Auditory system

Question 1

What is the function of a vestibular organ?

Answer 1

Capture low frequency motion (movement)

Question 2

What is the function of a hearing organ?

Answer 2

Capture high frequency motion (sound)

Question 3

What is the primitive mechanism of vestibular organs?

Answer 3

Statocyst - crystallised calcium ball moves freely across cells with hairs during movement which is transduced to an electrical signal

Question 4

What are the evolved vestibular and hearing organs present in humans?

Answer 4

vestib: Utriculus and Sacculus,
audio: Cochlea and Canals

Question 5

What relative frequencies do vestibular and hearing organs detect?

Answer 5

Vestibular - low frequency (movement), Hearing - high frequency (sound)

Question 6

What is frequency?

Answer 6

Cycles per second
pitch (Hz)

Question 7

What is amplitude?

Answer 7

Sound pressure, associated with physical strength
volume (dB)

Question 8

Human range of hearing

Answer 8

20 - 20k Hz
0 - 120 dB

Question 9

What are the structures in the outer ear?

Answer 9

Pinna,
External Acoustic Meatus,
Tympanic Membrane (eardrum)

Question 10

What are the three functions of the outer ear?

Answer 10

Capture sound and focus to tympanic membrane Amplification of sound (by 10dB)
Protection of ear from external threats

Question 11

What is the bony structure in the middle ear and what is its functions?

Answer 11

Ossicles - vibrate to create mechanical amplification of sound by 30dB

Question 12

What are the muscular structures in the middle ear and what are their functions?

Answer 12

Tensor tympani muscle, Stapedius muscle
- protection by reducing sound that reaches the middle ear during loud noises

Question 13

What is the main structure in the inner ear and what is its function?

Answer 13

Cochlea, transduce vibration signals into nervous impulses, capturing frequency and amplitude

Question 14

What are the three compartments in the cochlea, and what do they contain?

Answer 14

Scala vestibuli
Scala tympani
scala media

Question 15

What are the bony structures in the cochlea

Answer 15

Scala vestibuli (vestibular side)
scala tympani (basilar side)
- contain perilymph (high in Na+)

Question 16

What is the middle membranous layer of the cochlea

Answer 16

Scala media - contains endolymph (K+),
contains the Organ of Corti (hearing organ, has hairs)

Question 17

What are the three structures in the Organ of Corti?

Answer 17

Basilar membrane, Hair Cells, Tectorial Membrane

Question 18

How is the basilar membrane arranged?

Answer 18

Tonotopically (like a xylophone) -
narrow base is for high frequencies, wider apex is for lower frequencies

Question 19

What type of hair cells does the Organ of Corti contain and how are they arranged?

Answer 19

Inner hair cells (in one line) and Outer hair cells (form three lines)

Question 20

What is the function of the IHC?

Answer 20

Inner hair cells - carry 95% of afferent information, transduction of sound into nerve impulses

Question 21

What is the function of the OHC?

Answer 21

Outer hair cells - carry 95% of efferent information, modulation of sensitivity of response

Question 22

What is the role of the tectorial membrane?

Answer 22

Above the hair cells, allowing hair deflection which in turn will depolarise the cell

Question 23

What are the hair cells also known as and what is the largest one called?

Answer 23

Stereocilia // Kinocilia

Question 24

How does transduction occur across the IHC?

Answer 24

Deflection of stereocilia towards kinocilia opens K+ ion channels,
cell depolarisation
Ca2+ channels open, stimulates excitatory glutamate neurotransmitter release.

Deflection of stereocilia away from kinocilia causes hyperpolarisation and inhibits nerve discharge

Question 25

Effect of amplitude on stereocilia

Answer 25

High amplitudes (volume) will cause greater deflection of stereocilia and k+ channel opening leading to greater neural signal

Question 26

Effect of frequency on stereocilia

Answer 26

Has no effect on movement of stereocilia

Question 27

Main points of transduction

Answer 27

Depolarisation - opens k+ channels Hyperpolarisation - closes k+ channels

Question 28

How does auditory information travel from the cochlea to the cerebral hemisphere?

Answer 28

Stereocilia -> vestibulocochlear nerve's spiral ganglions ipsilaterally to the cochlear nuclei (monoaural) in the brainstem. bilateral superior olives inferior colliculus. medial geniculate body in the thalamus, cerebral hemisphere

Question 29

What are the three types of anatomical hearing loss?

Answer 29

Conductive (outer or middle ear), Sensorineural (cochlear or auditory nerve - 90% of cases), Central Hearing Loss (rare, brainstem)

Question 30

What is conductive hearing loss

Answer 30

Affects outer or middle ear

Question 31

What is sensorineural hearing loss

Answer 31

affects the cochlear or auditory nerve

Question 32

What is central hearing loss

Answer 32

affects the brain and brainstem

Question 33

What are the two types of hearing loss with regards to timing?

Answer 33

Sudden hearing loss (minutes and days), Progressive hearing loss (months to years)

Question 34

What are four causes of conductive hearing loss?

Answer 34

Outer ear - cerumen impaction (wax), foreign body // Middle ear - otitis (inflammation causes bubbles of liquid to be present in middle ear) , Otosclerosis (ossicles fuse together with age and do not vibrate properly) abnormal bone growth

Question 35

What are four causes of sensorineural hearing loss?

Answer 35

Inner ear - noise, presbycusis (old age), ototoxicity (chemotherapy, antibiotics - gentamicin) nerve - vestibular schwannoma (acoustic neuroma) tumour pushes on the 8th nerve causing unilateral hearing loss

Question 36

What are two quick bedside tests for clinical assessment of hearing loss?

Answer 36

Whispering numbers in ear and rubbing fingers in other ear - can they hear, Tuning fork test

Question 37

What are the tuning fork tests and what do they show?

Answer 37

Weber test - fork on top of head, tests both ears hearing Rinne test - on mastoid process behind ear, compares left and right hearing

Question 38

How does audiometry work?

Answer 38

Measure the patients hearing threshold - the lowest amplitude required to hear different frequencies

Question 39

What lowest levels of audiometry is normal?

Answer 39

Lowest - 10-20dB

Question 40

How can you observe conductive hearing loss on an audiometry graph?

Answer 40

Two different graphs for bone and air Bone conduction is normal (showing there is no problems with auditory nerves) but air conduction is impaired (showing there is a problem with the outer and middle ear)

Question 41

How can you observe sensorineural hearing loss on an audiometry graph?

Answer 41

Both bone and air hearing is impacted

Question 42

How can you do newborn hearing screening?

Answer 42

Otoacoustic emissions are low-intensity sounds produced by outer hair cells as they expand and contract.

Question 43

What are the two main treatments for hearing loss?

Answer 43

Treatment of the underlying conditions (wax buildup or tumour) or hearing aids

Question 44

What are two rare treatments for hearing loss?

Answer 44

Cochlear implants and brainstem implants