physiology of hearing

Question 1

Pinnae

Answer 1

Outside of ear
Help to detect where sound is coming from
Mammals have good hearing as pinnae allow us to focus on the sound

Question 2

Auditory canal

Answer 2

There to protect the delicate sections of your inner ear
Six cubic centimetre cavity that resonates at 3kHz

Question 3

Middle ear ossicles

Answer 3

Mechanical system for taking the weak waves and turning them into forceful waves to affect the fluid in the ear
Large area making large movements into a small area making small movements
Evolution of the free bone middle ear allowed mammals to hear the super high frequencies

Question 4

Ossicular mass and middle ear volume determine the frequency limits of hearing

Answer 4

The bigger it is the easier sound can go through the middle ear
The smaller the ossicles are the higher frequency you can hear
The larger the animal the more sensitive to lower frequencies are, the smaller the animal the is the less sensitive to lower frequencies you are

Question 5

Cochlear

Answer 5

Sound pressure waves go up and down the cochlear
Pressure wave has to go somewhere
Auditory nerve are arranged following the curves of the cochlear
Goes up through scala vestibuli and down through scala tympani

Question 6

Basilar membrane

Answer 6

Starts the process of hearing
Narrow light and stiff at the bottom
Wide heavy and floppy at the top
Vibrates in sympathy with sounds of different frequencies in the air

Question 7

Perilymph

Answer 7

One type of fluid in inner ear
Located in scala vestibuli and scala tympani

Question 8

Endolymph

Answer 8

One type of fluid in the ear
Located in scala media
Different to perilymph because of how many potassium ions are being pumped in

Question 9

Organ of corti

Answer 9

Afferent nerves take external sensory experiences and bring them in
Efferent nerves work with the cochlear, sending signals from the brain to the cochlear to let brain control it

Question 10

Stereocilium

Answer 10

Detect vibrations
Tip links connect each stereocilium in the bundle to the next
Pull open ion channels
llows auditory system to do really precise timings
Movement of the ions helps the scala vestibuli and scala typmani
Change length in response to voltage
Tuned to particular frequencies and will move differently to different sounds

Question 11

Amplification

Answer 11

Amplification from OHCs (outer hair cells) can be 60 Db for low level sounds but reduces with increasing sound level, explaining slow loudness growth
Positive feedback amplification diagram

Question 12

Auditory nerve

Answer 12

Has lots of different axons of the nerve fibres that are taking the information off to the brain
One nerve is only going to pick up information about certain frequencies, due to the outer hair cells being specialised to different frequencies
They can detect faint noises but if you increase the sound level then they will respond to a wider range of frequencies

Question 13

Passive tuning mechanism in auditory system

Answer 13

Not precise like the cochlear

Question 14

Active tuning mechanism in auditory system

Answer 14

Finely tuned

Question 15

Phase locking

Answer 15

Auditory nerve response corresponds to wavelength
Important for sound localisation and may be critical for pitch perception
Lots of nerve fibres to represent more cycles of the waveform

Question 16

Volley principle - Wever & Bray (1930)

Answer 16

Groups of neurons of the auditory system respond to a sound by firing action potentials slightly out of phase with one another so that when combined, a greater frequency of sound can be encoded and sent to the brain to be analysed
Fun colourful diagram.