The auditory system 09.02.23

Question 1

What is sound?

Answer 1

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

Question 2

What does a bigger amplitude mean for sound?

Answer 2

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

Question 3

What is the range of human hearing?

Answer 3

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

Question 4

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

Answer 4

Outer - air
Middle - air
Inner - fluid

Question 5

What is the pinna?

Answer 5

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

Question 6

How is the pinna formed?

Answer 6

• 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

Question 7

What is the role of the pinna?

Answer 7

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

Question 8

What is the ear drum also called?

Answer 8

The tympanic membrane

Question 9

What shape is the eardrum?

Answer 9

It is not flat but curved towards us

Question 10

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

Answer 10

Top: Pars Flaccida
Bottom: Pars Tensa

Question 11

How big is the eardrum?

Answer 11

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

Question 12

What are the three bones in the middle ear called?

Answer 12

• Malleus
• Incus
• Stapes

Question 13

What are the two muscles in the middle ear called?

Answer 13

• Tensor Tympani
• Stapedius

Question 14

What is the tube in the middle ear called?

Answer 14

Eustachian tube

Question 15

What is the role of the middle ear?

Answer 15

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

Question 16

How much energy is lost transferring air to fluid?

Answer 16

97%

Question 17

How does the middle ear create a sound vibration?

Answer 17

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

Question 18

How does the ossicles create a movement?

Answer 18

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

Question 19

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

Answer 19

1.3 times longer

Question 20

What is the role of muscles in the middle ear?

Answer 20

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

Question 21

What does the stapedius muscle do?

Answer 21

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

Question 22

What does the tensor tympani do?

Answer 22

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

Question 23

What is the eustachian tube?

Answer 23

• tube that causes crackling
• We pop this tube on an aeroplane

Question 24

What is the role of the eustachian tube?

Answer 24

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

Question 25

What is the vestibulocochlear apparatus in the inner ear?

Answer 25

- A set of fluid filled sacs, encased in bone

Question 26

What is the cochlear responsible for?

Answer 26

Hearing

Question 27

What is the labyrinth responsible for?

Answer 27

Balance

Question 28

What nerve innervates the vestibulocochlear apparatus?

Answer 28

The Vestibulocochlear nerve

Question 29

What is the structure of the cochlea?

Answer 29

2.5 turns of fluid filled bony tube

Question 30

What are the two openings of the cochlea?

Answer 30

- Round window - Oval window

Question 31

What are the three compartments of the cochlea?

Answer 31

- Scala Tympani - Scala Media - Scala Vestibuli

Question 32

What fluids are in the cochlea?

Answer 32

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

Question 33

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

Answer 33

- Na, K-ATPase channel - NKCC1 and CIC-K chlorine channels

Question 34

How is a pressure wave created in the cochlea?

Answer 34

The oval window moves and creates a pressure wave

Question 35

Where does the pressure wave travel in the cochlea?

Answer 35

- Through the oval window - Into the Scala vestibuli - Through the helicotrema - Through the Scala tympani - Then through the round window

Question 36

What does the movement through the round window do?

Answer 36

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

Question 37

Where does the organ of Corti sit?

Answer 37

On the basilar membrane

Question 38

What does the organ of Corti contain?

Answer 38

Has hair cells in it that attach to the tectorial membrane

Question 39

What is the structure of the basilar membrane?

Answer 39

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

Question 40

What is tonotopy?

Answer 40

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

Question 41

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

Answer 41

- 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

Question 42

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

Answer 42

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

Question 43

What occurs at the stereocillia?

Answer 43

- 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

Question 44

What does movement of the stereocillia cause?

Answer 44

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

Question 45

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

Answer 45

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

Question 46

How is frequency/ pitch encoded for neural transmission?

Answer 46

In nerves by location along the basilar membrane

Question 47

How is intensity/ loudness encoded for neural transmission?

Answer 47

In nerves by numbers responding and by firing rate

Question 48

How is sound transduction encoded for neural transmission?

Answer 48

By inner hair cells

Question 49

How is amplification encoded for neural transmission?

Answer 49

Outer hair cells

Question 50

How is sound transmitted from neuron to the brain?

Answer 50

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

Question 51

What does the brainstem do?

Answer 51

Sound localisation

Question 52

What is sound localisation?

Answer 52

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

Question 53

What is the structures of the central auditory pathway?

Answer 53

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