Neuro - Auditory System

Question 1

How many sections is the ear generally divided into?

Answer 1

→ outer
→ middle
→ inner

Question 2

Where is the auditory organ located?

Answer 2

embedded in the petrous portion of the temporal bone (hardest bone in body)

Question 3

What are the functions of the outer ear?

Answer 3

→ captures sound and focuses it in the tympanic membrane
→ amplify some frequencies by resonance in the canal
→ protect ear from external threats (done by hair and wax)

Question 4

What are the functions of the middle ear?

Answer 4

amplification by:
→ focusing vibrations from large surface area (tympanic membrane) to smaller surface area (oval window). The change in surface area means the pressure is increased.
→ Using leverage from the incus-stapes joint to increase the force on the oval window

Question 5

What is the hearing part of the inner ear?

Answer 5

cochlea

Question 6

What is the function of the inner ear?

Answer 6

→ transduce vibration into nervous impulses

→ produces a frequency (or pitch) and intensity (or loudness) analysis of sound

Question 7

What are the 3 compartments of the cochlea when it’s uncoiled?

Answer 7

→ scala vestibuli
→ scala media
→ scala tympani

Question 8

What are the scala vestibuli and scala tympani?

Answer 8

bone structures, contain perilymph (high in sodium)

Question 9

What is the scala media?

Answer 9

→ membraneous structure that contains endolymph (high in potassium)
→ contains the hearing organ / Organ of Corti
→ sandwiched between scala vestibuli and tympani

Question 10

What membrane contains the organ of Corti?

Answer 10

basilar membrane

Question 11

How is the basilar membrane arranged?

Answer 11

→ arranged tonotopically (thicker in one end, thinner the other) like a xylophone
→ base = narrow + tight
→ apex = wide + loose
→ sensitive to different frequencies at different points along length

Question 12

What are the two types of hair cells in the Organ of Corti? How are they arranged?

Answer 12

→ inner hair cells, arranged in 1 column

→ outer hair cells, arranged in 3 columns

Question 13

What is the purpose of the tectorial membrane in the Organ of Corti?

Answer 13

→ located above the hair cells
→ always in constant contact w OHCs, which assist in contact with IHCs
→ allows for hair deflection
→ this depolarises the cells

Question 14

What are the functions of IHCs?

Answer 14

→ carries 95% of afferent info of the auditory nerve

→ transduces sound into nerve impulses

Question 15

What are the functions of OHCs?

Answer 15

→ carries 95% of efferent info of the auditory nerve

→ modulates sensitivity of the response

Question 16

What are the hairs of the hair cells called?

Answer 16

stereocilia

Question 17

What does deflection of the stereocilia do?

Answer 17

→ mechanically opens the potassium open channels
→ ionic interchange = depolarisation of cell
→ neurotransmitter is liberated

Question 18

How does amplitude of sound affect deflection?

Answer 18

higher amplitudes (louder sounds) causes greater deflection of stereocilia, more hair cells involved, etc.

Question 19

What does hyper-polarisation of hair cells cause?

Answer 19

closes potassium channels

Question 20

What is the auditory pathway from cochlea to cerebral hemispheres?

Answer 20

→ spiral ganglions form each cochlea project via auditory vestibular nerve (VIII) to ipsilateral cochlear nuclei (monoaural neurones)
→ auditory info crosses at the superior olive level in brainstem
→ after this point, all connections are bilateral
→ goes through inferior colliculus and medial geniculate body in thalamus
→ ends in auditory cortex

Question 21

What happens if a sound is too soft to cause deflection?

Answer 21

OHCs contract to bring the tympanic membrane closer to the stereocilia of the IHCs to cause deflection so sound can be heard

Question 22

What happens if a sound is too loud?

Answer 22

→ OHCs can elongate
→ pushes tympanic membrane away from stereocilia of IHCs
→ less deflection = less loud sound transduced

Question 23

How is hearing arranged in the auditory cortex?

Answer 23

→ tonotopically organised (like a xylophone)

→ low freq to high freq anterior-posteriorly in the brain

Question 24

What is frequency / pitch? What is it measured in?

Answer 24

→ cycles per second, perceived tone

→ measured in Hertz

Question 25

What is amplitude / loudness? What is it measured in?

Answer 25

→ sound pressure → subjective attribute correlated with physical strength → decibels

Question 26

What is the human range of hearing for frequency?

Answer 26

20Hz - 20,000 Hz

Question 27

What is the human range of hearing for amplitude?

Answer 27

0 dB - 120 dB

Question 28

Why is the decibel scale useful?

Answer 28

→ log scale, so range of sensitivity is high → allows compression of scale onto a graph → reflects on idea that many physiological processes are on-linear

Question 29

How does hearing acuity change with age?

Answer 29

decreases with age, especially high frequencies

Question 30

How are medium + low frequencies affected through life?

Answer 30

progression of hearing loss

Question 31

What are the aims of a hearing assessment?

Answer 31

→ is there hearing loss? → what is the degree of hearing loss, if yes? → what is the type of hearing loss, if yes?

Question 32

What are the procedures used to test hearing during a hearing assessment?

Answer 32

- Tuning fork - Audiometry - Central processing assessment - Tympanometry - Otoacustic Emission - Electrocochleography - Evoked potentials

Question 33

How and why is the tuning fork used?

Answer 33

→ Weber test or Rinne test → Used to establish the probable presence or absence of a hearing loss with a significant conductive component → provide early and general information, when audiometry is not available or possible

Question 34

What is PTA?

Answer 34

→ pure tone audiometry | → science of measuring hearing acuity for variations in sound intensity and frequency

Question 35

What is a audiogram?

Answer 35

→ where hearing thresholds are plotted to define if there is a hearing loss or not → normal hearing threshold is located between 0-120dB

Question 36

What is an audiometer?

Answer 36

device used to produce sound of varying intensity and frequency

Question 37

What is a CPA?

Answer 37

→ central processing assessment → assessment of hearing abilities other than detection → verbal + non-verbal tests → examples: sound localisations, filtered speech, speech in noise

Question 38

What is the Weber test?

Answer 38

vibrate tuning fork at the top of the head to assess whether hearing loss (if any) is symmetrical

Question 39

What is the Rinne test?

Answer 39

compares direct stimulation of outer + middle ear with direct stimulation of the inner ear

Question 40

When is the tuning fork method used?

Answer 40

in GPs, usually when there's no alternative method available at the moment

Question 41

What is tympanometry?

Answer 41

examination used to test the condition of the middle ear + mobility of the eardrum (tympanic membrane) + the conduction bones by creating variations of air pressure in the ear canal

Question 42

What are OAEs? Why are they tested?

Answer 42

→ normal cochlea produces low-intensity sounds called OAEs → sounds are produced specifically by OHCs as they expand and contract → often part of the newborn hearing screening and hearing loss monitoring.

Question 43

What are auditory evoked potentials? What are 3 most common types that clinics look for?

Answer 43

action potentials evoked by auditory stimuli: → electrocochleography → ABR (auditory brainstem response) → late response

Question 44

What is electrocochleagraphy?

Answer 44

→ 0.2-4.0 ms → electrical activity from the cochlea and eighth nerve → evoked by clicks or tone burst

Question 45

What is ABR (auditory brainstem response)?

Answer 45

→ 1.5-10.0 ms → electrical activity from the eighth nerve and brainstem nuclei and tracts (auditory pathway) → ABR is more commonly used in clinic → evoked by clicks → does not require attention from patient

Question 46

What are late responses?

Answer 46

→ 80-500+ ms → electrical activity from the primary auditory and association cortex → evoked by tone burst and oddball paradigm

Question 47

What do alterations in latency of waves show?

Answer 47

can point to the location of the deficit

Question 48

What are cortical potentials useful?

Answer 48

useful in investigations of neurological conditions or processing problems

Question 49

What are the 3 types of hearing loss?

Answer 49

→ conductive hearing loss → sensorineural hearing loss → mixed hearing loss

Question 50

What is conductive hearing loss?

Answer 50

problem is in outer + middle ear

Question 51

What is sensorineural hearing loss?

Answer 51

problem is in inner ear or auditory nerve

Question 52

What is mixed hearing loss?

Answer 52

→ conduction + transduction of sound are affected | → more than one part of the ear is affected

Question 53

What are the different degrees of hearing loss?

Answer 53

``` → normal → mild → moderate → severe → profound ```

Question 54

What are some of the causes of conductive hearing loss affecting the outer ear?

Answer 54

→ wax | → foreign body

Question 55

What are some of the causes of conductive hearing loss affecting the middle ear?

Answer 55

→ otitis | → otosclerosis

Question 56

What are some of the causes of sensorineural hearing loss affecting the inner ear?

Answer 56

→ presbycusis | → ototoxicity

Question 57

What are some of the causes of sensorineural hearing loss affecting the nerve?

Answer 57

8th cranial nerve tumour

Question 58

What are the different treatments for hearing loss?

Answer 58

→ underlying cause → hearing aids → cochlear implants → brainstem implants

Question 59

What is the main purpose of hearing aids?

Answer 59

amplifies sounds but doesn't replace any specific structure

Question 60

What is the main purpose of cochlear implants?

Answer 60

replaces functions of hair cells by receiving sound, analysing it + transforming it into electrical signals + sending an electric impulse directly to the auditory nerve

Question 61

What does a cochlear implant need in order to function?

Answer 61

needs a functional auditory nerve

Question 62

What is the main purpose of a brainstem implant?

Answer 62

→ when the auditory nerves are the affected structures, the electrical signals can be sent to a set of electrodes directly into the brainstem → very risky, advised for people w bilateral important auditory nerve damage