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BIOL 4370 (20)

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York University
BIOL 4370

th Oct. 24 • Dr faure - • Sound is acoustic wave (vibration of molecules in air at a certain frequency) - acoustic wave is longitudinal (air is compressed then uncompressed) - same shape in space as in time - wave moves at velocity: wavelength is distane between peaks, period is time taken for one up-down cycle - period= wavelength/speed - number of cycles/second is frequency of 1/period - speed= frequency x wavelength • We are quite good at sound localization, especially in left right plane - we compare cues in two ears ie. Loudness, timing • External ear, middle ear and inner ear - tympanic membrane vibrates and causes stapes hits (pushes in nad out) on round window on cochlea - station 2 connects throat to middle ear - eusatchain tube keeps pressure same in inner and out ear - tenson tympani muscle and stapedius muscle contract and prevent ability of ossicles to vibrate - reflex loop • Ossicles are there because the force must be amplified (more pressure) and that 3 ossicles act as lever system (trade of distance for force) • Cochlea is 32mm long if uncoiled - fluid inside vibrates part of basilar membrane (widens as you get further from oval window 150 (20KHz) microns at base to 500 microns at apex (20Hz)) - different resonant frequency at one place (result of widening) - vibration vibrates part of basilar membrane that has equal frequency to that of sound (low at wide part and high at narrow part) • Cell bodies of axons are spinal ganglion - scala media has independent fluid (fluid is called endolymph and has high postasium levels) and has organ of cotri that has receptor hair cells that respond to cell - inbetween tectorial membrane and basilar membrane are hair cells • Acoustic transduction: • Outer hair cells: change in shape. When inner hair ce
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