L08: Hearing

Question 1

What structures does the outer ear contain

Answer 1

Pinna
Auditory canal
Tympanic membrane

Question 2

What structures does the middle ear contain

Answer 2

Ossicles (3 small. Bones)

A connection to the Eustachian tube

Question 3

What structures does the inner ear contain

Answer 3

Cochlear

Semilunar canals

Question 4

What are the 3 small bones that form the ossicles

Answer 4

Malleus
Incus
Stapes

Question 5

What is the 2 roles of the 3 small bones in the middle ear

Answer 5

• Transmit sound wave form the tympanic membrane to the oval window of the inner ear
• amplify the sound they transmit the sound

Question 6

What is the oval window

Answer 6

The window that allows connection of the stapes bone to the inner ear

Question 7

How is the mechanism to reduce amplification of loud sound achieved

Answer 7

By 2 muscles of middle ear

Question 8

What are the 2 muscles of the middle ear

Answer 8

Strapedious muscle

Tensor tympani muscle

Question 9

What happens to these 2 muscles where there is loud sound

Answer 9

Contract

Question 10

What does the contraction of the 2 muscles allow

Answer 10

Stop amplification of sound via 3 bones- attenuation reflex

Question 11

What are the 3 tubes in the cochlear known as

Answer 11

Scala vestibuli
Scala media
Scala tympani

Question 12

What does the scala media contain

Answer 12

Organ of corti

Question 13

What lining separtes the scala media and scala tympani

Answer 13

Basilar membrane

Question 14

Where does the scala tympani and scala vestibuli connect to

Answer 14

Helicotrema (a hole at apex of ear)

Question 15

What liquid found inside the scala media

Answer 15

Endolymph

Question 16

What happens to the endolymph when the stapes pushes the oval window membrane in the cochlear

Answer 16

The endolymph moves back and forth

Question 17

As the endolymph moves what structure does it also move

Answer 17

The basilar membrane

Question 18

How does the rigidity of the basilar membrane change along its length

Answer 18

From narrow and stiff (at base) to wider and floppy (at apex)

Question 19

Which type of sound influences the apex

Answer 19

Low frequency sound

Question 20

What type of sound influences the base

Answer 20

High frequency sound

Question 21

Where is the organ of orti located

Answer 21

In the scala media on the basilar membrane

Question 22

Therefore when the basilar membrane moves what happens to the organ of corti

Answer 22

Organ of corti moves as the basilar membrane moves

Question 23

What type of cells are found at the organ of corti

Answer 23

Hair cells

Question 24

What membrane does the hair cells touch

Answer 24

Tectorial membrane

Question 25

What structure does the tectorial membrane also sit on top of

Answer 25

Sterocilia

Question 26

What is the sterocilia

Answer 26

A structure that sits on the hair cells

Question 27

As the organ of corti moves what happens to the tectorial membrane

Answer 27

It moves

Question 28

As the tectorial membrane moves what happens to the sterocilia

Answer 28

Moves

Question 29

What happens when sterocilia bend in and out

Answer 29

Open different ion channels

Question 30

If ion channels open on the hair called as a result of sterocilia bending what happens to the hair cells

Answer 30

Depolarisation

Question 31

On the outer/inner hair cell which specific channel opens to cause depolarisation as the stereocilia moves

Answer 31

Mechanically gates pottasium channels

Question 32

What happens to potassium when the mechanically gated potassium channels open

Answer 32

Potassium influx into the outer hair cell

Question 33

When there is a depolarisation in the outer/inner hair cell what channel opens

Answer 33

Voltage gated calcium channels

Question 34

What does calcium influx as a result of voltage gated calcium channels cause

Answer 34

Exocytosis of neurotransmitters (glutamate) in the pre-synaptic vesicles to the spiral ganglion neurite

Question 35

What does glumate get released to

Answer 35

Spiral ganglion neuritis

Question 36

What do many spiral ganglion cells form

Answer 36

The auditory nerve

Question 37

How many spiral ganglion cells transmit a signal from inner hair cell

Answer 37

Many (divergent)

Question 38

How many spiral ganglion cells connect to outer hair cells

Answer 38

Small number (convergent)

Question 39

What is the main role of outer hair cells of the organ corti

Answer 39

Amplify sound for inner hair cells

Question 40

How does outer hair cells amplify sound

Answer 40

1) Outer hair cells have motor proteins that contract and relax 2) when the motor protein contracts it pulls the stereocilia into one direction 3) pulling the stereocilia pulls the tectorial membrane with it 4) this amplify the sound by the inner hair cells

Question 41

What is tonotopy

Answer 41

Because the basilar membrane has different rigidity along its length from base to apex, every part of the membrane is responsive to a characteristic frequency that the hair cells are sensitive to

Question 42

What does the tonotopy organisation allow us to do

Answer 42

Distinguish sound at different frequency

Question 43

What is a characteristic frequency

Answer 43

Highest spikes the hair cell can produce in repsonse to its frequency that it is specific to

Question 44

Which ascending pathway takes the info from the ear to the brain

Answer 44

Auditory pathway

Question 45

Which side of the brain does info from the left ear go to

Answer 45

Both sides of the brain i.e left and right

Question 46

What side of the brain does info form the right ear go to

Answer 46

Both sides of the brain i.e left and right

Question 47

Where does info form the auditory pathway go to

Answer 47

Auditory cortex

Question 48

How is the auditory cortex organised

Answer 48

Tonotopy

Question 49

What does tonotopy of the auditory cortex mean

Answer 49

Specific frequency terminate at specific regions of the auditory cortex that correlates to that frequency

Question 50

What is the primary auditory cortex surrounded by

Answer 50

Secondary auditory cortex

Question 51

What is phase locking

Answer 51

Firing an action potential with every cycle of frequency sound

Question 52

When does phase locking occur

Answer 52

In low frequency sound

Question 53

Why is phase locking not possible in high frequency

Answer 53

The sensory neurones cannot be continuously stimulates to produce rapid cycles of action potential

Question 54

What limits the phase locking in high frequency sound

Answer 54

Refractory period of the nerve cells

Question 55

What do we rely on for high frequency sounds if phase locking doesn’t occur

Answer 55

Tonotopy (organisation of the auditory system)

Question 56

In loud sound what is the firing of spikes like

Answer 56

High

Question 57

In soft sound what is the firing of spike like

Answer 57

Low firing

Question 58

How can we localise sound

Answer 58

Message from the ipsilateral ear goes to the superior Olive quickly than the message from the other ear which reaches the superior olive slower due to it needing to pass to the other side = interaural delay

Question 59

What is another way of localising sound

Answer 59

When sound waves hit your head it creates a sound shadow, so the contralateral ear has a lower intensity than the ipsilateral ear,

Question 60

What is nerve deafness

Answer 60

Damage to the inner ear or auditory pathway

Question 61

What are the 3 main causes of nerve deafness

Answer 61

Genetic disorder: affected hair cell structures Congenital: congenital rubella syndrome, toxoplasmosis- lead to hypoplastic auditory nerves Presbycusis: normal age related loss (not reversible)

Question 62

What is acquired nerve deafness

Answer 62

Cochlear damage due to noise from environment or occupation

Question 63

Which drugs can damage the ear

Answer 63

Aminoglycosides (anitbiotics) | Methotrexate (immunosuppressant drugs)

Question 64

If the motor proteins in the outer hair cell contracts when there is no sound what can this cause

Answer 64

Tinnitus i,e noisy ear