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108 Cards in this Set

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What is the function of the superior olivary nucleus in regards to hearing?
localization of sound
What is the function of the inferior colliculus in regards to sound?
localization of sound
What is the main thalamic relay point?
medial geniculate
What is the auditory cortex called?
Heschl's gyrus
Sound is a ________ wave that involves ________ increases and decreases.
sinusoidal
pressure
What is compression?
increase in pressure
What is rarefaction?
decrease in pressure
Is air an elastic or inelastic medium?
elastic
The molecules of air cause a __________ force on the eardrum.
mechanical
What is the normal hearing frequency range for humans?
20 Hz - 20 kHz
T/F: Humans can hear over a wide range of amplitudes.
True
Sound is measured in ______
decibels (dB)
L =
20*log10 (Pmeasured/Preference)
T/F: Humans are equally sensitive across frequencies.
False
Around what frequency do humans have the most sensitivity in hearing?
1 kHz
Damage occurs at or above ____ dB with persistent noise.
120
What is the central auditory pathway?
cochlea --> cochlear nerve --> cochlear nucleus -->
a) some fibers cross in traapezoidal body and go through superior olives --> inferior colliculus
b)some fibers don't go throug trapezoid body but go straight to inferior colliculus
IC --> medial geniculate --> cortex
Is hearing a unilateral or bilateral system? why?
bilateral; as soon as fibers leave cochlear nucleus some of them cross to the other side
What are the 3 fxns of the ear?
1. sound collection
2. transmission and amplification
3. mechanical to electrical conduction
What is the function of the outer ear?
collection of sound and focusing sound on the eardrum
What is the function of the middle ear?
transmission of sound from eardrum to oval window
What is the middle ear important for?
amplification
What fills the middle ear?
air
What is the function of the cochlea?
convert mechanical energy to electrical signal
What fills the chambers of the middle ear?
perilymph
What fills the scala media?
endolymph
What happens as sound travels through the middle/inner ear?
vibrations cause oscillation of small bones --> pressure waves sent down perilymp filled chambers --> pressure released through membrane of round window
What is the main transduction organ?
organ of corti
Where does the organ of corti sit? What semi encapsulates it?
on the basilar membrane
tectorial membrane
Where are the hair cells?
in the region of the organ of corti
What is the structure of the basilar membrane important for?
frequency encoding (splits info info into component frequencies)
Describe the basilar membrane structure.
Near oval window it is narrower and less flexible
Near apex of cochlea it is wider and more flexible
What kind of frequencies does the narrow, unflexible portion of the basilar membrane respond to/detect?
high frequencies
What kind of frequencies does the wide, flexible portion of the basilar membrane respond to/detect?
low fequencies
The frequency a cell transmits depends primarily on its __________.
location on the basilar membrane
What causes fluid within the ear to move?
pressure differences
What are traveling waves? What records these waves?
pressure differences causes fluid to move;
basilar membrane records waves
Are waves uniform across basilar membrane?
no
Basilar membrane oscillates differently for different _________.
frequencies
Where are basilar membrane oscilations at low frequency?
low- near apex where membrane is widest
Does a wave have the same amplitude as it moves across the entire membrane with time?
no, waves quickly reduce in amplitude after their highest point so they aren't exciting other parts of the membrane
From what is the endolymph derived?
stria vascularis
What is found in high concentration in the endolymph? Is this typical of extracellular media?
potassium; no
What is the function of outer hair cells?
modulation of signal
What is the function of inner hair cells?
collecting auditory information
There are a greater number of ____ hair cells.
outer
What is contained in the chamber below the basilar membrane? Does it have a high/low/normal K concentration?
perilymph; normal K concentration
What are the cilia of a hair cell in contact with?
tectorial membrane
How does K inter a hair cell? Why does K enter cell?
through stereocilia; there is a huge driving force for K to enter cell
What kind of membrane signal can be generated when K enters hair cell?
a 20-30 mV signal
What is the potential of the endolymph compared to the perilymph?
endo is 80mV more positive than perilymph
What is the membrane potential across the basilar membrane?
-45 mV (normal for an excitable cell) (-45mV inside cell and 0 mV outside cell)
What happens in the hair cell after the initial signal?
depolarization and activation of voltage gated Calcium channels --> depolarization and vesicle release
What kind of channels does initial depolarization activate?
Ca and K
What happens when K channels are activated?
allows for extrusion of K into perilymph and dissipatation of signal
Explain what happens in hair cell depolarization.
basicallyl K moves from one side of the cell to the other and creates a depolarization which activates Ca channels
What is the largest cilia in a hair cell?
kinocilium
Molecular links connect (individual cilia/isolated structures).
individual cilia
K channels are ____________-
mechanosensitive
What causes K channels to open?
basilar membrane moves --> shearing between tips of cilia and tectorial membrane --> tension on tip link
What determines whether K channels will open or close?
the way the tectorial membrane bends
What happens if the K channels close?
hyperpolarization
What is the proposed mechanism for hearing involving hair cells?
-strong attachment between cilia and tectorial membrane
-as pressure changes in perilymph the membrane moves and there is shearing between tect. membrane and cilia
The auditory canal is a ____________ channel.
mechanosensitive
What is the encoding frequency largely dependent upon?
the properties of the basilar membrane itself
What is the primary cause for deafness?
loss or damage to hair cells
What does a cochlear implant do?
allows a person to bypass the hair cells by directly stimulating afferent nerve fibers
What exactly is stimulated by a cochlear implant?
the current produced by the stimulating electrodes must be sufficient to cause action potentials in the afferent fibers directly
Why can't a cochlear implant stimulate the basilar membrane?
even if it was able to vibrate the membrane - the hair cells are dead and so there would be no signaling
Where is a cochlear implant placed?
winded into the cochlea
How does a cochlear implant work?
-a microphone collects sound
-a processing unit splits it into various frequencies and sends them to wires which cause stimulation of the appropriate part of the basilar membrane
T/F: With a cochlear implant you need to hit all frequencies in order to hear sound properly.
F: You only need to hit certain frequencies
What substance is hair cell synapse dependent upon?
Ca++
At a hair cell synapse, vesicles are arranged around a _______, _______ dense body and ultimately fuse and release __________ onto post-synaptic side.
circular, electron dense;
glutamate
T/F: Vesicle to post-synaptic plasma membrane fusion is the only fusion at a hair cell synapse.
F: there may be fusion of vesicles to each other
What are the four sets of nerve fibers in the auditory system and what do they innervate?
1.2 olivocochlear efferents: brain --> inner and outer hair cells
2.primary afferents: inner hair cells
3.secondary afferents: outer hair cells
Which type of hair cells are more sensitive and specific?
inner hair cells
What is the difference between inner and outer hair cells conveyance of sound to CNS?
Inner: convergence of afferent fibers, each hair cell has 10 afferent outputs to CNS [1:10 ratio]
Outer: lots of divergence of afferent fibers [10:1 ratio]
How many inner hair cells are there? outer hair cells?
Inner: 3,500
Outer: 14,000
What can depolarize outer hair cells?
K+ or a patch electrode
What happens when outer hair cells depolarized?
the cells change shape by contracting or expanding
How does cochlear fluid affect the sensitivity of outer hair cells?
it dampens movement of the basilar membrane
Outer hair cells have ______ efferent innervation and ______ afferent innervation
extensive; limited
What encodes loudness/intensity of sound?
firing frequency of action potentials in nerve
As sound increases the number of action potentials...
increases.
What is the saturation point for intensity?
around 500Hz
T/F: Perception of sound might not change much over higher range.
True
What 2 things does encoding frequency depend on?
1. location of the cell on the basilar membrane
2. phase locking
What is phase locking?
If a sinusoidal wave brings information into the membrane and excites hair cells, the output gets locked to the phase of the waves.
At a ____ frequency, information is lost but the position on the _________ is still present.
high;
basilar membrane
What modulates signals from inner hair cells? How?
outer hair cells; when stimulated directly by efferents, they make inner hair cells less sensitive
What can get rid of background noise? How?
outer hair cells; background noise masks a tone but when the sensitivity is decreased (by outer hair cells) background noise is not detected as well
In what 2 ways are outer hair cells important?
1. increasing movement of basilar membrane (amplification)
2. changing the sensitivity of the inner hair cells and their afferent connections to the CNS
Describe the ascending pathway of the auditory axis.
CN VIII (spiral ganglion)
Cochlear nucleus
Superior Olivary nucleus
Lateral lemniscus
Inferior Colliculus
Medial geniculate body
Auditory cortex (transverse gyrus of temporal lobe)
Describe the output of the cochlear nucleus.
Some fibers cross in the trapezoid body and go to the superior olivary nucleus
Other fibers don't cross and go to the lateral lemniscus
How do we know which direction the sound comes from?
interaural timing differences and intensity differences
Explain interaural timing differences
When a sound comes in it is usually lateralized and hits one ear before the other which results in a timing difference between the two signals. The inner hair cells will be excited but one side will be delayed with respect to the other.
With respect to sound localization, what variables change and which stay the same?
change: frequency and wavelength
stay the same: distance between ears and speed of sound
The time difference in sound is largely dependent upon ___________.
angle to midline
Cells in the medial superior olive respond best with __________ input. They are innervated __________ and ___________.
Bilateral;
ipsilaterally and contralaterally (with slight delay in contralat.)
Explain the mechanism of intensity differences in determinig sound localization.
cells in the lateral superior olive respond better when a signal is less intense from one ear than from the other ear, a cell can respond strongly when stimulated by the ipsilateral side but not from the contralateral side
What happens in the cells of the inferior colliculus?
not much is known about processing here; a lot of the cells are sensitive to differences in aural delay and in intensity so thought to be involved in localization
What is the main relay station in the thalamus to get information to the cortex?
medial geniculate
What are the cells in the medial geniculate sensitive to?
-some are just sensitive to auditory information
-others are multimodal-sensitive to vision and somatosensation
Where is the primary auditory cortex?
temporal lobe (Heschl's gyrus)
How are cells in the auditory cortex arranged?
tontypically according to frequency
In the auditory cortex within areas of high and low frequency, cells are sensitive to both ____ and _____ of sound.
intensity and location
The primary auditory cortex is near what other important structures?
1.Broca's area of language processing and speech formation
2. Wernicke's area: speech comprehension