localization of sound

types of localization

1. MSO

2. LSO

3. encoded amplitude

MSO

low frequency; less than 3000Hz

part in brain that helps figure out where sounds are coming from

cochlear nucleus

part where sound info gets sent to first; one for left and right auditory system

coincident detector

cells in MSO needs 2 signals one from left and right auditory system to be activated at the same time

MSO cell organization

have left and right ear leading neurons; cells are closer to left ear nucleus or right ear nucleus

the distance between cells helps figure out where sound is coming from (sounds on right reach left leading neuron first and vice versa for sounds on left)

axonal connections

pathways that carry sound messages; length of these pathways help decide which MSO cell gets the sound message at the right time (ie. if you leave earlier you’ll get farther than other person, if you both leave at same time you’ll arrive at same place at same time)

MSO process

1. MSO cells receives coincident detector from right and left cochlear nucleus

2. length of axonal connections determine which MSO cell receives coincided activation by action potential

LSO

high frequency sound; greater than 3000Hz

LSO process

1. cochlear nucleus projects directly to ipsilateral LSO which increases sound on ipsilateral side

2. whilst projecting to LSO, cochlear nucleus projects to contralateral MNTB which inhibits contralateral LSO

LSO example

right LSO will have louder sound because left LSO is being inhibited by the activation of left MNTB

MNTB

inhibits ipsilateral LSO

how is amplitude encoded

1. proportion of activated hair cells

2. firing rate of individual hair cells

proportion of activated hair cells

the more hair cells activated at once, the louder the sound / amplitude

firing rate of individual hair cells

faster the hair cells send signals to brain, the louder the sound/amplitude