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Ps The Nervous System > L23 Hearing And The Ear > Flashcards

L23 Hearing And The Ear Flashcards

1
Q

Define sound

A

Longitudinal pressure waves travelling through air or other medium

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2
Q

What is frequency?

A

Pitch of sound
- measured in Hertz = cycles per second

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3
Q

What is amplitude?

A

Intensity - loudness
- measured in decibels
- log scale to better match perception

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4
Q

What is the equation for frequency?

A

Freq = 1/t
Units = hertz/s-1

t = period/s

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5
Q

What is the middle ear?

A

It is air filled space
- needs equal pressure either side of the tympanic membrane otherwise hearing is impaired

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6
Q

Why do we need a middle ear?

A
  • sound waves travelling from air to water are mostly reflected
  • inner ear is fluid filled
  • without middle ear there’s a poor transfer of energy from air to cochlear fluid
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7
Q

What can the middle ear overcome and how?

A

Overcomes air-fluid mismatch
- ossicles act as levers
- area of tympanic membrane > footplate of the stapes

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8
Q

How many hair cells do human ears have?

A
  • one row of inner hair cells
  • three rows of outer hair cells
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9
Q

What are at the tips of hair cells?

A

Small processes called stereocilia
- bend in response to pressure changes
- stereocilia of the tallest row of outer hair cells are embedded in the tectorial membrane

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10
Q

In which direction ones the travelling wave move?

A

Moves from the base to the apex

Base - stiff - high frequencies
Apex - floppy - low frequencies

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11
Q

What happens when sound enters the cochlea?

A
  • the basilar membrane vibrates
  • travelling waves travel up the basilar membrane
  • position of maximal displacement depends on frequency of sound
  • low freq produce maximal displacement at the apex of cochlea
  • high freq produce maximal displacement at the base
  • displacement of basilar membrane excites hair cells
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12
Q

What does the excitation of inner hair cells lead to?

A

Leads to transmitter release and excitation of auditory nerve fibres

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13
Q

What happens when stereocilia bend towards to longest one?

A

Entry of K+ leads to depolarisation, Ca2+ entry and transmitter release

-> transmitters activate nerve fibres

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14
Q

What happens when stereocilia bend towards the shortest one?

A

No K+ entry leads to:
Hyperpolarisation
No transmitter
Nerves stop firing

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15
Q

How are inner and outer hair cells activated?

A
  • movement of basilar membrane + interaction with tectorial membrane
  • bending towards tallest stereocilium
  • bending towards shortest stereocilium
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16
Q

How are only inner hair cells activated?

A
  • release of neurotransmitters
  • activate cochlea nerve fibres associated with the hair cell
17
Q

How does the cochlea filter by frequency?

A
  1. Each neuron responds best to one frequency
  2. Each location along the cochlea amplifies one frequency
18
Q

How can outer hair cells be damaged?

A

Damaged by ototoxic drugs
- some antibiotics

19
Q

How do outer hair cells act as cellular motors?

A
  • change length as stereocilia bend back and forth
  • shorten and lengthen in response to sound stimulation
  • driven by motor protein in OHC membrane - Preston
  • inject energy and amplify basilar membrane movement
  • the reason hearing is so sensitive - detect BM movements in nm range
20
Q

What increases the displacement of basilar membranes?

A

The elongation and shortening of outer hair cells
- enhances hearing sensitivity and frequency selectivity

21
Q

At what sound pressure level is the threshold for hearing damage?

A

90dB

22
Q

What is the main function of the pinna?

A

Localisation of sound

23
Q

How are inner hair cells involved in the excitation of auditory nerves?

A

They release neurotransmitters as stereocilia bend towards the tallest

24
Q

Which structure of the cochlea changes shape due to the Preston protein and increases sound sensitivity?

A

Outer hair cells
- outer hair cells increase in length due to stereocilia bending
- this injects energy into the basilar membrane so it can vibrate more
- increases sensitivity to sound

25
Q

The stapedius muscle connects to which cranial nerve?

A

Stapes (CN VII)

26
Q

What is the role of the stapedius muscle?

A

It dampens the amplitude of the sound wave

27
Q

The tensor tympani muscle connects to which cranial nerve?

A

Malleus (CN V)

Ps The Nervous System (4 decks)

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