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Human physiology > Hearing > Flashcards

Hearing Flashcards

1
Q

How does sound travel?

A

Via longitudinal waves in the air

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2
Q

What are longitudinal waves?

A

Changes in air pressure- has areas of compression (peaks) and rarefraction (troughs)

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3
Q

What is the eardrum also known as?

A

Tympanic membrane

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4
Q

Where do sound waves travel in humans?

A

Ear canal- sound waves vibrate off of ear drum

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5
Q

How sensitive is our hearing and what frequencies can we hear?

A

Very sensitive- can detect signals that vibrate ear drum by a few picometres- amplifies signals by more than 100 fold

  • can hear frequencies of 20Hz - 20000Hz
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6
Q

What are the 3 small ear bones in the inner ear and where are they located?

A

Malleus
Incus
Stapes

  • create sound waves with varying frequencies in the perilymph of cochlea
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7
Q

What is the perilymph?

A

Type of extracellular fluid with components (e.g. sodium, potassium) similar to normal extracellular fluid

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8
Q

What does the active process enhance and what is this?

A

Frequency selectivity = capacity to discriminate between similar tones

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9
Q

What is the organ of corti and where is it found?

A

= strip of sensory epithelium running 33mm along the spiral cochlea

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10
Q

What is the key component of the organ of corti?

A

Hair cells = sensory receptors of inner ear

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11
Q

How many hair cells does the organ of corti contain?

A

16000

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12
Q

How are the hair cells in the organ of corti arranged?

A

one row of inner hair cells (IHCs) + 3 rows of outer hair cells (OHCs)

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13
Q

Describe the structure of the organ of corti

A

Made up of tectorial + basilar membrane
Hair cells lie within these 2 membranes with the IHCs connected to auditory nerve

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14
Q

What is the tectorial membrane and what is it attached to?

A

= extracellular matrix that covers the apical surface (highest point) of the organ of corti
- attached to stereocilia of OHCs

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15
Q

Why does the sound wave need to be amplified?

A

sound waves travel at different speeds in air vs perilymph

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16
Q

Define: amplification

A

The process of increasing the volume of sound

17
Q

What chamber is the perilymph located in?

A

Scala vestibuli

18
Q

How do sound waves travel through the perilymph?

A
  1. Stapes transmit sound waves through to the scala vestibuli
  2. Sound wave activates hair cells within organ of corti depending on the frequency
19
Q

What are the 2 different fluids in the organ of corti and where are they found?

A

Perilymph- scala vestibuli + scala tympani
Endolymph- scala media

20
Q

What is the main difference between the 2 fluids in organ of corti?

A

Endolymph has higher potassium content

21
Q

What is the basilar membrane and what happens when it vibrates?

A

= extracellular matrix that covers the basal surface (lowest point) of the organ of corti

Vibration =
1. Hair cells deflected = stereocilia move in a back and forth direction
2. = opens mechanically-gated ion channels = hair cell depolarisation releasing action potentials = converting sound wave into electrochemical signal

22
Q

What are the 3 chambars in the organ of corti?

A

Scala vestibuli
Scala media = cochlear duct
Scala tympani

23
Q

What is ear hair cell morphology optimised for?

A

Mechanosensation

24
Q

How are the hair cells optimised for mechanosensation?

A

Stereocilia within hair bundle are organised in rows of decreasing height
- bundle deflection only in direction of longest stereocilia leads to increased probability of mechanoreceptors opening

25
Q

What are mechanoreceptors?

A

= sensory receptors that respond to mechanical stimuli (touch, sound)

26
Q

Where is the kinocilium located?

A

Produced 1st during developmeny and moves to outer edge of top of hair cell as ear matures and then the stereocilia form

27
Q

Do stereocilia have a cytoskeleton and why?

A

They have a very structured actin cytoskeleton as they have to remain upright

28
Q

How are stereocilia connected?

A

via tip links that connect top of one stereocilia to another

29
Q

What are roolets and what is their function?

A

= actin filaments in stereocilia- anchor stereocilia into specialised actin network = cuticular plate

30
Q

What happens if certain proteins that make up tip links are removed?

A

Mechanosensitivity of stereocilia is decreased which could lead to deafness

31
Q

How can stereocilia be seen in a lab?

A
  1. Hair bundles stained with phalloidin
  2. Can be viewed via light or electron microscope depending on resolution
32
Q

Name and describe the model that explains how mechanotransduction works

A

THE TETHER MODEL:
1. Tip link connected to mechanosensitive channel
2. Tension causes channel to open = influx of calcium ions
3. Channels are also opened in other stereocilia
4. Adaption phase = motor protein slios down which relieves tension in tip link = mechanosensitive channel closes quickly
5. Upper tip link climbs up stereocilium to re-establish tension

33
Q

Name 2 proteins that form tip links

A

Protocadherin 15
Cadherin 23

34
Q

Name 2 places where mechanosensitive channels are located in the ear

A

Stereocilia
apical membrane

35
Q

What 2 TMCs are candidates for essential functioning of mechanoreceptor channels and whats the evidence for this?

A

TMC1 + TMC2:
- Both are selectively expressed in developing hair cells at the onset of mechanosensitivity
- Mutations of TMC1 = deafness
- Absense of both = hair cells of mice lack mechanosensory responses to forward deflection of hair bundles
- Transient exogenous expression of either restores mechanosensitivity in hair cells in mice who have had them knocked out

36
Q

How is the organ of corti adapted for function?

A

= gradual changes in structure + morphology from base to apex e.g. height of stereocilia + width and thickness of basilar membrane
- stiff and taute at base- picks up high frequencies
- More flaccid at apex- can move freely so picks up lower frequencies

37
Q

What happens when the cochlea recieves a pure tone acoustic stimulus?

A
  1. Pressure differences between its liqiud filled compartments cause basilar membrane to oscilate at frequency of stimulation
  2. Waves propagate from base of cochlea towards apex
  3. As wave progresses, it grows in amplitude but drecreases in wavelength and the quickly vanishes when it reaches relevant frequency position on basilar membrane
38
Q

Describe the active process

A

OHCs locally activated and enhance basilar membrane vibration

  1. Depolarisation causes OHCs to shorten as well as enhances vibrations via contractions and hyperpolarisation causes them to elongate
  2. IHCs detect the vibrations and activate afferent neurons e.g. auditory nerve
39
Q

Where are piezo2 channels found in the ear?

A

apical membrane

Human physiology (43 decks)

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