Localising Sound Flashcards
What are the two mechanisms of localising sound
- interaural time difference
- interaural intensity difference
What is interaural time difference
delay in arrival of sound wave at one ear relative to the next, at MSO (medial superior olive)
What is interaural intensity difference
uses loudness perception from one of the two ears to determine location, at LSO (lateral superior olive)
Funciton of the cortex
identify and process complex sounds
Function of the medial geniculate
principle relay to cortex
Function of the inferior colliculus
form full spatial map
Shared function of the lateral and medial superior olive
locate sound sources in space
Shared function of the dorsal cochlear nucleus, postero ventral cochlear nucleus, and antero ventral cochlear nucleus
start sound feature processing
What is the cochlea
auditory nerve
Acoustic stria
dorsal cochlear nuclei give rise to acoustic stria, which cross the midline and
Function of medial superior olive
- computes sound arrival at the two ears
- ipsilateral ear earlier than contralateral
- generates an interaural time difference
Mechanistic features of medial superior olive
- delay lines: coincidence detector
- timing code converted to place code for angular location
- tonotopic: matching across frequency bands
Effect that ipsilateral anteroventral cochlear nucleus has on the lateral superior olive
excitatory input
Contralateral anteroventral cochlear nucleus
- excites a neuron in the medial nucleus of the trapezoid body
- sends an inhibitory signal to the lateral superior olive neuron
What happens if the aural signal is closer to the ipsilateral ear
- lateral superior olive will have a net depolarisation but will have net inhibition if the sound is closer to the other ear
How are LSO neurons stimulated
- depolarising signal from ipsilateral ear
- hyperpolarising signal from contralateral ear
- each aural signal stimulates an LSO neuron from each hemisphere
The balance between excitatory and inhibitory neurotransmission is important for…
determining the net excitation that is forwarded to the inf colliculus and the lat lemniscus
Synaptic transmission at the Calyx of Held
- 600 conventional active zones where synaptic vesicles cluster facing the POSTSYNAPTIC DENSITY
- individual active zones are similar to those found in other brain synapses
Importance of multiple sites of synaptic vesicle fusion
ensures fast, reliable synaptic transmission, such that incoming presynaptic APs reliably tirgger evoked APs even at high input frequencies
