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 the audible range for humans in terms of frequency?

Answer 2

20-20,000 Hz

Question 3

What is the name given to the wing shaped flap 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

It is conical – starts off wide at the external auditory meatus and narrows to the tympanic membrane
This focuses the noise and increases the pressure on the tympanic membrane

Question 5

Is the tympanic cavity fluid-filled or air-filled?

Answer 5

Air-filled

Question 6

State 2 ways in which the ossicles increase the pressure of vibration of the tympanic membrane.

Answer 6

Focussing the vibrations from the large surface area of the tympanic membrane to the small surface area of the oval window – this decrease in surface area means that the pressure is increased
The incus has a flexible joint with the stapes, such that the ossicles use leverage to increase the force on the oval window
This amplifies the sound by 30 dB

Question 7

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

Answer 7

The cochlea contains fluid, in which you are trying to induce a pressurewave
If the tympanic membrane was continuous with the cochlea, you would go straight from air to fluid and 99% 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 allowed by the ossicles 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?

Answer 8

Tensor Tympani

Stapedius

Question 9

What is the name given to this reflex?

Answer 9

Auditory reflex

Question 10

What is the latency period of this 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 three compartments of the inner ear?

Answer 14

Scala Vestibuli
Scala Media
Scala Tympani

Question 15

Which types of fluid do each compartment contain?

Answer 15

Scala Vestibuli + Scala Tympani = perilymph

Scala Media = endolymph

Question 16

What structure connects the two perilymph compartments?

Answer 16

Helicotrema

Question 17

Describe how the cochlea functions.

Answer 17

The vibration of the tympanic membrane is conducted and amplified to a vibration of the oval window by the footplate of the stapes.
This vibration induces a pressure wave in the perilymph in the scala vestibuli.
This vibrates the scala media leading to vibration of the basilar membrane.
The round window vibrates as well to equalise the pressure in the cochlea.

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

The 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 and beneath the tectorial membrane

Question 21

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

Answer 21

Inner and outer hair cells

Question 22

Describe the features and function of inner hair cells.

Answer 22

Found on their own
Not in contact with the tectorial membrane
Send impulses to the brain
They have stereocilia that move in response to the movement of endolymph in the scala media
Roughly 3500 in the body

Question 23

Describe the features and function of outer hair cells.

Answer 23

Found in groups of three
They are in contact with the tectorial membrane
They receive input from the brain
Electromotile so can expand and contract to amplify the amount of vibration (this is the basis of the cochlear amplifier)
Damage can result in sensorineural hearing loss
Roughly 20,000 in the body

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?

Answer 26

Tip links

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 the 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

Describe the difference in K+ and Na+ concentration in the different compartments of the cochlea.

Answer 30

Scala Media = High K+ and Low Na+
Scala Tympani = High Na+ and Low K+
NOTE: stria vascularis maintains this concentration

Question 31

Describe the auditory pathway from the cochlea to the primary auditory cortex.

Answer 31

Spiral ganglion -> cochlear nuclei -> superior olive -> inferior colliculus -> medial geniculate nucleus -> primary 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 (they travel via the internal capsule)

Question 39

How do you localise short sound burst?

Answer 39

Interaural time delay

Question 40

How do you localise continuous sound?

Answer 40

Interaural intensity difference

Question 41

What is conductive hearing loss?

Answer 41

When diseases of the middle ear damage the ossicles or stiffen theirjoints so that the amplification system is eliminated – results in conductive hearing loss

Question 42

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

Answer 42

When the cochlea or cochlear nerve get damaged, the signal transmitted to the primary auditory cortex is reduced or lost
It can be caused by acoustic schwannoma (tumour of the cochlear nerve) or cerebellar tumours expanding and putting pressure on thecochlear nerve

Question 43

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

Answer 43

Presbyacusis