Lec 11 - From ear to thalamus

ITD

interaural time difference, the difference in time taken for a sound to reach each ear, provides spatial information, used at low frequencies

ILD

interaural level difference, the difference between the sound pressure level at each ear, provides spatial information, used at high frequencies

HRTF

head related transfer function, pinna head torso influence changes in frequency at different heights, provides vertical location cue and spectral information

We use (ITD/ILD) at low frequencies and (ITD/ILD) at high frequencies

We use ITD at low frequencies and ILD at high frequencies

Ossicles

3 bones malleus incus stapes that move with tympanic membrane and move oval window to convert air movement into cochlear fluid movement

Cochlear fluids

perilymph is low K, endolymph is high K

Basilar membrane

moves up and down with sound, base is stiff and high frequencies, apex is floppy and low frequencies

Cochlea

frequency analyzer

Hair cells (depolarize/hyperpolarize) when stereocilia deflect towards kinocilium

depolarize

Hair cells (depolarize/hyperpolarize) when stereocilia deflect away from kinocilium

hyperpolarize

Hair cell membrane potential cascade

stereocilia move towards kinocilium, K channels open, K goes inside, depolarizes hair cell, opens Ca channels, glutamate is released

Auditory nerve

made up of spiral ganglion cell axons, tonotopically organized

Spiral ganglion cells

connect hair cells to cochlear nucleus, has best frequency

Auditory never responses at low and high frequencies

low frequencies use phase locking, high frequencies don’t use phase locking but tonotopic arrangement

Auditory pathway from cochlea to cerebral cortex

cochlea - cochlear nuclei - superior olive - inferior colliculus - medial geniculate nucleus - auditory cortex

Dorsal cochlear nucleus

receives info from cochlea, analyses frequencies (HRTF), projects directly to inferior colliculus

Ventral cochlear nucleus

receives info from cochlea, relays info to both olives, preserving tonotopical and response timing information

Superior olive

first site to receive info from both ears, sound direction analysis, has best ITD and best ILD

Inferior colliculus

receives info from dorsal cochlear nucleus and superior olive, combines spatial and spectral information, more complex sounds

Medial geniculate nucleus

receives auditory information and sends to auditory cortex