Chap4. The auditory nerve Pronounced by Hwang semi

-stage of auditory system -Understand some of changes in auditory nerve activity -relate to the psychophysical capabilities Overview of books (6-8 central auditory, 9 psychophysical of auditory, 10 Sensorineural hearing loss) introduction

physiology How to catch the fibres? In animal, 418 fibres -> not sufficient, can easily be lost in recording Tasaki(1954) use drill through temporal bone (just takes 10s ) Nowadays open occipital bone-> insert retractor(with microelectrode) around edge of cerebellum->brainstem eliminate until auditory meatus and cochlear nucleus, spiral gainglion directly become visible. (takes many 10 of minutes)

Nearest basilar membrane ueuron (dendrite-information, cellbody, axon)-> Spliral gainglion

Anatomy Auditory nerve fibres -cat: fibres, man: OHC -> spiral ganglion cell (5~10%), include 6 fibres, branch to 10 hair cells OHC~IHC =0.6mm IHC -> majority direct connet ->entry into the cochlear(include 20 fibres- branch to 1 hair cell -> because of cellbody shape and myelinated)

IHC ( 59% in case of cat, bipolar cell bodies, myelinated cell body, TYPE 1 cell, auditory nerve response i.e. driven tones, show spontaneous activity) OHC(monopolar, not myelinated, etc. deal with chap5)

Other specificities (absolute refractory period, all or none)

Microelectrode tip size : < 0.3 μm ¼ discharge < 20s Most discharge < 0.5s * Other group max 120/s, avg 60~80 discharge/.s Random spontaneous activity

Degree of freq. selectivity and depth vary from species to species. OHC thresholds are low level IHC thresholds are high level High thresholds-> broadly tuned tail 70% fibres below 10dB 80% fibres below 20dB and low spontaneous

Response to tones – freq. selectivity Fibres response to single tone, excitatory (not inhibitory), possible to express PSTH(post stimulus time histogram) consisted of column, bin. Tone-burst have sharp onset, within 10~20ms drop sharply. (next page)

PSTH in toneburst In Common, 5 ~30 spikes/s, CF (characteristic freq, or best -): low threshold at one freq.

PST-histogram vs. interval historgram 1/T (Hz) 1000/ / / / / /

Degree of freq. selectivity

Typical tuning curves across freq. Two frbres in same animal, under such circumstances.

CF vs. Q10 in cat Values measured for BM and HC response.

Freq. selectivity 1) slope of tuning curve above (below CF) 2)Q10 Many species in 10KHz the steepest slope (high freq. 100~600dB/Octave->steep sometimes 1000dB/Octave, low freq. slope 80~250dB/octave->tail

CF & Q10 Spontaneous rate = 15/sec CF? Q10 value? 17500/ ( ) = 17.5

Dynamic range at one freq. is limited 20~50dB. Firing rate depends on the stimulus freq. Fire rated by combination of intensities and freq -> iso-response or iso-reate contours

Iso curve show that as intensity raise freq. evoking the highest firing rate Iso-displacement curves for the basilar membrane

Iso -curve Low intensity the greatest response is in near the CF Most effective freq. moves toward 1KHz

Firing saturate (about 70dB)

Add to picture Stiffness application -> high or low freq.

Phase locking Related to different aspect of IHC function( based on in crease in firing rate and sensitive a low freq. tone.

Response to clicks(PSTH) Click: last short time, spread energy wide freq. range Low freq several decay due to oscillation.

Histogram correspond half cycle of decaying oscillation on the basilar membrane( upward motion, responsible for excitation rarefaction click produces earliest response(A), condensation (B), compound(C) -> possible to suppress

Thanks for listening Continue to be pronounced by Kim Hye-mi