Special Senses: The Ear Flashcards
What are the two properties of sound waves? What is the unit of measurement and the normal range of each
- Frequency = distance in hertz, normal range 20-20,000 Hz
- Volume = pressure in decibels dB
Conversations are ~60 dB
At which dB does hearing become painful?
Sound becomes loud to the point of painful at 120 dB
How common is tinnitus in the UK? How many children are born with severe or profound hearing impairment?
Tinnitus: 1/10
Children born with severe or profound hearing impairment: 1/100
What does hearing loss predominantly increase with?
Age
What is Auditory transduction and where in the ear is it performed? Where does the ‘sound’ then travel?
Auditory transduction is the conversion of a sensory stimuli from one form to another by the organ of corti in the cochlear of the inner ear
Sound is then projected by the auditory pathway (Cn VIII) to the temporal lobe of the cortex
Describe how the structure of the basilar membrane (where the spiral organ of corti is) allows for auditory transduction?
There are 4 rows of hair cells
- 1 inner which provides most of the signal to CN VII
- 3 outer which modulates the response of the inner hair cells
What are the two auditory pathways? Briefly describe each and identify which is more commo
- Primary (lemniscal) pathway: the main pathway which auditory info reaches the primary auditory cortex
- Non-lemniscal pathway: mediates unconscious perception (i.e attention, emotional response and auditory reflexes)
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Why does a supranuclear lesion (above ocularmotor nuclei) not lead to hearing loss?
Because some fibres from each auditory pathway (lemniscal and non-lemniscal) cross over, so info from both ears travels bilaterally
Which preparations should you perform when about to do an otoscopy in adults vs in children <2?
In adults: pull the helix up and back to straighten the ear canal
In children <2: pull earlobe down
Describe how you would perform Rinne’s test, what is the normal finding?
Place fork at the external meatus and then the mastoid process and ask which is louder
*normal: should be louder at the external meatus as air conduction>bone conduction
Describe how you would perform Weber’s test, what is the normal finding?
Place tuning fork on the forehead in the midline and ask which ear has the loudest sound or if its heard loudest ‘centrally’ (i.e no difference)
*normal: loudest centrally
What is pure tone audiometry and what does it test?
It’s a quantitative hearing assessment that graphically shows the volume (dB)/y axis and particular frequency (Hz)/x axis of a noise that must be played to be heard - therefore it shows the nature and degree of hearing loss
Which type of hearing loss is the most rare?
Central: lesion in the auditory pathway in the brain
List the volume ranges for the following
a) normal hearing
b) mild hearing loss
c) moderate hearing loss
d) severe hearing loss
e) profound hearing loss
a) 0-25 dB
b) 26-40 dB
c) 41-55 dB
d) 71-90 dB
e) >90 dB
What is the difference between a hearing aid and a cochlear implant?
While a hearing aid can amplify sound, a cochlear implant transforms sound into electrical energy which can stimulate the auditory nerves in the inner ear
Describe how a cochlear implant works
- Sounds picked up on microphone which is on external ear piece
- Speech processor digitizes sound into signals
- Transmitting coil sends coded signals as radio waves to the cochlear implant under the skin
- The internal processor (placed in the mastoid bone behind the ear)/cochlear implant delivers electrical energy to an array of electrodes which have been inserted into the cochlea
- Electrodes along the array stimulate the remaining auditory nerve fibres in the cochlea
- Resulting electrical sound info is sent through the auditory system to the brain!
Why do tuning fork tests help to differentiate and why are they limiting?
They can differentiate between conductive and sensorineural hearing loss but only if there is a single type of hearing loss (conductive/sensorineural) present in one ear only
If lateralisation is heard in Weber’s test what does it mean in terms of a conductive/sensorineural deafness diagnosis?
Weber’s will be heard louder TOWARDS the side of conduction and AWAY from the side of sensorineural
Explain a positive and negative Rinne finding
Positive in normal/Sensorineural hearing as the AC>BC
Negative in conductive hearing as BC>AC in affected ear
Analyze the following images
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Which structures might be damaged in sensorineural hearing loss?
The cochlea or the acoustic nerve CN VIII
Describe what you would see in the audiogram of an individual with presbyacusis
Since it’s high frequency sensory hearing loss (SNHL) the low frequencies would be in normal range and the higher frequencies would need to be played much louder in order to be heard (decline in the slope)
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Describe what you would see in the audiogram of an individual with noise induced hearing loss
There’s a dip in the graph for both ears; a certain frequency must be played louder to be heard before coming back to normal
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Describe what you would see in the audiogram of an individual with congenital hearing loss
A “cookie bite” in the graph; so that certain mid-ranged frequencies must be played louder to be heard
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