Hearing Lectures

Question 1

How do you hear sounds?

Answer 1

Read notes

Question 2

Frequency coding in auditory nerve

Answer 2

Place principle: cochlea is a filter and is tonotopically organised so that frequency is detected by spatial representation from base to apex. (specific place in cortex will receive that signal)

Volley principle: mainly for low frequencies are detected by temporal firing of nerve fibres in time to the frequency of the stimulus
-nerve fibre follows the frequency of sound - if the sterocilia move 100/second then will stimulate the nerve at this same rate - responds to the frequency of sound (code due to the pattern)

• fires at each apex of the wave
• cannot get this working at some frequencies so this is why we have the spacial representation

Question 3

Intensity coding

Answer 3

Intensity coding
-rate of firing of individual nerve fibers increases with sound intensity , number of fibers increase as energy spreads along the organ of corti

Question 4

What happens in the processing at each region

Answer 4

Choclea nucleous (medulla) -

• auditory nerve fibers terminate
• removes biological noise

Superior olivary complex (pons)

• major biaural hearing center
• important for determining interaural timing and intensity
• sound localization

Inferior colliculus (midbrain)

• major interactive center
• interaction with somatosensory and visual systems so enhance sound localisation

Medial geniculate body (thalamus) –> auditory cortex
-spacial localisation and speech recognition (through interactions with brocas area, and wernikes speech area)

Question 5

What is the choclea nucleus involved in?

Answer 5

ventral - projects directly to Superior olivary complex (sound localisation, measures inter-ear differences)

Dorsal - dominant part of human CN, projects directly to midbrain (important for speech)

Question 6

What examination methods are used for hearing?

Answer 6

– Otoscopy

-Clinical test of hearing(whisper test)

– Tuning fork testing (Weber and Rinne tests)

– Neurological examination: cranial nerves, special tests

-General exam

Air conduction Audiogram -

Tympanometry - asses ear drug motility (will tell you how much is getting through) , can also see if neural pathways are working , middle ear pressure

Question 7

Example of conductive hearing loss - and test results

Answer 7

congential vs aquired

inflammation - otitis media- due to eustachian tube build up - get glue ear, can also lead to mastoiditis

Otoscopy - will observe a fuzzy, non clear tympanic membrane due to blockage/infection in middle ear

Tympanometry - with glue ear will not get the mobility, so pressure does not fit withing normal range

Audiogram - air conductance poor, bone conductance good (gap between the two)

Conductive hearing loss - Weber test - to the same ear (and sensourinal - to opposite ear)

Rinne test - negative - if bone conduction is better than air conduction

Question 8

Sensorineural hearing loss

Answer 8

congenital vs aquired

weber test - to opposite ear
rinne test - positive (air condcution better than bone conduction)

-noise exposure, age

MRI scan

Question 9

How is an audiogram assessed

Answer 9

Assess sensitivity too sound, then plot sound level which person repsonds at each frequency - show how much sound you give before they can hear the sound
-good if in dark green bit

if it decreases at higher frequencies - usually for older people

Air conduction -use headphones - dont know if it is inner ear or middle ear (if this is bad then try bone conductance to see where problem is)
Bone conduction - use vibrations - if find that this is good - then inner ear is working okay but air conduction is no good - so problem with middle ear

Question 10

Tympanometry

Answer 10

• Assess mobility of ear drum
• can see how much tone is going into middle ear
• assesses ability of ear muscles

If glue ear - cannot get same pressure so will look different on test