Ear to thalamus

3 cues for localizing sounds

interaural time difference, interaural level difference, head related transfer function

ILD

difference between sound pressure level at each ear, more useful at higher frequencies

HRTF

pinna, head, and torso influence the sound before it reaches the inner ear, vertical location cue based on changes in frequency

Low frequency sounds —>

ITDs

High frequency sounds

ILDs

Sound causes —>

traveling wave in cochlea

Cochlea

acts as a frequency analyzer

Different parts of the basilar membrane —>

respond maximally to different frequencies

Hair cells

convert movement of basilar membrane into neural signals

Stereocillia deflect towards kinocillium —>

hair cells depolarize due to potassium influx

Depolarization in hair cells —>

opening of voltage gated calcium channels, calcium influx, and transmitter release

Stereocillia deflect away from kinocillium

hair cells hyperpolarize

Auditory nerve

tonotopically arranged, carries information to cochlear nucleus

Superior olive

first site recieving information from both ears

Different neurons responds best to —>

different ITDs or ILDs

ITD

difference in time taken for a sound to reach each ear

Sound causes travelling wave —>

resulting from pressure difference between fluid filled compartments

Basilar membrane

moves at frequency of stimulation, size of wave varies due to membrane stiffness

Membrane maximal movement

base for high frequenices, apex for low frequencies

Auditory pathway to cerebral cortex

spiral ganglion, auditory nerve, ventral cochlear nucleus, superior olive, inferior cochleus, MGN, auditory cortex

Auditory nerve responses at low frequencies

neurons fire action potential at particular phase of sound wave, phase locking, provides frequency information

Auditory nerve responses at high frequencies

phase locking does not occur, frequency information must be derived from tontopic arrangement of nerve fibers