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Resting Potential

February 23, 2015

Lab 3(MRO) and Sim 4: Equilibrium Potentials due Today Save the date: Midterm paper due Thursday, March 26

http://courses.cit.cornell.edu/bionb4910/index.html

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Information and lecture content

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Resting Potential- Concept 1: unequal distribution of ions across membrane Ion concentrations across cell membranes

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Donna Equilibrium Generation of the AP

Donna Equilibrium

Resting Potential: Battery for signal transmission

Resting Potential- Concept 2: selective membrane permeability

Why does the line deviate from the K theoretical values at lower [K]?

Execution cocktail

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At Nernst Potential Nernst Potentials of other ions

Important for resting potential

When 1 ion dominates, reverts back to Nernst equation

RP a dynamic potential based on varying ion conductances

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Action Potential another single ion domination Changes in “ RP” by changing multiple ionic conductances simultaneously- STG movie

Other contributions to RP? Any type of steady state open channel too

Membrane Model at Rest Includes Na/K ATPase

Kennedy and Takeda, 1964b Wine et al 1974 Larimer and Moore 2003 Atwood, 2008

Lab 4: Ionic basis of resting potential in crayfish Muscle

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Squid giant axon- a model prep Squid giant axon- RP experiment

Squid giant axon- membrane prep

40,000 APs can fire!

Squid giant axon- experimental chamber

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Results- K+/RP relationship

“normal”

At Rest: RP in neurons is never as negative as Keq. Why? INa = IK? Ohm’s Law for INa and IK? At Rest: gK 50X > gNA

At Rest: INa = IK? V=IR

IK = gK (Vm-EK) INa = gNa (Vm-ENa)

At Rest: INa = IK? V=IR

IK = gK (Vm-EK) INa = gNa (Vm-ENa) gK (Vm-EK) = gNa (Vm-ENa)

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Why doesn’t the AP go backwards? 2 reasons- Can it go backwards?

AP refractory periods

Refractory periods: Why are the APs getting smaller and then fail?

Note changing AP threshold too

INa

IK

Measure Im

I/V plot for current flow with larger depolarizations. Note INa reversal and IK increase with greater depol