus (involved in the visual pathway) lies adjacent to it
How is the medial geniculate nucleus organized?
Believed that everything is still tonotopically mapped here
how is sound localized?
horizontal: uses the interaural time difference and intensity difference to judge where the sound is coming from; time by medial superior olive, intensity by lateral superior olive
vertical: reflections off the pinna with processing by the cochlear nucleus and superior olivary nucleus
What is the inferior colliculus doing? Who brings it information and where does it send axons?
*****
- Receives all of the good auditory info from the superior olive and nuclei of the lateral lemniscus
- Appears to be the site of our auditory space map
- Neurons in this area respond best to sound originating in specific regions of space in all planes
- Also can process sounds with complex temporal patterns
- Some cells respond to sounds of specific durations.. Some to specific temporal sequences
* Important for things like predator noises and speech
- Some cells respond to sounds of specific durations.. Some to specific temporal sequences
*stronger stimulus to left ear =>
- stronger stimulus to left ear excites left LSO and inhibits the right LSO (via the MNTB interneuron)
- the right LSO is inhibited via the MNTB interneuron
–>on the left side: excitation from left side is greater than inhibition from right side, resulting in net excitation to higher centers on left side
AND
–>on the right side: inhibition from left side is greater than excitation from right, resulting in net inhibition on right and no signal to higher centers
sends info to the inferior colliculus **
• MSO, LSO, Nuclei of the Lateral Lemniscus –> inferior colliculus
• Cochlea transmits sound information to ____
• Cochlea transmits sound information to the lateral superior olive (LSO) and medial nucleus of the trapezoid body (MNTB)
what structures make up the inner ear?
what structures make up the inner ear?
cochlea and vestibular labyrinth
what occurs with the fluid in the cochlea?
what occurs with the fluid in the cochlea?
the fluid is moved by the sound waves – propagate through the fluid
what cranial nerve is formed by the auditory and vestibular nerves?
what cranial nerve is formed by the auditory and vestibular nerves?
cranial nerve 8
what cranial nerve is formed by the auditory and vestibular nerves?
cranial nerve 8= vestibulo-cochlear nerve
what is the purpose of the ossicles?
what is the purpose of the ossicles?
increase pressure and force with which the stapes contacts the cochlea at the oval window – given amount of force over a smaller area
what is the role of the tensor tympani and the stapedius?
when these contract and pull together, it keeps the ossicles from moving too much –protects from loud sounds
what is the structure of the cochlea?
wound up like a snail; has the basilar membrane, where the hair cells sit in it
sound waves in the cochlea travel from base to apex or apex to base?
base to apex I think
ratio of inner hair cells to outer hair cells
1:3
ratio of outer hair cells to inner hair cells
3:1
where does the auditory nerve branch from?
where does the auditory nerve branch from?
from the cochlea
how are different frequencies processed in the cochlea?
lower frequencies processed more toward the apex; higher frequencies processed earlier, near the base – this is because high frequencies vibrate a lot at base and then dissipate, which the apex, tuned for low frequencies, is more flexible than the base
what is tonotopic mapping?
the response of the basilar membrane establishes a place code in which different locations on the membrane are maximally deformed by different frequencies
- tonotopic mapping and neural coding of pitch
what is the organ of corti?
what is the organ of corti?
in the middle scala of the ear, the actual hearing apparatus; located within the cochlea
outer hair cells
receive input from axons that arise from cells in the brain (superior olivary complex).
Help with amplification of low-level sounds
Help modify motion of basilar membrane
inner hair cells
IHCs: sensory receptors; 95% of the fibers of the auditorynerve that project to the brain arise from this subpopulation.
what type of transduction is hearing based on?
The ability to hear is essentially dependent on mechanoelectrical transduction
Mechanotransduction (mechano + transduction) is any of various mechanisms by which cells convert mechanical stimulus into electrochemical activity
olivocochlear bundle
supplies efferent input to the OHCs
stimulation can broaden CNVIIInerve tuning curves
what fluid is within the scala media, and what is its composition (of ions)?
what fluid is within the scala media, and what is its composition (of ions)?
endolymph – high in potassium and low in sodium
the basilar membrane at low sound intensities
*nonlinear vibration
It seems likely that the OHCs sharpen the frequency-resolving power of the cochlea by actively contracting and relaxing, thus changing the stiffness of the tectorial membrane at particular locations. ==> nonlinear vibration
what fluid is within the scala media, and what is its composition (of ions)?
endolymph – high in potassium and low in sodium
what fluid is within the scala vestibuli and scala media, and what is its composition?
perilymph; high in sodium and low in potassium
Inner Hair Cells and Transduction
Stereocilia bend together
Cation-selective hcMET channels open near the tips
K+ flows into the hair cell
Hair cell depolarizes
Opening of voltage-gated calcium channels calcium entry
Release neurotransmitter (glutamate) onto the nerve endings of the auditory nerve
Much like taste cells, hair cells are NOT neurons
t/f taste cells are neurons
FASLE
Much like taste cells, hair cells are NOT neurons
t/f hair cells are NOT neurons
TRUE
Much like taste cells, hair cells are NOT neurons
what is created by the endolymph in the scala media?
endocochlear potential due to being more positive that the perilymph
what is created by the endolymph in the scala media?
endocochlear potential due to being more positive that the perilymph
what is created by the endolymph in the scala media?
what is created by the endolymph in the scala media?
endocochlear potential due to being more positive that the perilymph
what leads to depolarization of the hair cells?
influx of potassium; fluxes into the hair cells and the influx of a positive ion depolarizes them
what is the stria vascularis?
located on the wall of the cochlea within the scala media, its cells maintain the endocochlear potential through active transport
The endolymph
- the fluid of the inner ear
- is high in K+ and low in Na+
Has to do with the ion-pumping cells in the stria vascularis
phase-locked
Inner hair cells only depolarize during certain phases of the sound wave (due to cilia movement) afferent nerve fibers are therefore phase-locked to the positive phases of sound… or at least low-frequency sounds
•Phase
•Phase - specifies the location or timing of a point within a wave cycle of a repetitive waveform
4 features of sound waves and why they are relevant **
5.3) 4 features of sound waves and why they are relevant
•Waveform- amplitude plotted against time or distance
•Phase - specifies the location or timing of a point within a wave cycle of a repetitive waveform
•Amplitude - usually expressed in decibels
“Loudness”
•Frequency - expressed in cycles per second (Hertz)
“Pitch”
Encoding sound intensity and frequency
Phase locking
(different group of neurons firing different phase of some cycle:Some only fire on trough, only on peak, some always fire etc) *we give information of frequency of sound
consistent firing of a cell at the same phase of a sound wave
- Low frequencies (up to 4 hz): phase locking on every cycle of some fraction of cycles
- High Frequencies (More than 5hz): Not fixed
Encoding sound intensity and frequency
Phase locking In brain stem neurons:
- Low frequncies: Phase locking is used
- intermediate frequencies: Both phase locking and tonotopy are useful
- High Frequencies: Tonotopy is used to indicate sound frequency
how do the membranes with the organ of Corti move?
tectorial membrane remains stable while the basilar membrane moves up and down, allows for movement of the stereocilia within the hair cells
what is the role of the inner hair cells? the outer hair cells?
what is the role of the inner hair cells? the outer hair cells?
inner hair cells transduce most of the sounds; outer hair cells are thought to play a role in amplifying the sounds
what is the role of the direction of the shearing force?
what is the role of the direction of the shearing force?
determines polarization; toward the kinocilia – depolarization; away from the kinocilia – hyperpolarization
why does movement of the stereocilia allow for an ion influx?
activates mechanosensitive channels that allow for influx of potassium
terminus of the primary auditory pathway
auditory area 1 (A1)
what occurs in the hair cells following depolarization?
activates voltage gated calcium channels, causing release of a neurotransmitter and activation of the auditory afferent
(Release neurotransmitter (glutamate) onto the nerve endings of the auditory nerve)
what is observed with the tonotopic mapping on the cochlea as we go into the nervous system?
what is observed with the tonotopic mapping on the cochlea as we go into the nervous system?
this arrangement remains as we go into the nervous system and into the auditory nerves; into the cochlear nucleus of the brainstem – cell bodies of the auditory nerve are situated in what is called the spiral ganglion
localizing sound : higher frequency **
Higher frequencies
•For higher frequencies, intensity differences between the two ears must be used.
•At these frequencies, the sound wavelength is so short that the waves cannot bend around the head, so the head creates a sound shadow that enhances the effect.
what is the pathway for sound?
what is the pathway for sound?
comes in through the auditory nerve, synapses in the cochlear nucleus in the medulla – a couple different cochlear nuclei: dorsal, ventral; dorsal info projects to the inferior colliculus, and synapses in the medial geniculate nucleus of the thalamus – has an unusual secondary synapse in the brainstem; the ventral nuclei project to the superior olive in the brainstem, which projects bilaterally, with the axons ascending in the lateral lemniscus to the inferior colliculus
-Axon from the right and left cochlear nuclei go to the
medial superior olive (MSO)
medial superior olive (MSO) *
- where differences between the two ears are measured
- -Axon from the right and left cochlear nuclei go to the MSO
-Coincidence detector cells
the lowest threshold of a tuning curve
characteristic frequency
Coincidence detector cells:
Coincidence detector cells: respond when excitatory inputs arrive at the same time
Neurons sensitive to different time delays
- A neuron that detects simultaneous events, as in sound localization
- i think part of the MSO
Unilateral hearing loss **
With single-sided deafness, you lose the ability to have spatial hearing (localization in the horizontal plane)
- Cannot rely on time or intensity differences so the inferior colliculus is not receiving the infroaiton – cannot map the cels well – having a hard time processing where it is coming from
- Also have the addition of the head-shadow effect, which is where the non-functional ear is in the acoustic shadow of the good ear on the opposite side of the head.
- Def of acoustic shadow:
- What ends up happening is a cumulative effect.
- Presents difficulty with speech intelligibility in the presence of background noise, and it is oftentimes the most prevalent when the speech target is presented at the ‘dead’ ear and the signal has to cross over the head and be heard by the only hearing ear on the opposite side
head-shadow effect
a result of unilateral hearing loss
-the non-functional ear is in the acoustic shadow of the good ear on the opposite side of the head.
hair cells transduce …
mechanical displacement into neural impulses
can hair cells regenerate?
Exposure to high intensity sounds can break the tips off. The cilia of human hair cells do NOT regenerate –> irreversible damage
The semicircular ducts are continuous with the
a. Utricle, saccule, and cochlear duct
b. Organ of Corti
c. Cribiform plate
d. Vestibulocochlear Nerve fibers
e. Stapes, Incus, and Malleus
Utricle, saccule, and cochlear duct
The endolymph of the scala media resembles which body fluid in its composition?
a. Interstitial fluid
b. Plasma
c. Cerebrospinal fluid
d. Lachrymal gland secretions
e. Intracellular fluid
The endolymph of the scala media resembles which body fluid in its composition?
Intracellular fluid
our ear is air filled vs middle ear is air filled
outer ear is air filled vs middle ear is air filled
both are air filled, inner ear = liquid
Nuclei of the Lateral Lemniscus
Respond to sound arriving at one ear only (monaural)
unilateral hearing loss
you lose the ability to have spatial hearing (localization in the horizontal plane) + Presents difficulty with speech intelligibility in the presence of background noise, a
