6.1 Special Senses (Pt 2 The Ear)

Question 1

What are the two properties of sound waves?

What is the unit of measurement and the normal range of each

Answer 1

1) Frequency = distance in hertz, normal range 20-20,000 Hz 2.
2) Volume = pressure in decibels dB Conversations are ~60 dB

Question 2

At which dB does hearing become painful?

Answer 2

Painful at 120 dB

Question 3

What is Auditory transduction and describe how this occurs in the cochlea

Answer 3

Auditory transduction is the conversion of a sensory stimuli from one form to another

1) vibration of stapes at oval window→ vibrations of perilymph in scala vestibuli
2) Transmitted to endolymph in cochlear duct and spiral organ of Corti on basilar membrane
3) Hair cells stimulated→ impulses travel along CNVIII to brain

Question 4

How many and what is the function of the hair cells that allow auditory transduction in the organ of Corti?

Answer 4

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

Question 5

In what area (base/apex) of the cochlea and low vs high frequencies picked up?

How does this relate to the type of sound loss experienced with age?

Answer 5

High frequency picked up at the base of the cochlea
low frequency picked up at the apex of the cochlea

With old age hair cells degenerate at the base and this is why we get a high frequency loss

Question 6

What are the two auditory pathways? Briefly describe each and identify which is more common

Answer 6

1) Primary (lemniscal) pathway: main pathway in which auditory info reaches the primary auditory cortex located in the temporal lobe
2) Non-lemniscal pathway: mediating unconscious perception (eg. attention, emotional response, and auditory reflexes)

Question 7

Why does a supranuclear lesion (above ocularmotor nuclei) not lead to hearing loss?

Answer 7

Because some fibres from each auditory pathway (lemniscal and non-lemniscal) cross over, so info from both ears travels bilaterally

This is why we do not suffer a hearing loss with a stroke

Question 8

Describe the primary (lemniscal) pathway of the ear (7 steps)

Answer 8

1. Cochlea
2. CN8
3. Pons (cochlear nerve nucleus here)
4. Olive
5. Inferior Colliculus (@ midbrain)
6. Medial Geniculate Nucleus (@ thalamus)
7. Primary Auditory Cortex (in temporal lobe)

Question 9

What is an otoscopy?

How does examination method differ in adults vs in children <2?

Answer 9

Use shortest and largest speculum. Hold otoscope like a pen with the handle upwards

In adults: pull the helix up and back to straighten the ear canal

In children <2: pull earlobe down

Question 10

Describe how you would perform Rinne’s test, what is the normal finding?

Answer 10

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

Question 11

Describe how you would perform Weber’s test, what is the normal finding?

Answer 11

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

Question 12

What is pure tone audiometry and what does it test?

Answer 12

It is a quantitative hearing assessment to show the nature and degree of hearing loss

It Tests air and bone conduction and graphically shows how loud (dB) a particular frequency (Hz) must be played to be heard

Graph = audiogram

Question 13

How do you read an audiogram?

Answer 13

loudness in dB (down the side) against frequency in Hz (across the top)

Right is round and red and left is crosses (to remember which ear)

Question 14

How do we know each of the following audigrams indicate each specific hearing loss?

Answer 14

Noise induced: shows a dip at 4-6 kHZ (typical feature) usually both side

Sensorineural: left side is abnormal (the little square marks are the bone conduction marks) as bone and air conduction are SAME level it is a unilateral sensorineural hearing loss

Congenital: cookie bite image is typical

Presbyacusis: hearing worsens with higher frequency

Conductive loss: bone conduction is better than air therefore image shows conductive loss

Question 15

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

Answer 15

a) 0-25 dB
b) 26-40 dB
c) 41-55 dB
d) 71-90 dB
e) >90 dB

Question 16

Where would a lesion be in the following types of hearing loss?

Conductive

Sensorineural

Mixed

Central

Answer 16

Conductive: lesions in the outer or middle ear

Sensorineural: lesions in the inner ear or auditory nerve

Mixed: combination of above

Central: lesion in the auditory pathway in the brain (rare)

Question 17

What is the difference between a hearing aid and a cochlear implant?

Answer 17

While a hearing aid can amplify sound, a cochlear implant transforms sound into electrical energy that can stimulate the auditory nerves in the inner ear

Question 18

Describe how a cochlear implant works

Answer 18

1) Sounds picked up on microphone which is on external ear piece
2) Speech processor digitizes sound into signals
3) Transmitting coil sends coded signals as radio waves to the cochlear implant under the skin
4) 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
5) Electrodes along the array stimulate the remaining auditory nerve fibres in the cochlea
6) Resulting electrical sound info is sent through the auditory system to the brain!