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Unformatted text preview: l − ]S + Ⱥlog I0 +
+ log[Cl − ]G Ⱥ ln10 ⋅ kT q
Ⱥ Ⱥ Ⱥ
−0.5 Ⱥ = − log[Cl − ]S + Ⱥ−6 +
− 3Ⱥ Ⱥ 60 m Ⱥ € = − log[Cl − ]S 17.3 c. Next assume the membrane is permeable only to Ca2+ and the trapped Ca2+ concentration between the membrane and the gate of the ISFET is 1 mmol/L. As before derive and sketch, on logarithmic axes, the drain current as a function of Ca2+ concentration. For Ca2+, z = +2: Ⱥ
Ⱥ 1
−VTH
1
log( I DS ) = ⋅ log[ A z ]S + Ⱥlog I0 +
− ⋅ log[ A z ]G Ⱥ z
ln10 ⋅ kT q z
Ⱥ Ⱥ Ⱥ
Ⱥ −VTH
= 0.5 ⋅ log[Ca 2+ ]S + Ⱥlog I0 +
− 0.5 ⋅ log[Ca 2+ ]G Ⱥ ln10 ⋅ kT q
Ⱥ Ⱥ Ⱥ
Ⱥ −0.5
= 0.5 ⋅ log[Ca 2+ ]S + Ⱥ−6 +
+ 1.5Ⱥ Ⱥ Ⱥ 60 m € = 0.5 ⋅ log[Ca 2+ ]S − 12.8 Slopes are 1,
1 and 0.5 respectively. Problem 3: Short response (no more than one paragraph each). a. What is a rheobase current and where is it used? The Strength
Duration Curve for a typical neural membrane flattens out with long stimulus durations, reaching an asymptote called the RHEOBASE. When the stimulus strength is below the rheobase, stimulation is ineffective even when stimulus duration is very long. The rheobase tells the minimum strength of stimulation for effective stimulation. Source: http://en.wikipedia.org/wiki/File:Rheobase_chronaxie.png http://www.medicine.mcgill.ca/physio/vlab/cap/S
D.htm b. What is the difference between macroshock and microshock? Macroshock: Current is applied externally and flows throughout the body. A small fraction of total current flows through the heart. Safety limit: 10
20 mA Microshock: Invasive devices apply current. All current...
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This document was uploaded on 02/19/2014 for the course BENG 186B at UCSD.
 Winter '08
 PeterChen

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