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Transcript of Audition
auditory receptor cells = hair cells
"cilium" - Latin for eyelash
cilia of hair cells bent between basilar & tectorial membranes Cochlea "scala" = chamber
the 3 chambers within the cochlea are filled with what?
the oscillation of the ossicles causes the ______ to vibrate from the base of top chamber to apex, then around to round window at base of bottom chamber Audition Anatomy of Auditory System Transduction note: K+ is the ion involved in this process, not Na+
when cilia are bent, K+ gates open, and K+ enters cell; the polarity is decreased
Ca++ enters cell, release glutamate (excitatory NT)
when cilia are bent the opposite way, K+ leaves cell and Ca++ is pumped out, restoring polarity
hair cells show _______ potentials, while auditory nerve fibers show _______ potentials. Temporal Coding sound affects the RATE at which the basilar membrane vibrates
e.g. 500 Hz = membrane moves up & down 500 times per second
another way to code for a sound's frequency is to measure the RATE of action potentials
we can discriminate up to about 4000 Hz, but action potentials of spiral ganglions are limited to 1000 times/second
how do we get past this? Localization Intensity differences: the ear that is closer to the source will be more intense because of our HEAD SHADOW; better for HIGH frequencies why is the oval window 17x smaller than the tympanic membrane? scala vestibuli scala tympani scala media Place Coding each PLACE resonates with certain frequencies
any given frequency will have a place of maximum displacement and thus maximum NT release
note: places surrounding will still be displaced, but to a lesser degree
ACROSS FIBER CODING Fourier Analysis phase locked: can only fire at the same phase; the ganglions work together to make sure every peak is covered Phase differences: detect difference in peak (more condensed molecules) vs. trough (more spread out molecules) Timing differences: interaural time-disparity detectors; "onset" cells race to superior olive
note: this is for left/right distinction, must use another localization method for sounds that are equi-distant from 2 ears