21 - Hearing

Question 1

What are the two functions of the auditory system?

Answer 1

• Hearing: Distinguishing between sounds and localisation

- Language: Production and comprehension

Question 2

What is the function of the outer ear?

Answer 2

• Detects air vibration and protects, localises and amplifies

Question 3

What is the function of the middle ear?

Answer 3

Detects mechanical vibrations, has functions in impedance matching (matching vibrations in air to the vibrations in the fluid in the cochlear), pressure equalisation (via eustachian tube) and inner ear stimulation (via stapes)

Question 4

What is the function of the inner ear?

Answer 4

Detects mechanical, hydrodynamic and electrochemical signals
Functions in sound filtering and signal transduction
Maintains balance by detecting position and motion

Question 5

What are the cartilages that the outer ear is made up of?

Answer 5

Helix, antihelix, tragus, anti-tragus, superior and inferior crus

Question 6

What are the names of the three bones in the middle ear?

Answer 6

Malleus, incus and stapes

Question 7

What are the three canals in the cochlea?

Answer 7

Cochlear duct, scala vestibuli and scala tympani

Question 8

Where is the organ of corti found?

Answer 8

In the cochlea - between the scala tympani and vestibuli

It is the receptor organ for hearing

Question 9

How many rows of outer and inner hair cells does the organ of corti have on the basilar membrane?

Answer 9

3 rows of outer hair cells

1 row of inner hair cells

Question 10

What is the difference in the roles of the outer and inner hair cells?

Answer 10

Inner hair cells - Auditory discrimination, cilia is not embedded in tectorial membrane
Outer hair cells - Role in frequency tuning anf amplification of sound, cilia is embedded in the tectorial membrane

Question 11

How is sound loudness created?

Answer 11

Intensity of vibrations

Greater the amplitude = more basilar membrane will vibrate = stronger signals to the brain = sound perceived as louder

Question 12

What are the dB SPL of a whisper, quiet conversation, normal conversation?

Answer 12

Whisper - 40dB
Quiet conversation - 60dB
Normal conversation - 70dB

Question 13

Draw a diagram of the auditory pathway

Answer 13

• See google docs

Question 14

What is impedance matching?

Answer 14

Allows for the same signal to be transferred by the external, middle ear and cochlea (external and middle are filled with air but the cochlea is filled with fluid so they have different resistances)
The sizes of the ossicles ensure the movement ration causes the same amount of vibration to be transferred from the air to the fluid in the cochlea
1) the stapes with transfer more vibration than the malleus - fluid has more resistance than air
2) Tympanic membrane is larger than the oval window - small oval window means more vibration is transferred to the cochlea that what was transferred to the tympanic membrane
^^ combine to produce impedance matching

Question 15

What are the functions of the acoustic reflexes?

Answer 15

To prevent damage

To distinguish between sounds and background noise

Question 16

What is the attenuation reflex?

Answer 16

Is activated by own voice/lound sounds - contraction of muscles such as stapedius - dampen transmission from middle to inner ear - 50-100ms delay so doesn’t offer protection from sudden loud sounds - if there is damage you could get hyperacusis (increased sensitivity to loud sounds)

Question 17

What is the startle reflex?

Answer 17

Defence against sudden or threatening stimuli - facial nerve and reticular formation - protect the back of the neck and the eyes - less than 10ms latency period

Question 18

What is the difference between the dorsal and ventral cochlear nucleus?

Answer 18

Ventral cochlear nucleus - fast and precise, projects to the superior olivary nucleus, encodes intensity by satellate cells and encodes timing by bushy cells
Dorsal cochlear nucleus - complex processes, projects to the lateral lemniscus, encodes the quality of sound, analyses pitch by detecting minor frequency differences

Question 19

Where does the vestibulocochlear nerve emerge at?

Answer 19

Pontomedullary junction

Question 20

What is the function of the superior olivary nucleus?

Answer 20

Helps to identify the source of the sound - uses interaural time differences

Question 21

What are interaural time differences and interaural level differences?

Answer 21

Interaural time differences = difference between the times sounds reach the 2 ears (more useful at low freq)
Interaural level differences = differences in loudness (more useful at high freq)

Question 22

What are the two deafness classifications and the difference between them?

Answer 22

• Conduction deafness = hearing loss due to sounds not being able to freely pass into the inner ear
  Caused by blockage (excess wax or fluid), anatomical abnormality of the outer ear, ear canal or middle ear, or a ruptured ear drum = sounds become quieter but not distorted
  Can be both temporary or permanent
• Sensorineural deafness = hearing loss due to damaged hair cells within the cochlea or the hearing nerve, normal process of ageing but may also occur in prolonged exposure to loud sounds, drugs, rubella, tumour
  Sounds become quieter and the quality of speech is also reduced
  Damage is often irreversible

Question 23

What is Rinne’s test?

Answer 23

Vibrating tuning fork placed on the mastoid process and then next to the ear canal
Compares air conduction to bone conduction
Normal = sound louder and longer by air conduction
Conduction deafness = bone conduction better than air conduction on affected side
Sensorineural deafness = air conduction better than bone conduction in affected ear with sound loudest in unaffected ear

Question 24

What is Weber’s test?

Answer 24

Tuning fork places in the middle of the forehead and is asked in which ear tone is heard
Normal response = sound heard equally on each side
Conduction deafness = sound is louder in the affected ear (vibrations will reach the cochlea by air and bone but are slightly out of phase and so will interfere with each other more in the sensitive ear and so the sound will seem louder)
Sensorineural deafness = sound is louder in unaffected ear
Cannot be interpreted directly as it only detects the relative difference between the two ears

Question 25

What is otitis media?

Answer 25

Inflammation of the middle ear caused by infection

Question 26

What is otosclerosis?

Answer 26

Progressive deafness due to overgrowth of bone near the middle ear - mainly affects stapes

Question 27

What is the difference between a schwannoma and meningioma?

Answer 27

Schwannoma - benign neoplasm arising from the myelin sheaths of cranial nerves - common in vestibular nerve - acoustic neuroma/vestibular schwannoma - unilateral hearing loss - tinnitus - disequilibrium
Meningioma - arises from the arachnoid layer of the meninges - can affect CN V,VII, VIII, IX, X and XII

Question 28

What happens if there is damage to Wernicke’s area?

Answer 28

Fluent but meaningless speech - impaired speech comprehension

Question 29

What happens if there is damage to Broca’s area?

Answer 29

Abbreviates, ungrammatical but meaningful speech - understanding impaired where syntax conveys meaning

Question 30

What happens if there is damage to the arcuate fasciculus?

Answer 30

Conduction aphasia - fluent speech production but poor speech repetition

Question 31

What happens if there is damage to the angular gyrus?

Answer 31

Alexia (cannot read) with agraphia (cannot write) but can comprehend speech and speak themselves