Subject: Re: Basilar-membrane oscillations. From: David John SMith <smithd@xxxxxxxx> Date: Wed, 31 Mar 2010 20:19:45 -0400 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>----------MB_8CC9F482AEEE08C_5E0_E41C_web-mmc-m06.sysops.aol.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="us-ascii" Reinhart, The wine glass and tuning fork change tuning when partially submerged in= water because of an impedance change. The vibration travels through the glass or metal causing side to side disp= lacement. When the wave hits the water, it gets harder to displace the sides and som= e energy is reflected back, causing the effective shortening of the oscillating object.? It's like wav= es hitting the side of a plastic kiddie pool, some energy moves the side of the pool, some causes a smaller wave to boun= ce back. In the ear, the membrane not partially submerged, but completely submerged= in fluid.? In this case, there would=20 be no impedance change at a submergence boundary.? The impedance for force= s (internal or external) acting to displace the membrane would be the same= throughout the length of the membrane, provided the other localized fluid= boundaries (the walls of the cochlea) are constant.? The fluid will act= as a coupling device (to the walls of the cochlea...). If the viscosity= of the fluid was high (which it apparently isn't) it would also act as a= damping element.? Neither of these would change the speed of sound throug= h the membrane or the oscillating frequency or speed of the "traveling wav= e" (if there is one, which there probably isn't, as such).?=20 My theory is that the membrane would not move at all without the forces ac= ting on it through the cochlear fluid. The=20 fluid is pushing the membrane and displacing it slightly. What looks like= a wave in the membrane is a reflection of forces=20 caused by eddy currents in the fluid.? It may be that these displacements= affect the hair cells enhancing or reducing sensitivity=20 as the angle of the membrane to the eddy currents changes.? Given the amou= nt of energy it would take to displace the membrane, as it is surrounded= by fluid, it seems unlikely that the nervous system is pumping enough ene= rgy in (through=20 what phospherous channels?) to do it. I notice that the stapes is attached at the base in two places and that th= e lengths of the "legs" are not the same. This would seem to create a rocking motion rather than a direct push on th= e oval window, and cause sideways (more or less parallel to the window) currents in the fluid in ad= dition to any lengthwise displacement. I would guess we have turbulent flow in the cochlear fluid being sensed,= probably damped, and possibly enhanced by the membrane and hair cells. Still no one has answered my question on the stiffness of the cochlear wal= ls?=20 best, Dave (No phd, sorry.) =20 -----Original Message----- From: reinifrosch@xxxxxxxx <reinifrosch@xxxxxxxx> To: AUDITORY@xxxxxxxx Sent: Wed, Mar 31, 2010 9:57 am Subject: [AUDITORY] Basilar-membrane oscillations. =20 =20 =20 Dear colleagues,=20 =20 Sorry, one more posting on the stiffness of the basilar membrane.=20 =20 In my message of March 27, I =20 mentioned the guinea-pig BM oscillation frequency of 2.3 kHz measured by= Mammano =20 and Ashmore (1993), "Reverse =20 transduction measured in the isolated cochlea by laser Michelson =20 interferometry", Nature 365, 838-841. How much higher =20 =20 would the frequency be if the liquid above and below the partition were re= moved?=20 =20 One of my wine glasses when empty =20 oscillates at ~523 Hz. If it is filled with water, the frequency drops to= ~311 =20 Hz, i.e., by a major sixth. If the glass =20 is completely under water, the frequency is ~208 Hz, lower than when empty= by as =20 much as a major tenth.=20 =20 A tuning fork, =20 however, sinks from 440 Hz to ~415 Hz when immersed, i.e., by a semitone= only.=20 =20 I believe that in these cases, and also =20 in the mentioned guinea pig experiment, evanescent liquid-pressure waves= occur. =20 In those, the liquid particles move =20 back and forth (whereas in travelling surface waves they move on elliptica= l =20 trajectories). The drop in oscillation =20 frequency of resonators by immersing is severe if the streamlines of the= =20 evanescent waves are long. In the mentioned =20 guinea-pig experiment, at the beginning of the rectangular electric-curren= t =20 pulse, the BM was raised at the pipette =20 location (pipette diameter 5 micro-m), and probably was lowered at places= more =20 basal and apical by 30 micro-m or so. =20 The typical streamline length (approximately half-circular, from raised-BM= place =20 to lowered-BM place) may have been ~50 =20 micro-m. The liquid on both sides of the partition thus may have increased= the =20 effective BM surface mass density from =20 ~0.1 kg / m^2 to ~0.2 kg / m^2, and so decreased the BM resonance frequenc= y by a =20 factor of ~sqrt(0.5) =3D 0.7, i.e. by =20 (very roughly) about half an octave. =20 =20 An extrapolation of the exponential guinea-pig BM-resonator map that I =20 presented in Fig. 3 of "Old and New Cochlear Maps", Canadian Acoustics Vo= l. 37, =20 No. 3 (2009) 174-175, up to x =3D 11 mm =20 from base, yields a frequency of 3.7 kHz, greater than the mentioned =20 experimental result of 2.3 kHz by about a minor =20 sixth.=20 =20 Reinhart. =20 =20 Reinhart Frosch,=20 Dr. phil. nat.,=20 r. PSI and ETH Zurich,=20 Sommerhaldenstr. 5B,=20 CH-5200 Brugg.=20 Phone: =20 =20 0041 56 441 77 72.=20 Mobile: 0041 79 754 30 32.=20 E-mail: reinifrosch@xxxxxxxx .=20 =20 =20 ----------MB_8CC9F482AEEE08C_5E0_E41C_web-mmc-m06.sysops.aol.com Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="us-ascii" <div style=3D"font-family: arial; color: black; font-size: 10pt;"> Reinhar= t,<br> <br> The wine glass and tuning fork change tuning when partially submerged in= water because of an impedance change.<br> The vibration travels through the glass or metal causing side to side disp= lacement.<br> When the wave hits the water, it gets harder to displace the sides and som= e energy is reflected back,<br> causing the effective shortening of the oscillating object. It's lik= e waves hitting the side of a plastic kiddie pool,<br> some energy moves the side of the pool, some causes a smaller wave to boun= ce back.<br> <br> In the ear, the membrane not partially submerged, but completely submerged= in fluid. In this case, there would <br> be no impedance change at a submergence boundary. The impedance for= forces (internal or external) acting to displace the membrane would be th= e same throughout the length of the membrane, provided the other localized= fluid boundaries (the walls of the cochlea) are constant. The fluid= will act as a coupling device (to the walls of the cochlea...). If the vi= scosity of the fluid was high (which it apparently isn't) it would also ac= t as a damping element. Neither of these would change the speed of= sound through the membrane or the oscillating frequency or speed of the= "traveling wave" (if there is one, which there<br> probably isn't, as such). <br> <br> My theory is that the membrane would not move at all without the forces ac= ting on it through the cochlear fluid. The <br> fluid is pushing the membrane and displacing it slightly. What looks like= a wave in the membrane is a reflection of forces <br> caused by eddy currents in the fluid. It may be that these displacem= ents affect the hair cells enhancing or reducing sensitivity <br> as the angle of the membrane to the eddy currents changes. Given the= amount of energy it would take to displace the membrane, as it is surroun= ded by fluid, it seems unlikely that the nervous system is pumping enough= energy in (through <br> what phospherous channels?) to do it.<br> <br> <br> I notice that the stapes is attached at the base in two places and that th= e lengths of the "legs" are not the same.<br> This would seem to create a rocking motion rather than a direct push on th= e oval window, and cause<br> sideways (more or less parallel to the window) currents in the fluid in ad= dition to any lengthwise displacement.<br> I would guess we have turbulent flow in the cochlear fluid being sensed,= probably damped, and possibly enhanced<br> by the membrane and hair cells.<br> <br> <br> Still no one has answered my question on the stiffness of the cochlear wal= ls? <br> <br> <br> <br> best,<br> Dave<br> (No phd, sorry.)<br> <br> <br> </div> <div> <br> </div> <div><br> </div> -----Original Message-----<br> From: reinifrosch@xxxxxxxx <reinifrosch@xxxxxxxx><br> To: AUDITORY@xxxxxxxx<br> Sent: Wed, Mar 31, 2010 9:57 am<br> Subject: [AUDITORY] Basilar-membrane oscillations.<br> <br> <br> <div id=3D"AOLMsgPart_0_d180d887-35be-43fc-bde8-b755dd2006b4" style=3D"mar= gin: 0px; font-family: Tahoma,Verdana,Arial,Sans-Serif; font-size: 12px;= color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);"> <br> <br> <pre style=3D"font-size: 9pt;"><tt>Dear colleagues, <br> <br> Sorry, one more posting on the stiffness of the basilar membrane. <br> <br> In my message of March 27, I <br> mentioned the guinea-pig BM oscillation frequency of 2.3 kHz measured by= Mammano <br> and Ashmore (1993), "Reverse <br> transduction measured in the isolated cochlea by laser Michelson <br> interferometry", Nature 365, 838-841. How much higher <br> <br> would the frequency be if the liquid above and below the partition were re= moved? <br> <br> One of my wine glasses when empty <br> oscillates at ~523 Hz. If it is filled with water, the frequency drops to= ~311 <br> Hz, i.e., by a major sixth. If the glass <br> is completely under water, the frequency is ~208 Hz, lower than when empty= by as <br> much as a major tenth. <br> <br> A tuning fork, <br> however, sinks from 440 Hz to ~415 Hz when immersed, i.e., by a semitone= only. <br> <br> I believe that in these cases, and also <br> in the mentioned guinea pig experiment, evanescent liquid-pressure waves= occur. <br> In those, the liquid particles move <br> back and forth (whereas in travelling surface waves they move on elliptica= l <br> trajectories). The drop in oscillation <br> frequency of resonators by immersing is severe if the streamlines of the= <br> evanescent waves are long. In the mentioned <br> guinea-pig experiment, at the beginning of the rectangular electric-curren= t <br> pulse, the BM was raised at the pipette <br> location (pipette diameter 5 micro-m), and probably was lowered at places= more <br> basal and apical by 30 micro-m or so. <br> The typical streamline length (approximately half-circular, from raised-BM= place <br> to lowered-BM place) may have been ~50 <br> micro-m. The liquid on both sides of the partition thus may have increased= the <br> effective BM surface mass density from <br> ~0.1 kg / m^2 to ~0.2 kg / m^2, and so decreased the BM resonance frequenc= y by a <br> factor of ~sqrt(0.5) =3D 0.7, i.e. by <br> (very roughly) about half an octave. <br> <br> An extrapolation of the exponential guinea-pig BM-resonator map that I <b= r> presented in Fig. 3 of "Old and New Cochlear Maps", Canadian Acoustics Vo= l. 37, <br> No. 3 (2009) 174-175, up to x =3D 11 mm <br> from base, yields a frequency of 3.7 kHz, greater than the mentioned <br> experimental result of 2.3 kHz by about a minor <br> sixth. <br> <br> Reinhart. <br> <br> Reinhart Frosch, <br> Dr. phil. nat., <br> r. PSI and ETH Zurich, <br> Sommerhaldenstr. 5B, <br> CH-5200 Brugg. <br> Phone: <br> <br> 0041 56 441 77 72. <br> Mobile: 0041 79 754 30 32. <br> E-mail: <a href=3D"mailto:reinifrosch@xxxxxxxx">reinifrosch@xxxxxxxx</= a> . <br> </tt></pre> <br> </div> <br> =3D ----------MB_8CC9F482AEEE08C_5E0_E41C_web-mmc-m06.sysops.aol.com--