Localising Sound

Question 1

What are the two mechanisms of localising sound

Answer 1

• interaural time difference
• interaural intensity difference

Question 2

What is interaural time difference

Answer 2

delay in arrival of sound wave at one ear relative to the next, at MSO (medial superior olive)

Question 3

What is interaural intensity difference

Answer 3

uses loudness perception from one of the two ears to determine location, at LSO (lateral superior olive)

Question 4

Funciton of the cortex

Answer 4

identify and process complex sounds

Question 5

Function of the medial geniculate

Answer 5

principle relay to cortex

Question 6

Function of the inferior colliculus

Answer 6

form full spatial map

Question 7

Shared function of the lateral and medial superior olive

Answer 7

locate sound sources in space

Question 8

Shared function of the dorsal cochlear nucleus, postero ventral cochlear nucleus, and antero ventral cochlear nucleus

Answer 8

start sound feature processing

Question 9

What is the cochlea

Answer 9

auditory nerve

Question 10

Acoustic stria

Answer 10

dorsal cochlear nuclei give rise to acoustic stria, which cross the midline and

Question 11

Function of medial superior olive

Answer 11

• computes sound arrival at the two ears
• ipsilateral ear earlier than contralateral
• generates an interaural time difference

Question 12

Mechanistic features of medial superior olive

Answer 12

• delay lines: coincidence detector
• timing code converted to place code for angular location
• tonotopic: matching across frequency bands

Question 13

Effect that ipsilateral anteroventral cochlear nucleus has on the lateral superior olive

Answer 13

excitatory input

Question 14

Contralateral anteroventral cochlear nucleus

Answer 14

• excites a neuron in the medial nucleus of the trapezoid body
• sends an inhibitory signal to the lateral superior olive neuron

Question 15

What happens if the aural signal is closer to the ipsilateral ear

Answer 15

• lateral superior olive will have a net depolarisation but will have net inhibition if the sound is closer to the other ear

Question 16

How are LSO neurons stimulated

Answer 16

• depolarising signal from ipsilateral ear
• hyperpolarising signal from contralateral ear
• each aural signal stimulates an LSO neuron from each hemisphere

Question 17

The balance between excitatory and inhibitory neurotransmission is important for…

Answer 17

determining the net excitation that is forwarded to the inf colliculus and the lat lemniscus

Question 18

Synaptic transmission at the Calyx of Held

Answer 18

• 600 conventional active zones where synaptic vesicles cluster facing the POSTSYNAPTIC DENSITY
• individual active zones are similar to those found in other brain synapses

Question 19

Importance of multiple sites of synaptic vesicle fusion

Answer 19

ensures fast, reliable synaptic transmission, such that incoming presynaptic APs reliably tirgger evoked APs even at high input frequencies