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Flashcards in The auditory system Deck (37)
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1

Tell me about the scale of hearing loss? 

  • 1:6 projected to reach 1:5 
  • 11 million people with hearing loss in the UK (900,000 with severs or profound loss)  2035 15.6 million 

2

What are the aspirations for hearing loss?

What does this rely on?

Aspiration – preservation or maintenance of hearing across the lifecourse

This preservation relies on adequate function of the complete auditory system – implants also require adequate residual function.

3

What are hearing aids used for ?

Hearing aids – amplify, CIs – replace IHC function – no pharmacological intervention- mechanistic understanding needed 

4

What is sound characterised by?

Sound is characterised by its pitch (tone) and intensity (loudness) 

5

What are the two characteristics to sound?

Amplitude = loudness/volume

Frequency = Pitch/tone (human hearing range 20Hz – 20kHz, bats 20-200kHz)

6

Sound (or noises) scale in dB

whats considered good/ bad for hearing?

7

The human ear structure

8

Whats the role of the outer and middle ear?

  • outer and middle: transmit sound to the inner ear, also help compensate for the loss in sound energy that naturally occurs when the sound waves pass from air into water by amplifying the sound energy during the process of sound transmission
  • middle: The primary function of the middle ear is to offset the decrease in acoustic energy that would occur if the low impedance ear canal air directly contacted the high-impedance cochlear fluid

9

Whats the role of the inner ear?

inner: two jobs, changes sound waves to electrical waves (nerve impulses). Allows the brain to hear and understand sounds. Also important for balance 

10

What are the 3 tiny bones in the middle ear called, and what is their function?

3 bones in middle ear called Ossicles. They transmit sounds from the air to the fluid filled cochlea 

11

What are specialised sensory cells in the inner ear called?

Specialized sensory cells – hair cells - are located within the inner ear 

12

What are the key nuclei of the auditory pathway and what is their role?

The cochlea nuclei 

  • Cochlea and hair cells role in hearing 
  • Every step involves processing of the particular sound signal 
  • Cochlea has an aqueous environment 

13

When sound waves move from the air, tell me about the resistance?

The sound wave is moving from air, which has a low impedance (low resistance) to an aqueous environment in the inner ear which has a high impedance (high resistance) 

14

Tell me about the cochlea amplifier and how it works?

  • Cochlea amplifier is a positive feedback mechanism 
  • Causes the tip links of the OHC hair bundle to open allowing inflow of Na+ and K+ which depolarizes the OHC 
  • A lengthening of prestin lengthens the hair cell while prestin concentration leads to a decrease in OHC length 

15

The cochlea structure 

(has been unrolled in order for structure to be seen more clearly)

16

Tell me about the fluid filled cavities in the cochlea and what they are filled with?

  • Fluid filled cannels running beside each other but filled with different fluid e.g., perilymph and endolymph 
  • In healthy ear the endolymph has a higher potassium level 
  • Basal end of cells bathed in perilymph 
  • Endocochlea potential created from balance between potassium levels 

 

17

What are the layers of the hair cells 

18

Where are Stereocilia found?

around the inner and outer hair cells 

19

Tell me about the inner and outer hair cells 

  • Stereocilia are around the inner and outer hair cells 
  • Outer hair cells sit in little clusters or trios whereas the inner cells are the sensing cells and sit individually 
  • Inner cells sense the vibrations of sound and help you hear 

20

How are action potentials induced in the sensorys in the hair cells? 

21

Tell me about the basilar membrane of the hair cell?

  • Basilar membrane: tapered structure – narrow at one end and gets progressively wider along its length (at base of cochlea at the bottom of the curl)
  • Move towards top moves towards the low frequency end of the spectrum that we can perceive 
  • Topographical mapping of frequency allows us to distinguish between different frequencies/pitches
  • Spectral analysis- distinguish between different frequencies 

22

How does this vibrational energy in the basilar membrane get transduced into an electrical signal?

  • The mechanical movement of specialized (mechanotransduction)
  • sensory cells: hair cells
  • stereocilia is deflected to right from its central position as sound wave passes 

23

What in the hair cell structure is important for sound production?

  • small Tip link proteins connect… 
  • outer hair cells involved in amplification process of the cell and control part of movement of membrane. Part of sound management system 

24

Tell me about the tip link protein and what a mutation in this protein can cause 

  • mutation in tip link can make someone congenitally deaf- very important proteins 
  • tip links, when flexsion happens the mechanically gated channels open

25

Tell me aboutt he distortion open channels...

  • respond to movement of potassium
  • tip links move apart, depolarisation as a result activated 
  • relayed to cochlea nucleus 
  • interpreted into a sound 

26

Ionic bases of mechanotransduction

27

What are the two types of hair cells?

2 types of hair cells (inner – outer)

1. Inner = sensory receptors (transduction)

2. oHC contract and expand in response to

28

The electrical currents (active process) in the outer hair cells (OHC)

  • Electromotility
  • Depolarisation = Contraction
  • Hyperpolarisation = Relaxation

29

Whats the function of the outer hair cells?

Amplifies motion of basilar membrane enhances the responsiveness of inner hair cells

30

Whats the role of cochlea amplifiers?

Cochlear amplifiers: enhances amplitude and sharpness