Mechanisms and Pathologies of Hearing

Question 1

What can cause a conductive hearing loss?

Answer 1

Otosclerosis
Otitis media or glue ear 
Blockage in external auditory meatus 
Ruptured tympanic membrane
Eustachian tube dysfunction

Question 2

What is a sensorineural hearing loss?

Answer 2

When there is damage to the cochlea, cochlear nerve or the central auditory pathway

Question 3

What can cause sensorineural hearing loss?

Answer 3

Damage to hair cells via ototoxic drugs or excessive noise
Spiral ganglion damage such as acoustic neuroma
Tinnitus
Auditory neuropathy

Question 4

What is otosclerosis?

Answer 4

A bony outgrowth of the stapes which impedes movement against the oval window

Question 5

How does otitis media cause a conductive hearing loss?

Answer 5

Fluid accumulation and pressure changes in the middle ear, impeding auditory ossicles

Question 6

Which is rinne’s test?

Answer 6

When you place the tuning fork on the mastoid process then by the ear

Question 7

Which test is weber’s test?

Answer 7

When you place the tuning fork on the forehead

Question 8

Rinne’s test: bone > air right ear
Weber’s: lateralises to right ear

What is the diagnosis?

Answer 8

Conductive hearing loss in right ear

Question 9

Rinne’s: bone > air (left ear)
Weber’s: lateralises to right ear

What is the diagnosis?

Answer 9

Sensorineural deafness in left ear

Question 10

Rinne’s: air > bone both ears
Weber’s: lateralises to left ear

What is the diagnosis?

Answer 10

Sensorineural hearing loss in right ear

Question 11

If Weber’s lateralises to the left ear, what are the two possible diagnoses?

Answer 11

Conductive hearing loss in left ear

Sensorineural hearing loss in right ear

Question 12

If bone is louder than air in a Rinne’s in the left ear, what are the two possible diagnoses?

Answer 12

Conductive hearing loss in left ear

Complete sensorineural deafness in left ear (because sound is conducted by bone to the other ear)

Question 13

What is conductive hearing loss?

Answer 13

Where there is a problem with the transmission of sound from the outer to the inner ear

Question 14

What is sound?

Answer 14

A compressed airwave, travels at 343 m/s

Question 15

What is frequency measured in?

Answer 15

Cycles per second (Hz)

Question 16

What is magnitude measures as?

Answer 16

Intensity of the sound in decibels

Question 17

What attaches the stapes to the oval window?

Answer 17

The annular ligament

Question 18

What does the middle ear do?

Answer 18

Allows conversion of sound waves in the air to the fluid of the inner ear

Question 19

How is the pressure transmitted to the oval window amplified?

Answer 19

Because the area of the tympanic membrane is greater than that of the oval window
Mechanical efficiency of the ossicles acting as levers

Question 20

What does the inner ear consist of?

Answer 20

The bony labyrinth
The membranous labyrinth
The organ of Conti

Question 21

In which bone is the bony labyrinth found?

Answer 21

The petrous part of the temporal bone

Question 22

Which parts does the bony labyrinth of the inner ear make up?

Answer 22

The vestibule
Three semicircular canals
Cochlea

Question 23

Which part of the inner ear is responsible for hearing in response to vibrations?

Answer 23

The cochlea

Question 24

What do the cavities of the bony labyrinth contain?

Answer 24

Perilymph

Question 25

What is the cochlear canal divided into?

Answer 25

Scala vestibule | Scala tympani

Question 26

Where do the vibrations travel in the inner ear?

Answer 26

Oval window - scala vestibule - out via the round window

Question 27

What lies within the cochlea which is part of the membranous labyrinth?

Answer 27

The scala media/cochlear duct

Question 28

What is the cochlear duct filled with and what is it bound by?

Answer 28

Endolymph - high conc of K+ and low conc of Na+ Vestibular/Reissner's membrane and the basilar membrane

Question 29

Where is the organ of Conti?

Answer 29

On the basilar membrane of the cochlear duct

Question 30

Function of the inner hair cells?

Answer 30

Sense sound - move in response to endolymph

Question 31

Function of the outer hair cells?

Answer 31

Amplify sound

Question 32

Where are the inner and outer hair cells found?

Answer 32

Both in the organ of Conti Outer hair cells are embedded in the tectorial membrane which runs the length of the organ of Conti

Question 33

Where do signals produced by the hair cells travel?

Answer 33

To the spiral/cochlear ganglion which are bipolar neurones, forming at the base of the hair cell Theses nerve endings form the cochlear division of CN VIII

Question 34

How do hair cells move?

Answer 34

Compression of perilymph in scala vestibule and tympani, producing oscillatory movements in the basilar membrane Movement of the membrane causes movement in tips of stereocilia - inner hair cells relative to endolymph - outer hair cells relative to tectorial membrane

Question 35

How does movement of the stereocilia generate a signal?

Answer 35

Mechanical displacement causes influx of K+ through their membrane This depolarises the hair cell Causes influx of Ca2+ through VGCC Intracellular rise in [Ca] causing release of neurotransmitter in the spiral ganglion cells The action potential then propagates along the nerve fibres of the CN VIII

Question 36

What is the tonotopic distribution of responding receptors?

Answer 36

Hair cells located at the base of the basilar membrane respond to hi frequencies Those at the apical aspect of the membrane respond to low frequencies

Question 37

Where does the central auditory pathway begin?

Answer 37

With bipolar neurones in the vestibulocochlear nerve

Question 38

Where does the vestibulocochlear nerve travel?

Answer 38

Through the internal acoustic meatus, into the posterior cranial fossa where it divides into the vestibular and cochlear divisions at the level of the brainstem to rostral medulla

Question 39

Where do bipolar neurones synapse onto second order neurones?

Answer 39

In the cochlear nuclei of the medulla | Then project in a tonotopic manner

Question 40

Where do the second order neurones travel?

Answer 40

Some synapse in the ipsilateral or contralateral superior olivary complex Others pass contralaterally and synapse directly in the inferior colliculus

Question 41

What does the superior olivary nucleus allow?

Answer 41

Localisation of sound in acoustic space | -discriminate differences in time of arrival or intensity of sound to each ear

Question 42

What do neurones passing from the superior olivary nucleus to the inferior colliculus pass through?

Answer 42

The lateral lemniscus

Question 43

Where do axons go from the inferior colliculus?

Answer 43

Medial geniculate nucleus | Then projected to the auditory cortex (Broadman's area in the temporal lobe)

Question 44

Summary of the central auditory pathway?

Answer 44

``` Cochlea Spiral ganglion cells Cochlear nucleus Superior olivary complex Inferior folliculus Medial geniculate nucleus Auditory complex ```