Auditory System I Flashcards
What are the three main subdivisions of the human ear?
The outer ear
the middle ear
the inner ear
What are the two functions of the outer ear?
Collection
Collect sounds
The shape of the pinna called in the localization of sound
What is is the function of the middle ear?
Amplification
Solves the “impedance mismatch” problem between the air (from the outer ear) and the fluid-filled spaces of the inner ears
Efficiently transfer acoustic energy from compression waves in air to fluid
True or False: Liquid is much less compressible so when soundwaves hit an air/liquid interface they become very much attenuated
Amplification (Middle ear)
True
Three bones of the middle ear take the vibration of the large _______________ and compress it into the small area of the ___________ allowing a relatively large wave to be set up in the fluid-filled inner ear.
Tympanic membrane
Oval window
Where can you find the sensory receptors of the auditory system and where sensory transduction occurs?
In the inner ear
Which ear is much simpler than the mammalian ear? Why?
Amphibian ear
- no external ear
- no middle ear –> because there is no impedance mismatch between the water they live in and the fluid-filled inner ear
True or False: Fish have specialized structures for hearing.
False: they have no specialized structures for hearing
Let’s look at the inner ear
What are the type of cells that transfer sound waves into a neuronal signal?
Hair cells
Where are hair cells located?
Located in the organ of Corti
that sits in the scala media on the basilar membrane
What are stereocilia?
They are mechanoreceptors that respond to the movement of their hairs.
They sit on top of the hair cells
When stereocilia are moved towards the shortest sterociliuluim the cell (depolarized/ hyperpolarizes)
When stereocilia are moved towards the tallest sterociliuluim the cell (depolarized/ hyperpolarizes)
Hyperpolarizes
Depolarized
What causes the change in membrane potential of hair cells, when the stereocilia move?
Non-specific cation channels located in the tips of the stereocilia
What are the protein that is on the tip of the stereocilia?
Tip Links –> Spring Link Proteins direct connected from tip of one stereocilium to the cation channel in the tip of neighboring stereocilia.
When the stereocilia moves toward the taller stereocilia, the tip links physically pull up on the channels causing them to (open/close) more.
Open
When the stereocilia move towards the shorter stereocilia, the tip links relax and the channels (open/close).
Close
What cation enter the hair cells that cause depolarization?
K+
due to very high concentration of K+ in the endolymph
What does this potential change do to V.G. Ca2+ channels in the basal portion of the cell membrane of the hair cell?
Open the channels
What do the influx of K+ and Ca2+ ions in the hair cell do to transmitter releases from hair cells?
Increase release ; Increase action potential firing in the 8th cranial nerve
True or False: Hair cells want to simplify the signal and one way to do is by adaptation.
True
Mechanisms of adaptation in the hair cells in the movement of tip links. They are attached by a ________ to actin filaments in the stereocilia.
Myosin Motor
True or False: The motor is constantly running up the actin filament to keep the tip links tight, such that at rest (when the stereocilia is not bent) about 15% of each cation channels are open.
True
When ____ enter the cell, as well as causing transmitter releases, it causes the myosin to slip (up/down) the actin filament, (strengthening/loosening) the tip links.
Ca2+
down
loosening
The myosin motor slipping down and the loosening of the tip links mean that the same movement of the stereocilia will open the channels and (more/less) transmitter is released –adapted.
Less
Encoding frequency
Hair cells at (different/similar) places along the _________ in the cochlea response to (similar/different) frequencies (pitches) of sound.
Different
Basilar membrane
different
What can you use to plot the different response of hair cells to different frequencies of sound?
Auditory tuning curves
True or False: Tuning curves are plotted showing the cell response level given by the frequency of the sound stimulus. (Auditory System)
False
Rather plots the threshold of sound intensity at which the cell responds to a given frequency of the sound stimulus.
What is “best frequency” or “characteristic frequency”?
The frequency to which an auditory cell at the lowest intensity response to the most.
What is the main cause of the frequency tuning of hair cells in mammals?
Different parts of the basilar membrane vibrate in response to different frequencies of sound.
What do the first two graphs respond in the basilar membrane?
Apical
The (apical/basal) end of the basilar membrane is thick and narrow, response to higher-frequency sounds.
Basal
The ____ the membrane moves, the more the hair cell stereocilia bend, and so the more hair cells _________.
Therefore the hair cells at the _______ end of the membrane depolarize in response to high frequencies sound while those at the ______ end depolarize in response to low-frequency sounds.
More
Depolarize
basal
apical
Which species’ hair cells can generate oscillating membrane potentials?
Lower vertebrates
What happens when the Ca2+ gated K+ channels open?
Recall, that there at the bottom of the hair cells in the perilymph region. (low [K+])
K+ moves out –> hair cells are hyperpolarized
When the Ca2+ gated K+ inactivate quickly, what happens when they close?
The cell is depolarized again if the sound is still present.
What is electrical tuning frequency?
The frequency at which the membrane potential oscillates when a hair cell is depolarized.
The frequency of the electrical oscillation matches the best frequency of the hair cells, so it ______ the response of the hair cells.
Amplifies
Outer hair cells (contracts/extends) when they are polarized.
Contract
Outer hair cells (extend/contracts) when they are hyperpolarized.
Extends
The contraction of the outer hair cells moves the basilar membrane ________ at their hair cells best frequency, ______ the motion of the membrane in response to that frequency of sound.
up and down
magnifying
Central auditory pathways
Information leaves the _______
Enter the brain via __________
________ synapse in several brainstem neclyi which send projection to the __________.
The _____ then sends connections to the auditory cortex.
Cochlea
8th cranial nerve
8th nerve fibers
thalamus
MGN
What information is encoded in the auditory system, as in all sensory systems?
Stimulus modality
Intensity
Duration
Location
Hair cells and CNS auditory neurons encode _______ differently.
Intensity
Hair cells are _________ to different intesnities of sound
graded response
CNS auditory neruons fire _____.
A.P
Since all of the responses oscillate at the frequency of sound stimulus –> A.P are fired in ________ and the frequency of the burst is related to the frequency of the ____________.
burst
sound stimulus
True or False: The firing rate can be used to signal stimulus intensity.
False
Firing-rate cannot be used to signal stimulus intensity.
Instead the auditory system encoded intensity by the __________________.
of neurons that are firing in response to a given stimulus.
True or False: Duration encoded by how long the hair cells membrane potential is oscillating or how long the auditory neuron is firing
True
What is tonotopy in the auditory system?
Different locations on cochlea
What do different location on the cochlea correspond to?
Different sound frequencies
What do profoundly deaf patients lack? What are you still functioning?
Lack hair cells but have functioning 8th cranical nerves
Cochlear implants work by having ___________ along the basilar membrane and stimulate the nerves at ___________.
20 stimulating electrodes
20 different locations
The input of the 20 stimulating electrodes are not as precise a input of a normal human ear ___________, but it allows most patients to understand normal conversations.
16,000 hair cells
True or False: The auditory cortex is similar to somatotopic in the somatosensory cortex and the visual cortex.
True
In order to increase the decibel, threshold, measurement of a sound, one would have to alter its wave ___________
amplitude
What feature of the cochlear prevents it from rupturing when the fluid column is set in motion?
The pressure is relieved by pushing out the round window at the other end of the cochlea.
What effect does fluid movement in the cochlear have on the basilar membrane?
It creates a traveling wave that moves along the basilar membrane
In the figure below, if neuron 3 fires in this array, which direction did the sound come from?
The sound came from straight ahead
