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Neuro > The auditory system 09.02.23 > Flashcards

The auditory system 09.02.23 Flashcards

1
Q

What is sound?

A

The displacement of air particles following a sinusoidal pattern of compression and rarefacation

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2
Q

What does a bigger amplitude mean for sound?

A

The bigger the amplitude of the sound wave, the louder the sound

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3
Q

What is the range of human hearing?

A

20Hz - 20KHz
- This range will change during our life

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4
Q

How is sound transferred or moved in the outer, middle and inner ear?

A

Outer - air
Middle - air
Inner - fluid

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5
Q

What is the pinna?

A

It is the cartilaginous structure that we can see on the outside of the ear

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6
Q

How is the pinna formed?

A
  • From pharyngeal arches 1 and 2
  • It has 6 Hillocks of His
  • Formed between the 10th and 18th week in utero
  • The outer ear forms independently to the inner ear
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7
Q

What is the role of the pinna?

A
  • It directs sound waves towards the ear canal
  • It has folds in the ear that selectively filters sounds
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8
Q

What is the ear drum also called?

A

The tympanic membrane

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9
Q

What shape is the eardrum?

A

It is not flat but curved towards us

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10
Q

What are the top 1/3 and bottom 1/3 of the eardrum called?

A

Top: Pars Flaccida
Bottom: Pars Tensa

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11
Q

How big is the eardrum?

A

8 x 10mm diameter
14mg
84mm2 - 55mm2
(About the size of your pinky fingernail)

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12
Q

What are the three bones in the middle ear called?

A
  • Malleus
  • Incus
  • Stapes
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13
Q

What are the two muscles in the middle ear called?

A
  • Tensor Tympani
  • Stapedius
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14
Q

What is the tube in the middle ear called?

A

Eustachian tube

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15
Q

What is the role of the middle ear?

A

Acoustic impedance match between air and fluid-filled inner ear
(converting air to fluid)

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16
Q

How much energy is lost transferring air to fluid?

A

97%

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17
Q

How does the middle ear create a sound vibration?

A
  • The eardrum is concentrating sound onto a small area (area of stapes) (14:1 SA difference)
  • This amplification makes it louder
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18
Q

How does the ossicles create a movement?

A
  • It acts as a lever
  • Creating a moment force which in turn creates a small force onto the stapes
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19
Q

How much longer is the handle of malleus compared to the incus?

A

1.3 times longer

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20
Q

What is the role of muscles in the middle ear?

A
  • They protect the inner ear from acoustic trauma
  • Stiffens the ossciular chain
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21
Q

What does the stapedius muscle do?

A
  • It is stimulated acoustically
  • It has a reflex arc of 3 or 4 neurons
  • 25ms reaction time
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22
Q

What does the tensor tympani do?

A

It tenses the tympanic membrane
- Helps us be able to hear other sounds while chewing

23
Q

What is the eustachian tube?

A
  • tube that causes crackling
  • We pop this tube on an aeroplane
24
Q

What is the role of the eustachian tube?

A
  • ventilation of the middle ear space
  • Drains secretions
  • Often dysfunctional in children
25
Q

What is the vestibulocochlear apparatus in the inner ear?

A
  • A set of fluid filled sacs, encased in bone
26
Q

What is the cochlear responsible for?

A

Hearing

27
Q

What is the labyrinth responsible for?

A

Balance

28
Q

What nerve innervates the vestibulocochlear apparatus?

A

The Vestibulocochlear nerve

29
Q

What is the structure of the cochlea?

A

2.5 turns of fluid filled bony tube

30
Q

What are the two openings of the cochlea?

A
  • Round window
  • Oval window
31
Q

What are the three compartments of the cochlea?

A
  • Scala Tympani
  • Scala Media
  • Scala Vestibuli
32
Q

What fluids are in the cochlea?

A

2 ionic fluids:
- Endolymph (High K+) - in the Scala media
- Perilymph (Na + rich) - in the Scala tympani and vestibuli

33
Q

How is a gradient maintained with ionic fluids in the cochlea?

A
  • Na, K-ATPase channel
  • NKCC1 and CIC-K chlorine channels
34
Q

How is a pressure wave created in the cochlea?

A

The oval window moves and creates a pressure wave

35
Q

Where does the pressure wave travel in the cochlea?

A
  • Through the oval window
  • Into the Scala vestibuli
  • Through the helicotrema
  • Through the Scala tympani
  • Then through the round window
36
Q

What does the movement through the round window do?

A

Moves the cochlear as it passes through the basilar membrane and creates a movement up

37
Q

Where does the organ of Corti sit?

A

On the basilar membrane

38
Q

What does the organ of Corti contain?

A

Has hair cells in it that attach to the tectorial membrane

39
Q

What is the structure of the basilar membrane?

A
  • Narrow, stiff at base so high frequencies are detected here (at oval window)
  • Wide, floppy at the apex so low frequencies detected here (helliocotremor)
40
Q

What is tonotopy?

A

The spatial arrangement of where sound is perceived, transmitted, or received on the basilar membrane

41
Q

How do the hairs interact with the membranes and their movements?

A
  • The basilar membrane moves up due to pressure
  • The Organ of Corti and the hairs move with it taking the pressure so that the…
  • … Tectorial membrane does not move
42
Q

What does the inner and outer hair cells cause a change in energy of?

A

Inner hair cell: Changes energy from mechanical (fluid) to electrical
Outer hair cell: Fine tuning

43
Q

What occurs at the stereocillia?

A
  • These are anchored to the tectorial membrane.
  • They have shearing forces so brush against it
  • They convert physical force from sound, head movement or gravity into an electrical signal, a process that is called mechanoelectrical transduction
44
Q

What does movement of the stereocillia cause?

A
  • A rapid response is required
  • K+ channels open causing depolarisation
  • Results in calcium channels open
  • Influx of calcium
  • Releases neurotransmitter
  • Repolarisation
45
Q

How does outer hair cells help us respond to specific frequencies?

A

Outer hair cells alter the stiffness of the basilar membrane to ensure maximal stimulation at one site and a dampened response at another
- Hair cells not activated droop and pull tectorial membrane down so it is only up at one activation point

46
Q

How is frequency/ pitch encoded for neural transmission?

A

In nerves by location along the basilar membrane

47
Q

How is intensity/ loudness encoded for neural transmission?

A

In nerves by numbers responding and by firing rate

48
Q

How is sound transduction encoded for neural transmission?

A

By inner hair cells

49
Q

How is amplification encoded for neural transmission?

A

Outer hair cells

50
Q

How is sound transmitted from neuron to the brain?

A

Auditroy fibre to spiral ganglion to cochlear nerve (8th) to the central auditory pathway to medial geniculate body to auditory cortex

51
Q

What does the brainstem do?

A

Sound localisation

52
Q

What is sound localisation?

A

Brainstem has a coincidence detector because sound may reach one ear quicker than the other and it needs to localise that sound into one sound

53
Q

What is the structures of the central auditory pathway?

A

ECOLI
E - Eight nerve
C - Cochlear nucleus
O - Olive (superior olivary nucleus)
L - Lateral leminiscus (contralateral cross)
I - Inferior colliculus

Then to the thalamus and then primary auditory cortex

Neuro (35 decks)

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