Central Auditory System and Sound Localization

Question 1

What is the pathway of the central auditory system

Answer 1

hair cells –> CNVIII –> ipsilateral cochlear nucleus –> superior olivary complex (becomes bilateral input) –> inferior colliculus –> medial geniculate nucleus –> primary auditory cortex

Question 2

How are low frequency sounds localized

Answer 2

interaural time differences

Question 3

how are high frequency sounds localized

Answer 3

interaural intensity differences

Question 4

Why does a difference exist between low and high frequency sound localization

Answer 4

low frequency = sound wave is longer than the diameter of your head

high frequency = sound wave is shorter than the diameter of your head

Question 5

How does the medial super olivary complex detect timing differences

Answer 5

Sound reaches the closer ear (Ear 1) followed by the farther ear (Ear 2)

Cells in MSOC need excitation from two inputs to reach threshold (“coincidence detectors”)
Axons coming from cochlear nucleus have several collaterals leading to different MSOC nuclei (whichever MSOC soma receives “coincident” input will fire

Question 6

How does the Lateral superior olivary complex detect intensity differences

Answer 6

stronger stimulus to left ear excites left LSOC

Left ear stimulus also inhibits right lSCO via MNTB interneuron (casts a shadow on right ear)

excitation from left ear is greater then inhibition from right ear, resulting in overall excitation to brain on left side

inhibition from left ear is greater than excitation from right ear, resulting in overall inhibition on right side and no signal to brain