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Unformatted text preview: Auditory System- Mechanoreceptive system: beside vestibular system is cochlea- Has hair cells responding to sound envmt ( P air ) Middle ear mechanics- Tympanum (like drum) vibrates w/ seqce of sound pressure pulses (in air)- Lever system of ossicles in middle ear ampliFes pressure pulses on tympanum 22-fold- AmpliFed pressure exerted on oval window (membrane) of cochlea (Flled with uid)- Tube linking middle ear w/ pharynx = eustachian (or pharyngotympanic) tube- Keeps net pressure across tympanum approx equal - As P in tympanum becomes less sensitive unless it breaks- ood poisoning: microbes can creep up tube & infect cochlea/vestibular canals Diagram: Schematic of cochlear unfolded & cut thru- Made up of 2 chambers : upper chamber (Flled w/ uid), lower chamber - Separated by middle compartment- Contains basillar membrane : hair cells here, bathed in endolymph- Endolymph ionic content must be carefully regulated- Middle compartment: organ of Corti (sensory organ) - Surrounded by external space Flled w/ perilymph (not as strictly regulated, more like blood plasma)- Upper & lower chambers connected at apex of cochlea (continuous)- Pressure pulse directed across basillar membrane -> exits thru round window - Basillar membrane has natural resonances along membrane- Close to oval window, membrane is stiff & narrow- Resonance (high pitch) -> greatest amplitude vibrations here Hearing [35 mm] PSL302Y: Lecture 22, by Prof. MacKay ri., Nov. 5, 2010 1 of 7- At other end by apex, membrane is elastic & broad - Resonance (low pitch)- Natural freqcy as you get closer to apex- Matches cochleas ability to hear sound freqcies: where maximal displacement caused- High freqcy sounds cannot penetrate thru Fuid up to apex -> dont affect most cochlea- Only low pitch sounds reach apex Traveling wave (5kHz) vs. 200 Hz tone vs.- High-freqcy sound (5,000 Hz): along basillar membrane- Low-freqcy sound (200 Hz): closer to apex- or every pitch/tone, theres a point along basillar membrane where maximal displacement occurs = maximal stimulation of hair cells in cochlea Diagram: Cross-section of cochlea- Upper + lower chambers lled w/ perilymph (connected at apex)- Organ of corti: atop of basillar membrane- On top of basillar membrane: set of hair cells w/ stereocilia- Stereocilia on top stick into tectorial membrane- xn: Basillar membrane vibrates- Tectorial membrane vibrates = stereocilia bent back and forth- Waves of depol/hyperpolarization in sync w/ vibrating basillar membrane Diagram: Cross-sec of cochlear, close-up- 2 types of hair cells: outer (more common) & inner- Separated by rods of Corti (skeleton)- Reticular lamina sits on top of hair cells, stereocilia penetrate -> tectorial membrane- Inner hair cells: sensory- Generate receptor potentials- Release vesicles- Producing EPSPs in afferent axons- Outer hair cells: innervated by brainstem efferents- Inhibition : hyperpolarize (desensitize) hair cell- Very specic fxn: adjust organ of Corti...
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- Fall '11