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Neuro > Auditory > Flashcards

Auditory Flashcards

1
Q

What is sound?

A

Sound comes down to being a result of vibration out in the world.
Ex: Tuning fork –> vibrate at a specific frequency, pushing on molecules and making them move back and forth.

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2
Q

What will happen when the tuning fork is moving in one direction?

A

It will compress air molecules, and if it moves in another direction it will become less dense.

At the frequency of vibration you will get a repeated cycle of high and low pressure

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3
Q

Cycle length (wavelength)

A

Depends on the sound source and where it is.
Ex: if a predator steps on something and you hear, you may be able to run away from it.

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4
Q

What information is contained in sound?

A
  • Frequency (sounds consist of a mix of frequencies)

-Timing (how long does it take to get to you and when does it arrive at your two ears –> will help tell where it’s coming from and how far away it is.

-Loudness intensity, amplitude: how loud the sound is –> sound wave –> higher amplitude if you have a bigger sound.

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5
Q

3 levels of amplification:

A

Sound has to get into the head and will go through
-external ear –> focus sound and filter frequency

-middle ear –> Take the sound that is traveling in the air and convert it into a sound that can be detected in the fluid in the middle ear

-cochlea –> inner ear –> extracting information and transducing mechanical sound into electrical activity

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6
Q

Role of Outer ear:

A

Amplifies sound in frequency range of human speech (3 kHz)
Filters sound, depending on elevation

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7
Q

What happens when a person if a person is looking straight ahead at 0 degrees?

A

The best frequency will be around 5kHz

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8
Q

What happens when a person if a person is looking straight ahead at 0 degrees?

A

The best frequency will be around 5kHz

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9
Q

What happens when the sound is above the head?

A

The outer ear shifts the frequency to make it sound like a higher frequency

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10
Q

What happens when sound is below you?

A

Your outer ear shifts the frequency to sound lower

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11
Q

Middle ear:

A

Provides impedance matching bc sound getting into our heads has a built-in mismatch.

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12
Q

What medium does sound travel in?

A

It is traveling air

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13
Q

What’s inside our heads?

A

Fluid

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14
Q

Every animal that listens to sound from a distance uses an eardrum of some source. This is impedance matching

A

We collect sound using eardrum, and transmit to the oval window through the ossicle (middle ear bone –> malleus, incus, stapes)

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15
Q

The inner ear connected to the oval window will be doing the transduction: What is the middle ear doing?

A

The eardrum is collecting sound and the middle inner ear bones are focusing the sound on the oval window of your inner ear. If you don’t do this sound will bounce right off

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16
Q

The cochlea (inner ear)

A

Oval part –> cochlea –> transducing mechanical energy into electrical signals. Cochlea is a fluid-filled tube that has a membrane running down the middle of it.

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17
Q

3 steps of analysis:

A
  • The membrane in the cochlea is going to have a traveling wave and where the membrane vibrates most with the highest amplitude –> tell what frequency is. Wave will travel down the membrane.
  • Hair cells detect traveling wave motion (have cilia –> transduce mechanical stimuli into electrical signals) when those cilia’s are deflected by the basal membrane that causes the depolarization of the hair cell and the activation of sensory neurons.
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18
Q

What is cochlea?

A

It is a fluid-filled canal with a flexible partition –> a tube that is divided by a flexible membrane.
In the middle of the tube are a basilar membrane and another tectorial membrane both important for transduction.

Those membranes divide the fluid inside the tube into two different departments –> scale tympani and scale of the vestibule

Surrounding the transduction apparatus is the scale of media.

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19
Q

The stapes (final bone) push on the oval window and will vibrate at the same frequency as whatever sound is traveling through the air.

A

This creates a traveling wave in a scale of vestibuli and travels along the basilar membrane.

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20
Q

Cochlea unrolled

A

Big tube –> membrane dividing upper (scala vestibuli) and lower areas (scale of tympani). The stapes is pushing on the oval window providing pressure waves.
As the oval window pushes in the round window pushed out

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21
Q

Basilar membrane stiff at base, soft at apex

A

Apex: got the softest least stiff membrane
site 1 is at the stiffest

The basilar membrane is stiff at the base, and soft at the apex. The stiff has a resonance frequency that is going to be very high. high freq at base

Low freq at apex –> floppy things tend to vibrate at low freq
The traveling wave is giving maximum deflection between sites 2 and 3.
Lower freq cause areas 5 and 6 to vibrate

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22
Q

What happens at low freq:

A

Get the biggest movement at the apex, for 25 Hz you get very little vibration until you get to apex.

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23
Q

What happens at a higher freq sound

A

Get movement closer to base –> stapes
closer distance from stapes when vibrating

24
Q

Organ of Corti:

A

Take mechanical vibration and turn it into mechanical activity.

25
Q

two kinds of hair cells:

A

Inner hair cells: sensory –> sending info into the central nervous system, their cilia are free to move
Outer hair cells: motor, cilia are anchored in TM bring info out
basilar membrane moving up and down

26
Q

Cilia sticks out of epithelium:

A

Transduction –> links between cilia of each row, these links open channels

27
Q

In a scale of media where hair cells are:

A

You have special fluid composition, scala media has a high external K+ in endolymph (scala media)

Depolarization by K+ in hair cells
Tight junctions in the epithelium

When the cilia are pushed, those tip links pull on K+ channels and open them. K+ flows in
When the cell depolarizes that opens Ca+ channels
Sensory neurons get synapsed by hair cells, get depolarized, and fire action potentials.

28
Q

Inward current causes depolarization

A

When they return to normal cell hyperpolarizes, and as sound moves basilar membrane the hair cell membrane potential goes up and down

29
Q

Inward current causes depolarization

A

When they return to normal cell hyperpolarizes, and as sound moves basilar membrane the hair cell membrane potential goes up and down

30
Q

What happens above 3kHz

A

The cell will depolarize and stay depolarized, the constant shift in cell potential.
AC is changing
Hair cell membrane potential can reflect frequency in a limited frequency range

31
Q

Outer hair cells

A

Anchored in the tectorial membrane, receives synapses from motor axons carrying info out. They tune frequency, outer hair cells contract in response to depolarization they are capable of generating force and amplify response of basilar membrane: response to low amplitude

32
Q

Tuning curve: which frequency can activate the cell with the quietest sound?

A

The quietest sound that will activate this neuron is about 2,000 kHz

33
Q

What would you expect for the tuning curve at the apex? (purple)

A

Lower freq bc at the apex of the mechanical structure of the basilar membrane will vibrate best at lower freq. Tuning curve depends where you are coming from in cochlear

34
Q

Inner ear extracts freq info

A

Tonotopy: frequency mapped in space

35
Q

Encoding frequency in auditory nerve:

A

the auditory nerve can follow low frequencies ( < 3 kHz)
the brain needs to know how many volleys happen
The hair cells depolarize and stay depolarized at a higher frequency
Labeled line –> maintain info by connecting with proper parts.

35
Q

Encoding frequency in auditory nerve:

A

the auditory nerve can follow low frequencies ( < 3 kHz)
the brain needs to know how many volleys happen
The hair cells depolarize and stay depolarized at a higher frequency
Labeled line –> maintain info by connecting with proper parts.

36
Q

What does the ear hear? Nerve encodes:

A

Labeled lines –> telling us what the frequency is
Loudness –> frequency of action potentials in axons
Phase –> low freq we have a burst of action potentials that are locked to the phase of the cell coming in

37
Q

Transmitting auditory information to brain

A

Axons go to cochlear nuclei in medulla

38
Q

Central targets of auditory information

A

binaular targets (olivary) input from both ears

39
Q

In cochlear Nuclei:

A

Ventral (AVCN –> anterior ventral cochlear nuclei and PVCN –> posterior ventral cochlear nucleus) go to olivary nuclei (localization)

40
Q

Location of sound:

A
  • Elevation: where it is up and down
  • Azimuth –> 360 degree horizontal plane
41
Q

Azimuth:

A

Two binaural cues:
-Intensity (loudness) head as “shadow” or sound barrier

-Timing of sounds arriving at each ear👂 timing differences as small as 10 μs can be detected.

42
Q

Azimuth 1: Interaural time difference (ITD)

A

sound arrives at two ears at different times
sound from two ears combines in MSO:
- new stimulus variable of ITD
- circuit made up of delay lines and coincidence detectors
5 neurons –> They detect the time of arrival of the action potential from two sides.
A will be activated if the right ear gets the sound first
E will get the action potential at the same time if the left ear gets the sound first
Jeffress 1948

43
Q

The MSO coincidence detector:

A

Loud speaker, right and left ear
Loud speaker is closer to the left ear, so sound will reach the left ear first
That will cause an action potential in the auditory axon which will then activate the cochlear nucleus axon that’s going to go to MSO
Later the sounds arrive on the right side
Each axon sends a branch to neurons

44
Q

When action potential gets all the way to 5:

A

The terminal will release transmitters onto E, and at the same time action potential from the right side arrives and is released, E is excited and sends an action potential to the inferior
left ear first, right ear later

45
Q

When action potential gets all the way to 5:

A

The terminal will release transmitters onto E, and at the same time action potential from the right side arrives and is released, E is excited and sends an action potential to the inferior
left ear first, right ear later

46
Q

The cell that fires most strongly (A,B,C,D,E) will tell you:

A

-Which ear heard the sound first
E fired indicating left ear heard it first

-Time difference
If right and left had been closer then E would have fired action potential from right would have been arriving sooner

47
Q

Locate the source of sound in 3 dimensional space

A

A sound coming from the left side of the head will reach the left ear before it reaches the right ear.

48
Q

Phase locking

A

Phase information from spike trains that are phase-locked
Information in the burst action potentials, each burst is phase-locked to the sound.
For every beat of sound you get a burst of action potential and compare time

49
Q

If the right is leading and left is lagging

A

The burst in action potential on left will arrive later, each cycle gives an opportunity for comparison in time difference. For a continuous sound you can tell where it is, MSO will compare the time of arrival of the burst action potential.

50
Q

How do we locate high frequencies?

A

Our auditory nerve can’t follow frequencies about 3,000 Hz

51
Q

Azimuth 2: Interaural level difference (ILD)

A

Sound from two ears is combined to create loudness difference
-inhibition from opposite ear & excitation from same side ear

52
Q

What if sound is coming out from the left?

A

It gets more excited then it gets inhibited
The closer to the midline it gets the closer to inhibition it gets, and both ears are going to be getting equal loudness so inhibition and excitation will cancel out.

53
Q

Auditory cortex

A

Projections to and from A1 are tonotopic
Certain sounds are much more excitatory for a number of cells

54
Q

Major Language Areas:

A

Broca’s Area: language protection
Wernicke’s area: language comprehension

55
Q

What happens if you damage Wernicke’s area?

A

You will not understand speech, and may produce sounds like speech, comprehension is still okay.

Neuro (7 decks)

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