Auditory System I Flashcards by Benjamin Ayala

What are the three main subdivisions of the human ear?

The outer ear

the middle ear

the inner ear

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What are the two functions of the outer ear?

Collection

Collect sounds

The shape of the pinna called in the localization of sound

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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

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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

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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

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Where can you find the sensory receptors of the auditory system and where sensory transduction occurs?

In the inner ear

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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

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True or False: Fish have specialized structures for hearing.

False: they have no specialized structures for hearing

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Let’s look at the inner ear

What are the type of cells that transfer sound waves into a neuronal signal?

Hair cells

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Where are hair cells located?

Located in the organ of Corti

that sits in the scala media on the basilar membrane

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What are stereocilia?

They are mechanoreceptors that respond to the movement of their hairs.

They sit on top of the hair cells

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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

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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

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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.

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When the stereocilia moves toward the taller stereocilia, the tip links physically pull up on the channels causing them to (open/close) more.

Open

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When the stereocilia move towards the shorter stereocilia, the tip links relax and the channels (open/close).

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What cation enter the hair cells that cause depolarization?

K⁺

due to very high concentration of K+ in the endolymph

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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

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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

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True or False: Hair cells want to simplify the signal and one way to do is by adaptation.

True

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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

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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

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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

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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