Sound Conduction and Transduction

Question 1

What scale is used to measure how loud a sound is?

Answer 1

Decibels (logarithmic scale)

Question 2

What is pitch? What is the audible range for humans in terms of frequency?

Answer 2

Perception of frequency

20-20,000 Hz

Question 3

What is the name given to the wing shaped flap of skin and cartilage that makes up the outer ear?

Answer 3

Pinna

Question 4

Describe the shape of the outer ear and its importance.

Answer 4

Conical: starts off wide at the external auditory meatus + narrows to the tympanic membrane
This focuses the noise + increases the pressure on the tympanic membrane

Question 5

Is the tympanic cavity fluid-filled or air-filled? What is its function?

Answer 5

Air-filled
Transmits vibrations of tympanic membrane across the cavity to the internal ear; accomplished by 3 interconnected but moveable bones (ossicles)

Question 6

How do the ossicles increase the pressure of vibration of the tympanic membrane to match the impedance and reduce energy loss?

Answer 6

Incus has a flexible joint with the stapes, the resulting lever action increases force on the oval window
Stapes vibrates against superior oval window to induce pressure wave in inner ear fluid
Round window acts as a pressure release window- moves outwards to equalise pressure when stapes pushes oval window into cochlea

Question 7

What is the point of the middle ear? Why isn’t the tympanic membrane continuous with the cochlea?

Answer 7

Cochlea contains fluid, in which you are trying to induce a pressure wave
If tympanic membrane was continuous with the cochlea, you would go straight from air to fluid + most of the energy will bounce back due to impedance
Sound waves require more energy to travel through fluid than air so the increase in pressure of vibration is crucial for this conduction

Question 8

What 2 muscles are involved in making sure that the ossicles aren’t damaged by excessive vibration due to loud noise? What is the name given to this reflex?

Answer 8

Reflex contraction of Tensor Tympani + Stapedius reduce amplitude of vibrations passing through ossicles
Auditory reflex

Question 9

What does displacement of stereocillia cause?

Answer 9

Opening of ion channels, depolarisation/ hyper polarisation of the nerve synapsing the hair cells
Bending of stereocillia towards the tallest stereocillium changes the internal voltage of the cell producing an electrical signal that goes to the brain (mechanotransduction)

Question 10

What is the latency period of the auditory reflex?

Answer 10

50-100 ms

Question 11

What is hyperacusis?

Answer 11

Painful sensitivity to low intensity sounds – can occur in conditions that lead to flaccid paralysis of the auditory reflex muscles (e.g. Bell’s Palsy)

Question 12

Which test is used to determine the site of damage to the auditory system, that is causing hearing loss?

Answer 12

Weber Test

Question 13

What are the 2 specialised membranes of the cochlea?

Answer 13

Oval Window

Round Window

Question 14

What are the 3 chambers of the cochlea? What type of fluid does each contain?

Answer 14

Scala Vestibuli- Perilymph
Scala Media- Endolymph
Scala Tympani- Perilymph

Question 15

What is the difference in composition of perilymph and endolymph?

Answer 15

Perilymph: Low K+, High Na+
Endolymph: High K+, Low Na+

Question 16

What structure connects the 2 perilymph chambers?

Answer 16

Helicotrema

Question 17

Describe the mechanism of sound transduction

Answer 17

Vibration of tympanic membrane moves malleus + incus laterally, pushing the stapes medially onto the oval window, generating a wave in the fluid filled cochlea
The wave moves through the cochlea causing 2ndary tympanic membrane to bulge leading to vibration of the basilar membrane + stimulation of receptor cells

Question 18

Describe the difference in sensitivity of different parts of the basilar membrane.

Answer 18

Higher frequency sounds = base

Lower frequency sounds = apex

Question 19

What is the Organ of Corti?

Answer 19

Sense organ of the cochlea, which converts sound signals into nerve impulses that are transmitted to the brain via the cochlear nerve

Question 20

Where is the Organ of Corti found?

Answer 20

It lies on top of the basilar membrane + beneath the tectorial membrane

Question 21

What are the 2 types of cell in the organ of corti?

Answer 21

Inner + outer hair cells

Question 22

Describe 6 features and the function of inner hair cells.

Answer 22

Found alone
Not in contact with tectorial membrane
Send afferents to brain- provide sensory transduction
~3500 per cochlea
Function:
Have stereocilia that move in response to the movement of endolymph in the scala media
Transmit auditory stimulus

Question 23

Describe 5 features and the functions of outer hair cells.

Answer 23

Found in groups of 3 
In contact with tectorial membrane  
Receive efferents from brain 
Vulnerable to damage (can result in sensorineural hearing loss)
~11,000 per cochlea 
Function: 
Electromotile so can expand + contract to amplify the amount of vibration
Control of inner hair cells

Question 24

Which compartment of the cochlea does the stereocilia of the hair cells project into?

Answer 24

Endolymph (base is in the perilymph)

Question 25

What internally generated sounds are the outer hair cells responsible for?

Answer 25

Otoacoustic emissions

Question 26

What are stereocilia connected by? What do these act as? What is activated by stretching these?

Answer 26

Tip links Act as small springs stretched by stereocillia sliding Stretching results in opening of ion channels + response currents

Question 27

What bony conical structure is found at the middle of the cochlea?

Answer 27

Modiolus

Question 28

Describe what happens when the basilar membrane is displaced upwards.

Answer 28

Depolarisation Stereocilia move away from the modiolus K+ channels open K+ enters from endolymph

Question 29

Describe what happens when the basilar membrane is displaced downwards.

Answer 29

Hyperpolarisation Stereocilia move towards the modiolus K+ channels close

Question 30

What separates scala vestibuli + scala media? What separates scala media + scala tympani?

Answer 30

Scala Vestibuli-Scala Media: Reissner's (vestibular) membrane Scala Media-Scala Tympani: Basilar membrane

Question 31

Describe the central auditory pathway to the primary auditory cortex.

Answer 31

``` Hair cells depolarise Synapse with neurones in spiral ganglion Cochlear division of CNVIII synapses with the ipsilateral cochlea nucleus in medulla (dorsally + ventrally) - transmission onwards is bilateral Superior olivary nucleus Inferior colliculus Medial geniculate nucleus Auditory cortex ```

Question 32

Up to what point is the auditory pathway from one ear ipsilateral?

Answer 32

Cochlear nuclei | Beyond this point there is bilateral representation

Question 33

The inferior colliculus receives input from both cochlea. What is the inferior colliculus responsible for?

Answer 33

Reflex associations: turning your head towards loud noise

Question 34

Describe a phenomenon that is involved in sharpening the signal coming from the cochlea.

Answer 34

Lateral inhibition

Question 35

To which parts of the CNS do collaterals from the auditory pathway go?

Answer 35

Reticular formation | Cerebellum

Question 36

In which lobe is the primary auditory cortex?

Answer 36

Temporal

Question 37

What is the secondary auditory cortex responsible for?

Answer 37

Responding to sounds coming off/on | Responding to the duration of sound

Question 38

What is the name given to the axons that project from the medial geniculate nucleus to the primary auditory cortex?

Answer 38

Acoustic radiations (travel via the internal capsule)

Question 39

How do you localise short sound burst? | How do you localise continuous sound?

Answer 39

Short: Interaural time delay Continuous: Interaural intensity difference

Question 40

What is conductive hearing loss?

Answer 40

Middle ear damaged Ear not capable of transmitting vibration of sound waves onto cochlea Amplification system is eliminated

Question 41

What is sensorineural hearing loss and what can it be caused by?

Answer 41

Cochlea/ cochlear nerve damaged | Signal transmitted to the primary auditory cortex is reduced/ lost

Question 42

What is the term used to describe loss of hearing due to the death of hair cells in normal ageing?

Answer 42

Presbyacusis

Question 43

What is Timbre?

Answer 43

What distinguishes 2 sounds at the same frequency + intensity

Question 44

What is the hair bundle?

Answer 44

A cluster of modified microvilli called Stereocillia

Question 45

What does impedance measure?

Answer 45

Reluctance of a system in receiving energy from a source

Question 46

What is resonant frequency?

Answer 46

Frequency at which the impedance of the system is minimal

Question 47

What is effected in conductive hearing loss? List 4 causes

Answer 47

Outer + middle ear Ear is not capable of transmitting the vibration of sound waves onto the cochlea Fluid accumulation in inner ear, perforated tympanic membrane, ostosclerosis + barotrauma

Question 48

What generates a difference in pressure between the 2 liquid filled chambers of the cochlea? What is the consequence of this?

Answer 48

Motion of the Stapes | Causes vibration of basilar membrane

Question 49

What is the Organ of Corti comprised of?

Answer 49

Basilar + Tectorial membranes Hair cells Supporting cells

Question 50

Define intensity and volume

Answer 50

Intensity: Amplitude of sound waves Volume: Perception of amplitude

Question 51

What is the external ear composed of?

Answer 51

Pinna (Auricle) External acoustic meatus (auditory canal) Tympanic membrane (ear drum)

Question 52

Name the auditory ossicles and describe their connections

Answer 52

Malleus: connected to tympanic membrane Incus: connected to malleus by synovial joint Stapeus: connected to Incus by synovial joint + attached to lateral wall of the internal ear at oval window

Question 53

What is the internal ear composed of?

Answer 53

``` Bony labyrinth (3 parts- vestibule, semi-circular canals, cochlea) Membranous labyrinth (Membraneous ducts + sacs within bony cavities) ```

Question 54

What is the bony labyrinth lined and filled with?

Answer 54

``` Lined with periosteum Fluid filled (perilymph) ```

Question 55

List the components of the membraneous labyrinth and their functions. What are these spaces filled with?

Answer 55

Semi-circular ducts: balance Cochlear duct: Hearing 2 sacs: Utricle + Saccule: Balance All filled with endolymph

Question 56

How is sound amplified by the structure of the tympanic membrane and oval window?

Answer 56

Focussing the vibrations from large SA of tympanic membrane to small SA of oval window Decrease in SA results in pressure increase

Question 57

What maintains the concentration gradient of Na+ and K+ between the different cochlea compartments?

Answer 57

Stria vascularis

Question 58

Describe the difference in fibres on the basilar membrane

Answer 58

``` Base= Short + stiff - vibrate in response to high frequency End= Long + loose - vibrate in response to low frequency ```

Question 59

What is meant by tonotopic mapping?

Answer 59

Different parts of auditory cortex for different pitches Low frequencies = ventral neurones High frequencies = dorsal neurones

Question 60

What can cause conductive hearing loss?

Answer 60

``` Wax Infection Otoscleorisis of ossicles Perforated tympanic membrane Barotrauma Fluid accumulation ```

Question 61

State 3 causes of pre-lingual hearing loss

Answer 61

Perinatal/ bacterial meningitis Congenital infection e.g. rubella Head injury

Question 62

State 6 common causes of hearing loss in adults

Answer 62

``` Genetics Ototoxicity (chemotherapy) Infection Tumour Head injury Loud noises ```

Question 63

Name 1 solution to address the loss of hair cells causing hearing loss

Answer 63

Bypass dead cells + stimulate nerve fibres directly with cochlear implants