Hearing

Question 1

What is being detected when we perceive sound?

Answer 1

Wavelength: pitch

Amplitude: loudness

Waveform: tone/timbre

Question 2

Briefly describe how different elements of the anatomy of the auditory system are involved in sound perception?

Answer 2

Tympanic membrane moves ossicles

Ossicles move oval window

Cochlea tranforms physical motion of oval window into a neural response

Question 3

What is the function of the ossicles?

Answer 3

Matches the impedance of air to that of fluid in inner ear

Question 4

Describe the pressure that the ossicles must overcome?

Answer 4

Pressure 200 fold greater at tympanic membrane compared to inner ear

Size: tympanic memrane > oval window (20:1)

Lever action of ossicles: 1.3:1

Question 5

Describe the three chambers of the cochlea?

Answer 5

Scala vestibuli

Scala media

Scala tympani

Question 6

Where are the basilar membrane and tentorial membrane located?

Answer 6

Question 7

Describe the basilar membrane?

Answer 7

Wider at apex than base

Stiffer at base

Base responds to high frequencies, apex responds to low frequencies

(Like a flipper)

Question 8

What is the function of the basilar membrane?

Answer 8

Vibrates in response to sound waves

(certain areas vibrate depending on frequency)

Question 9

Describe the functional arrangement of the basilar membrane?

Answer 9

Tonotopic encoding of sound

Low frequencies at apex, high frequencies at base

Question 10

Where is the Organ of Corti situated?

Answer 10

In middle of cochlea

Sandwiched between basilar membrane and reticular lamina

Question 11

What does the Organ of Corti consist of?

Answer 11

Auditory receptors: inner and outer hair cells

Question 12

Where do the inner and outer hair cells sit in relation to other inner ear structures?

Answer 12

Sit on top of basilar membrane

Question 13

What is the function of the Organ of Corti?

Answer 13

Transduces soundwaves into neural signals

Question 14

Describe the hair cells of the inner ear?

Answer 14

Inner and outer

Each hair cell has about 100 stereocilia

Question 15

Describe the attachments of the sterocilia?

Answer 15

Hair cell to tectorial membrane

Question 16

Describe the role of the stereocilia?

Answer 16

bending of stereocilia causes neuronal signalling

Question 17

Describe how soundwaves initiate auditory transduction?

Answer 17

Movement causes basilar membrane to osciallte

Causes stereocilia to move

Shear force of stereocilia against tectorial membrane causes ion conductances

Question 18

What is the tallest stereocilium in a hair bundle called?

Answer 18

Kinocilium

Question 19

Describe how opening and closing of K channels within a hair cell is achieved?

Answer 19

K channels partially open

Deflection of hair bundle towards kinocilium causes more opening of channels > depolarisation

Hyperpolarisation > channel closure

Question 20

What is the effect of depolarisation in the hair bundles?

Answer 20

Depolarisation > opening of voltage-dependent Ca channels > glutamate release

Question 21

How does membrane potential differ according to different movements of hair bundles?

Answer 21

Asymmetric changes

Larger depolarisations than hyperpolarisations

Question 22

Describe the difference in K within the chambers of the cochlea?

Answer 22

Scala media: high K

Scala tympani: low K

Question 23

Describe the difference in function between the inner and outer hair cells?

Answer 23

Inner: for hearing

Outer: amplify movements of basilar membrane (depolarisation > contraction, hyperpolarisation > elongation)

Question 24

Describe the effect of loss of OHCs?

Answer 24

Basilar membrane movement is 100 fold less > loss of hearing

Question 25

What can cause loss of OHCs?

Answer 25

Antibiotics and other medications

Question 26

Describe the auditory pathway?

Answer 26

Question 27

How is sound from both ears integrated?

Answer 27

Extensive crossing across midline at brainstem level Information from cochlear nuclei on either side communicate at superior olivary complex

Question 28

Describe the superior olivary complex?

Answer 28

Conists of lateral and medial superior olives and trapezoid body These structures are crucial for working out where sound is coming from

Question 29

What are the functions of the medial and lateral superior olives?

Answer 29

MSO: localisation of sound by measuring time delay LSO: localisation of sound by sensing intensity differences

Question 30

Describe the duplex theory of sound localisation?

Answer 30

Provides an explanation for the ability of humans to localise sounds by time differences between the sounds reaching each ear and differences in sound level entering the ears. 1) Time that sound arrives at each ear 2) Interaural intensity differences

Question 31

Which sound frequencies are involved in each part of the duplex theory?

Answer 31

1) Time that sound arrives at each ear \> low frequencies 2) Interaural intensity difference \> high frequencies

Question 32

Describe how sound localisation is achieved using time differences?

Answer 32

Question 33

Describe how interaural intensity difference is used to localise sound?

Answer 33

Info carried down to cochlear nuclei and down to LSO Excitation to higher centres At same time, processes to contralteral trapezoid body \> communicates with inhibitory neuron in TB \> TB sends inhibitory singal to ipsilateral LSO At same time, same process is happening in opposite ear So, brain gets relative amount of excitation and inhibition from each ear to determine where sound is coming from

Question 34

Describe the orgnaisation of the auditory cortex?

Answer 34

Columnar organisation: cells in same column are tuned to the same frequency Also, alternating regions of input from both ears (excitatory from one ear, inhibitory from other)

Question 35

Describe the representation of sounds in the auditory cortex?

Answer 35

Asymmetric representation Speech sounds: left Environmental sounds: both hemispheres Music: right

Question 36

Describe the time frame within which sudden sensorineural hearing loss occurs?

Answer 36

Sudden loss of hearing of at least 30db within 3 hours to 3 days

Question 37

What are the causes of sudden hearing loss?

Answer 37

10-15% have known cause: Peripheral causes (meningitis, metastasis...) Central causes (MS) Cochlear causes (infection, autoimmune disease, trauma, vascular...)

Question 38

Which structures in the superior olive are importnat in which components of the duplex theory?

Answer 38

MSO - time differences LSO & TB - intensity differences